JP2000337198A - Combustion control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the combustion control device of an internal combustion engine which can restrain the discharge of NOx from NOx catalyst, at the enforcement time of a rich spike treatment. SOLUTION: An electronic control device (ECU) 60 can switch a combustion mode from a stratified charge combustion to a homogeneous rich combustion at the enforcement time of a rich spike treatment. Meantime, at first when the combustion mode is a stratified charge combustion, ECU 60 can set and change the target opening TRT of a throttle valve 34 and the target opening EGR of an EGR valve 43 to the opening requested at the homogeneous rich combustion time and also increase the final fuel injection amount QINJ to the injection amount following to the throttle opening TRT. Next, after elapsing a prescribed time, the set of the target throttle opening TRT and target exhaust gas recirculation valve opening EGR is not changed and only the final fuel injection amount QINJ is increased and the combustion mode is switched from the stratified charge combustion to the homogeneous rich combustion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion control device for an internal combustion engine that executes a rich spike process for temporarily switching the combustion mode from stratified combustion to homogeneous rich combustion.

[0002]

2. Description of the Related Art Conventionally, in addition to homogeneous combustion in which fuel is injected during an intake stroke and uniformly dispersed and burned in an engine combustion chamber, the fuel is injected during a compression stroke and unevenly distributed near a spark plug in the engine combustion chamber. There has been proposed an internal combustion engine that performs stratified combustion in which the fuel is burned.
No. 32071).

In such an internal combustion engine, since nitrogen oxides (NOx) contained in exhaust gas increase during stratified charge combustion, a NOx storage reduction catalyst (hereinafter referred to as "NOx catalyst") is provided in an exhaust passage.
(Abbreviated as). This NOx catalyst stores NOx in exhaust when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio as in the case of stratified charge combustion, while the air-fuel ratio is set richer than the stoichiometric air-fuel ratio. During the operation, the stored NOx is reduced to nitrogen (N2) and released into the exhaust passage, thereby purifying the NOx.

In the internal combustion engine equipped with such a NOx catalyst, when the stratified charge combustion is continued for a long time and the amount of NOx occluded reaches near its limit, the combustion mode is changed from the stratified charge combustion to the homogeneous rich combustion. A process of temporarily switching, that is, a so-called rich spike process is executed. By executing this rich spike processing, NOx stored in the NOx catalyst is released into the exhaust passage after being purified, so that the NOx storage capacity of the catalyst is maintained.

Further, when the combustion mode is switched from stratified combustion to homogeneous rich combustion during rich spike processing, simply increasing the amount of fuel injection causes an unnecessary increase in engine output (torque) accompanying the switching of the combustion mode. Becomes
Thus, conventionally, as described in the above-mentioned publication, when switching the combustion mode, the intake air amount is reduced by simultaneously reducing the throttle opening.
As a result, the combustion mode can be switched while maintaining the engine torque constant.

[0006]

By the way, when the air-fuel ratio of the NOx catalyst is maintained near the stoichiometric air-fuel ratio (hereinafter referred to as "stoichiometric vicinity") in a state where the NOx storage amount has increased to near its limit amount, NOx Has the property of being released without purification. For this reason, the following problems cannot be ignored when performing the rich spike processing.

That is, while the fuel injection amount changes rapidly with the change in the valve opening time of the fuel injection valve, the intake air amount changes unless the predetermined response delay time elapses. Does not change to the amount corresponding to. Therefore, as shown in the timing chart of FIG. 7, when the rich spike processing is started (timing t0 shown in FIG. 7), the fuel injection amount rapidly increases with an increase in the valve opening time of the fuel injection valve. However, the intake air amount gradually decreases to an amount corresponding to the time of the homogeneous rich combustion later than the increase of the fuel injection amount.

Since the air-fuel ratio also gradually changes from the lean region to the rich region due to the response delay of the intake air amount, the air-fuel ratio is relatively long to pass near the stoichiometric region. It takes time (τs). As a result, the amount of NOx that is released from the NOx catalyst without being purified increases.
A substantial reduction in the purification capacity of the catalyst is inevitable.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a combustion control device for an internal combustion engine that can suppress the release of NOx from a NOx catalyst when performing rich spike processing. It is in.

[0010]

The means for achieving the above object and the effects thereof will be described below. In order to achieve the above object, in the invention described in claim 1,
Combustion control of an internal combustion engine that performs stratified combustion as a form of directly injecting fuel into a cylinder during a compression stroke and performs homogeneous rich combustion as a form of injecting fuel during an intake stroke during the compression stroke In the device, when switching from stratified combustion to homogeneous rich combustion so that the engine torque becomes constant, the throttle opening is set to the opening required for homogeneous rich combustion without changing the fuel injection mode, and the fuel injection amount is set. The gist of the present invention is to provide a switching means for changing the fuel injection mode and switching the combustion mode to the homogeneous rich combustion after once executing the combustion mode controlled according to the set throttle opening.

[0011] In the configuration, when the rich spike processing is executed, when switching from the stratified combustion to the homogeneous rich combustion, first, only the setting of the throttle opening is set during the stratified combustion without changing the fuel injection mode. The setting is changed from the set opening to the opening required for homogeneous rich combustion, and the combustion mode for controlling the fuel injection amount according to the set throttle opening is once executed. Thereafter, the fuel injection mode is changed to switch the combustion mode to homogeneous rich combustion. Therefore, when performing the rich spike processing, it is possible to reduce the time required for the NOx to pass through the air-fuel ratio region near stoichiometry where the NOx is released without being purified by the NOx catalyst, while eliminating the change in the engine torque. As a result, deterioration of NOx emission can be suppressed.

According to a second aspect of the present invention, in the combustion control apparatus for an internal combustion engine according to the first aspect, the switching means changes the throttle opening during homogeneous rich combustion without changing the fuel injection mode. The execution period of the combustion mode in which the required opening is set and the fuel injection amount is controlled in accordance with the set throttle opening is set to be shorter than the response delay period of the change in the intake air amount of the engine accompanying the setting of the throttle opening. The gist is to set a long period.

When the combustion mode is switched from stratified combustion to homogeneous rich combustion, the air-fuel ratio shifts from a lean region to a rich region. At that time, the air-fuel ratio changes according to the change in the intake air amount of the engine.
The transition of the air-fuel ratio is performed after the end of the change in the intake air amount, that is, without being affected by the response delay of the change in the intake air amount. Therefore, it is possible to more reliably reduce the time required for the air-fuel ratio to pass near the stoichiometric ratio. As a result, the deterioration of NOx emission can be surely suppressed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment in which the present invention is applied to a combustion control device for a direct fuel injection type gasoline engine will be described below with reference to FIGS.

FIG. 1 is a schematic configuration diagram showing a combustion control device according to the present embodiment. Engine 10 shown in FIG.
Cylinders 1 formed in the cylinder block 11
In FIG. 5 (one of which is shown in FIG. 1), a piston 13 connected to a crankshaft 14 via a connecting rod 16 is provided so as to be able to reciprocate.
A combustion chamber 17 is defined by the upper surface of the piston 13, the inner wall surface of the cylinder 15, and the lower surface of the cylinder head 12. The combustion chamber 17 is connected to an intake pipe 20 and an exhaust pipe 21 via an intake port 18 and an exhaust port 19 formed in the cylinder head 12.

A surge tank 22 is provided in the intake pipe 20. A throttle valve 34 whose opening (throttle opening) is adjusted by a throttle motor 54 is provided upstream of the surge tank 22. This throttle valve 3
4 regulates the amount of intake air introduced into the combustion chamber 17.

The cylinder head 12 is provided with an injector 50 for directly injecting fuel into the combustion chamber 17 and a spark plug 26 for igniting an air-fuel mixture in the combustion chamber 17 for each cylinder 15. The fuel injection amount and the fuel injection timing are adjusted based on the opening / closing operation of the injector 50.

The exhaust pipe 21 is provided with a three-way catalyst 23,
Further downstream, a NOx catalyst 24 is provided. Exhaust gas discharged from the combustion chamber 17 to the exhaust pipe 21 is purified by these catalysts 23 and 24.

In the intake pipe 20, a throttle valve 34
An accelerator sensor 64 is provided in the vicinity of. The accelerator sensor 64 is connected to an accelerator pedal 46 operated by a driver via a wire (not shown), and outputs a detection signal corresponding to the depression amount of the accelerator pedal 46 (accelerator opening ACCP). Is done.

The exhaust pipe 21 is provided with an exhaust gas recirculation (EGR).
It is connected to the surge tank 22 via the passage 42.
In the middle of the EGR passage 42, an exhaust gas recirculation valve (EG
R valve 43 is provided. This EGR valve 4
3, the amount of exhaust gas (EGR amount) recirculated from the exhaust pipe 21 to the intake pipe 20 through the EGR passage 42.
Is adjusted.

A crank sensor 65 is provided near the crankshaft 14.
Cam shafts 30, 31 which rotate in synchronization with the rotation of
A cam sensor 66 is provided in the vicinity of one side. From these sensors 65 and 66, the rotation angle (crank angle CA) of the crankshaft 14 and the crankshaft 14
A signal corresponding to the rotation speed (engine rotation speed NE) is output.

The surge tank 22 is provided with an intake pressure sensor 67, which outputs a detection signal corresponding to the pressure of the intake air in the intake pipe 20 (intake pressure PM).

The detection signals of these various sensors 64 to 67 are input to an electronic control unit (hereinafter abbreviated as “ECU”) 60 of the engine 10. The ECU 60 detects the accelerator opening ACCP, the crank angle CA, the engine speed NE, and the intake pressure PM based on these detection signals. EC
U60 drives the solenoid valve of the injector 50, the throttle motor 54, the EGR valve 43, and the like based on these detected values, thereby setting the fuel injection amount, the fuel injection timing, the intake air amount, the EGR amount, and the like to the engine operating state. Control to fit. The ECU 60 includes a memory 61 in which a control program and function data for executing such various controls according to predetermined procedures are stored in advance.

The engine 10 in the present embodiment can be switched between the following four modes. 1. Stratified Combustion When stratified combustion is selected as the combustion mode, the fuel injection timing is set in the latter half of the compression stroke (compression stroke injection). The average air-fuel ratio of the air-fuel mixture in the combustion chamber 17 is set leaner than the stoichiometric air-fuel ratio.

2. Homogeneous stoichiometric combustion When homogeneous stoichiometric combustion is selected as the combustion mode, the fuel injection timing is set during the intake stroke (intake stroke injection), and the air-fuel ratio is set near stoichiometric.

3. Homogeneous rich combustion When the homogeneous rich combustion is selected as the combustion mode, the fuel injection timing is set during the intake stroke (intake stroke injection), as in the homogeneous stoichiometric combustion. The air-fuel ratio is set to be richer than the stoichiometric air-fuel ratio. This homogeneous rich combustion is selected only during the rich spike processing described later.

4. Transient stratified combustion This transient stratified combustion is temporarily selected during the switching of the combustion mode from stratified combustion to homogeneous rich combustion by the rich spike processing and during the transition from homogeneous rich combustion to stratified combustion. When the transition stratified combustion is selected as the combustion mode, the fuel injection timing is set to the latter half of the compression stroke (compression stroke injection) as in the stratified combustion, and the throttle opening and E
Each of the GR openings is set to be smaller than that in the stratified combustion and equal to the opening in the homogeneous rich combustion.
Therefore, the amount of intake air is smaller than in stratified combustion,
It is equal to the amount during homogeneous rich combustion. Further, the fuel injection amount is increased from the fuel injection amount at the time of stratified combustion to an amount that can suppress a decrease in the engine torque with the decrease in the intake air amount. The average air-fuel ratio of the air-fuel mixture in the combustion chamber 17 is set leaner than the stoichiometric air-fuel ratio.

Switching between these combustion modes is performed by the ECU 60.
This is performed based on the engine operating state, the NOx storage amount of the NOx catalyst 24, and the like. Hereinafter, the procedure for switching the combustion mode will be described.

First, the ECU 60 obtains the basic fuel injection amount Qb from a map showing the relationship between the accelerator opening ACCP and the engine speed NE and the basic fuel injection amount Qbse as shown in FIG.
Ask for se. This map is stored in the memory 61. This basic fuel injection amount Qbse
This reflects the load state of the load.

Next, the ECU 60 determines the combustion mode instruction value fmode based on the basic fuel injection amount Qbse and the engine speed NE thus obtained. The combustion mode instruction value fmode is for determining which of the above-described combustion modes is to be selected.

For example, the combustion mode instruction value fmode
Is "0", stratified charge combustion is selected as the combustion mode, and when the combustion mode instruction value fmode is "12", homogeneous stoichiometric combustion is selected as the combustion mode. Further, when the combustion mode instruction value fmode is “2”, the transitional stratified combustion is selected as the combustion mode, and when the combustion mode instruction value fmode is “11”, the homogeneous rich combustion is performed as the combustion mode. Each is selected.

The memory 61 of the ECU 60 stores function data defining the relationship between the value of the combustion mode instruction value fmode, the engine speed NE, and the basic fuel injection amount Qbse. FIG. 3 is a map schematically showing the function data.

For example, when the engine speed NE and the basic fuel injection amount Qbse change from the state shown at the point A to the state shown at the point B along the dashed line shown in FIG. 3, the combustion mode instruction value fmode becomes "0". "To" 12 ", and the combustion mode is changed from stratified combustion to homogeneous stoichiometric combustion.

On the other hand, when predetermined execution conditions are satisfied, the ECU 60 starts rich spike processing. When the rich spike processing is started, the combustion mode instruction value fmo
de is switched from "0" to "11" via "2", and with this switching, the combustion mode is forcibly switched from stratified combustion to transient rich stratified combustion to homogeneous rich combustion.

Hereinafter, such a rich spike processing will be described. In the rich spike processing according to the present embodiment, when changing the fuel injection amount and the intake air amount from the amount corresponding to the stratified combustion to the amount corresponding to the homogeneous rich combustion, the intake air amount having a response delay in the change. Is changed first, and the fuel injection amount is changed again after a predetermined period has elapsed. By shifting the timing of changing the intake air amount and the fuel injection amount in this manner, the air-fuel ratio is quickly shifted from the lean region to the rich region, and the time required for the air-fuel ratio to pass near the stoichiometric ratio is reduced. I have to.

Next, an example of the execution procedure of the rich spike processing will be described in detail with reference to the flowcharts shown in FIGS. 4 and 5 and the timing chart shown in FIG.
The ECU 60 executes a series of processes shown in the flowcharts of FIGS. 4 and 5 at, for example, a predetermined crank angle cycle.

First, in step 100 shown in FIG. 4, the ECU 60 determines the current accelerator opening ACCP, the crank angle CA, and the current accelerator opening ACCP based on the detection signals output from the accelerator sensor 64, the cam sensor 66, the crank sensor 65, and the like. And data such as the engine speed NE. Then, based on the accelerator opening ACCP and the engine speed NE, the current basic fuel injection amount Q is obtained from the map.
bse is obtained, and the routine proceeds to step 110.

In step 110, the ECU 60
Determines whether the rich spike processing execution flag (hereinafter simply referred to as the RS execution flag) XRS is “ON”. This RS execution flag XRS is a flag for determining whether or not the rich spike processing is being executed.
The flag is set to “ON” during execution of the rich spike processing, and is set to “OFF” during non-execution. The RS execution flag XRS is turned “ON” at timing t1 and “OFF” at timing t4 in FIG. Therefore, in FIG. 6, the rich spike processing is performed at the timing t.
It is executed during the period from 1 to t4.

Here, the RS execution flag XRS is currently "O
N ", that is, when it is determined that the rich spike processing is currently being executed, the ECU 60 proceeds to the processing of step 210. On the other hand, when it is determined that the rich spike processing is not currently being executed, the ECU 60 proceeds to the processing of step 120. Hereinafter, a case will be described in which the rich spike process is not being executed and the process proceeds to step 120.

The ECU 60 determines in step 120
It is determined whether the value of the combustion mode instruction value fmode is “0”, that is, whether stratified combustion is currently being performed.
If the ECU 60 determines that the value of the combustion mode instruction value fmode is not “0”, the ECU 60 temporarily ends the process. This is because the ECU 60 is currently executing the combustion mode instruction value fmod.
The value of e is "12", because it is determined that the homogeneous stoichiometric combustion is being performed as the combustion mode. That is, rich spike processing is not performed during homogeneous stoichiometric combustion. The value of the combustion mode instruction value fmode is “1”.
In the case of "2", the throttle opening, fuel injection amount, and the like corresponding to homogeneous stoichiometric combustion are calculated through another processing routine.

On the other hand, if it is determined in step 120 that the value of the combustion mode instruction value fmode is “0”, the ECU 60 proceeds to step 130. In this step 130, the ECU 60 determines the relationship between the engine speed NE and the basic fuel injection amount Qbse and the target throttle opening TRT (= trt0map (NE, Qbse)) from a map for stratified combustion (not shown). The current target throttle opening TRT is obtained. Similarly, the engine speed NE, the basic fuel injection amount Qbse, and the target exhaust gas recirculation valve opening EGR (= egr0map (N
E, Qbse)), the current target exhaust gas recirculation valve opening EGR is obtained from a map for stratified combustion (not shown) showing the relationship
Ask for. The ECU 60 also calculates the final fuel injection amount QINJ
Is set to an amount equal to the current basic fuel injection amount Qbse,
Move to step 140.

In step 140, the ECU 60
Determines whether the count number of the catalyst counter CNT1 has reached a predetermined number α. Here, the catalyst counter CNT1
Is a timer counter that accumulates and counts a period in which stratified combustion is selected as the combustion mode, that is, a period in which the value of the combustion mode instruction value fmode is set to “0” or “2”. It is operated through a routine. The NO stored in the NOx catalyst 24 according to the count number of the catalyst counter CNT1.
The x amount is estimated. Here, the predetermined number α is set as a value when the amount of NOx stored in the NOx catalyst 24 has reached near the limit amount.

In step 140, the ECU 60 determines that the count number of the catalyst counter CNT1 is still a predetermined number α.
If it is determined that the number has not reached the maximum value, it is not necessary to execute the rich spike processing, and the processing is temporarily terminated. On the other hand, when determining that the count number of the catalyst counter CNT1 has reached the predetermined number α, the ECU 60 proceeds to step 150 and thereafter and starts the rich spike processing. In the timing chart shown in FIG. 6, the point in time when the count number of the catalyst counter CNT1 reaches the predetermined number α is
This is shown at timing t1.

In step 150, the ECU 60
Instructs the fmode counter CNT2 to start the addition operation, and sets the RS processing execution flag XRS to "ON". Further, the combustion mode instruction value fmode
Is "2" (FIG. 6). Here, the fmode counter CNT2 is a timer counter that counts a period during which the combustion mode is maintained in the transitional stratified combustion, and is operated through another processing routine.

In step 160, the ECU 60
Is the engine speed NE, the basic fuel injection amount Qbse and the target throttle opening TRT (= trt11map (NE, Qbse))
Map for homogenous rich combustion (not shown)
From the target throttle opening TRT. Similarly, from a map (not shown) for homogeneous rich combustion, which shows a relationship between the engine rotational speed NE and the basic fuel injection amount Qbse and the target exhaust gas recirculation valve opening EGR (= egr11map (NE, Qbse)). The recirculation valve opening EGR is obtained. Incidentally, the target throttle opening TRT (= trt0map) and the target exhaust gas recirculation valve opening EGR (= egr0map) calculated based on the map for stratified combustion and the map for homogeneous rich combustion are calculated. Target throttle opening TRT (= trt11map) and target exhaust gas recirculation valve opening EG
When compared with R (= egr11map), TRT (= egr11map) is always
trt0map)> TRT (= trt11map), EGR (= egr0ma)
p)> EGR (= egr11map).

Further, the ECU 60 determines that the final fuel injection amount Q
INJ is set to an injection amount qinj (trt11map) determined based on the target throttle opening TRT (= trt11map). Here, the value of the injection amount qinj is a value that can ensure the same engine torque as during stratified combustion even during transient stratified combustion and can maintain the air-fuel ratio in a lean region based on experiments and the like. Is set. The ECU 60 once ends the process here.

Next, returning to step 110, EC
U60 indicates that the RS processing execution flag XRS is currently “ON”
Is described, and the process proceeds to step 210.

In step 210, the ECU 60
It is determined whether or not the value of the combustion mode instruction value fmode is “2”. If the ECU 60 determines that the value of the combustion mode instruction value fmode is currently “2”, the ECU 60 proceeds to FIG.
The process proceeds to step 310 shown in FIG. Here, EC
When U60 determines that the value of the combustion mode instruction value fmode is “2”, the timings t1 to t1 shown in FIG.
These are two sections between timing t2 and between timing t3 and timing t4.

On the other hand, if it is determined in step 210 that the value of the combustion mode instruction value fmode is not currently “2”, the ECU 60 shifts the processing to step 220. Here, the ECU 60 sets the combustion mode instruction value fmod.
The case where it is determined that the value of e is not “2” corresponds to the period between the timing t2 and the timing t3 shown in FIG. 6, and the value of the combustion mode instruction value fmode at this time is as shown in FIG. It becomes "11" (homogeneous rich combustion).

Hereinafter, first, at step 210, EC
U60 is the value of the combustion mode instruction value fmode is currently
Description will be made from the case where it is determined to be “2”. In step 310 shown in FIG. 5, the ECU 60 determines whether or not the count number of the fmode counter CNT2 has reached a predetermined number γ. Here, the predetermined number γ is for setting the length of the period for maintaining the combustion mode in the transitional stratified combustion, the retention period is sufficiently longer than the response delay time of the intake air amount, and The period is set so that the engine combustion state can be stabilized.

Therefore, the ECU 60 determines in step 31
If it is determined at 0 that the count number of the fmode counter CNT2 has not yet reached the predetermined number γ, the process is temporarily ended so as to further continue the transient stratified combustion. On the other hand, when determining that the count number of the fmode counter CNT2 has reached the predetermined number γ, the ECU 60 proceeds to step 320.

Then, in step 320, E
The CU 60 determines whether or not the count number of the catalyst counter CNT1 exceeds a predetermined number α. Catalyst counter CN
If it is determined that the count of T1 exceeds the predetermined number α, the process proceeds to step 330.

In step 330, the ECU 60
Resets the fmode counter CNT2 to zero and sets the value of the combustion mode instruction value fmode to "11" corresponding to homogeneous rich combustion. Also, the ECU 60
It instructs the catalyst counter CNT1 to switch from the addition operation to the subtraction operation. Furthermore, EC
U60 determines the final fuel injection amount QINJ (basic fuel injection amount Qbse × predetermined coefficient FR) in order to execute homogeneous rich combustion.
SPK). The injection amount (Qbse × FR
The value of (SPK) is set to a value that can obtain the same engine torque as during stratified combustion when the rich spike processing is started. Here, the ECU 60 once ends the processing.

On the other hand, if it is determined in step 320 that the count number of the catalyst counter CNT1 does not exceed the predetermined number α, it is determined that the combustion mode is to be switched from the stratified combustion in transition to the stratified combustion in transition, and the process proceeds to step 340. .

Then, in this step 340, E
The CU 60 resets the fmode counter CNT2 to zero, sets the value of the combustion mode instruction value fmode to “0” (stratified combustion), and further sets the RS execution flag XR
S is set to “OFF”. Then, the ECU 60 once ends the processing.

Now, description will return to step 210 shown in FIG. Step 2 as described above
In 10, the ECU 60 sets the combustion mode instruction value fmo
When it is determined that the value of de is not currently “2”, that is, the value of the combustion mode instruction value fmode is currently “1”.
1 ”(homogeneous rich combustion)
60 shifts the processing to step 220.

In step 220, the ECU 60
Determines whether the count number of the catalyst counter CNT1 has been reduced to a predetermined number β. When the ECU 60 determines in step 220 that the count number of the catalyst counter CNT1 has been reduced to the predetermined number β (timing t3 in FIG. 6), the ECU 60 shifts the processing to step 230 to end the homogeneous rich combustion.

In step 230, the ECU 60
Instruct the catalyst counter CNT1 to switch from the subtraction operation to the addition operation so far,
Instruct the mode counter CNT2 to start the addition operation. Further, the value of the combustion mode instruction value fmode is set to “2”.
And Further, the ECU 60 calculates the final fuel injection amount QINJ
To the injection amount qinj (trt11map) as in step 160
Set to. Then, the ECU 60 once ends the processing.

On the other hand, if it is determined in the previous step 220 that the count number of the catalyst counter CNT1 has not been reduced to the predetermined number β, the ECU 60 once terminates the processing to continue the homogeneous rich combustion.

According to the processing procedure described above, the ECU 6
0 indicates that when the rich spike processing is executed, the combustion mode instruction value fmode is changed from "0" (stratified combustion) to "2" (transient stratified combustion) → "11" (homogeneous rich combustion) → "2".
(Transitional stratified combustion) is sequentially switched from “0” (stratified combustion).

Next, the temporal transition of the combustion mode during the rich spike control process and the operation of the process will be described with reference to the timing chart shown in FIG. As shown in FIG. 6, at timing t1 when the count number of the catalyst counter CNT1 reaches the predetermined number α, the RS execution flag XRS (FIG. 6 (c)) is set to “ON” and the combustion mode instruction value is set. fmode (Fig. 6 (d))
Is changed from “0” to “2”, and the combustion mode is switched from stratified combustion to transient stratified combustion. At this time, f for counting the execution period (τ1) of the transient stratified combustion is used.
The mode counter CNT2 starts counting (FIG. 6B).

At this timing t1, the final fuel injection amount QINJ is increased and set to qinj (trt11map), which is the injection amount based on the target throttle opening TRT (= trt11map) during homogeneous rich combustion, as described above. (FIG. 6E). At this time, as described above, the air-fuel ratio remains in the lean region without any change in the engine torque.

The target throttle opening TRT is the target throttle opening TRT (= trt11ma) during homogeneous rich combustion.
It is set to a value reduced to p). The target exhaust gas recirculation valve opening EGR is also determined by the target throttle opening TR
With a decrease in T, the target exhaust gas recirculation valve opening EGR (= egr11map) is also set to a value reduced to the target exhaust gas recirculation valve opening during homogeneous rich combustion. And, these target throttle opening degrees T
The RT and the target exhaust gas recirculation valve opening EGR are not changed until the timing t4 (FIGS. 6F and 6F).
(G)).

With the decrease in the target throttle opening TRT, the intake pressure PM (FIG. 6 (h)) having a correlation with the intake air amount also decreases after the timing t1, but this intake pressure PM (the intake air amount ), The response delay (Δ) is compared with the change in the target throttle opening TRT as described above.
τ) exists. This is the target throttle opening TR
Even if the throttle valve 54 is changed by driving the throttle motor 54 based on T, until the opening of the throttle valve 34 becomes equal to the target throttle opening TRT, and the intake pressure PM becomes the target throttle opening TRT.
This is because a predetermined time is required until the size changes to a size corresponding to the above.

On the other hand, at the timing t1, the air-fuel ratio A /
The value of F once decreases rapidly with the increase in the final fuel injection amount QINJ, and then gradually decreases in response to a change in the intake air amount (intake pressure PM) (FIG. 6).
(I)).

Next, after the timing t1, the above fmod
At timing t2 when the count number of the e-counter CNT2 increases and reaches the predetermined number γ,
When a predetermined period τ1 determined by the predetermined number γ from 1 has elapsed, the combustion mode instruction value fmode is changed from “2” to “1”.
1 ", and the combustion mode is switched from the stratified combustion during the transition to the homogeneous rich combustion. At this time, as described above, the final fuel injection amount QINJ is determined by (basic fuel injection amount Qbse × predetermined coefficient FRSP) in order to execute homogeneous rich combustion.
K) is further increased (FIG. 6 (e)). Also,
The fuel injection mode is changed from the compression stroke injection to the intake stroke injection. Since the fuel injection mode is changed in this manner, the engine torque does not change even if the fuel injection amount is increased.

At this timing t2, the target throttle opening TRT and the target exhaust gas recirculation valve opening EG
The value of R is not changed. The predetermined period τ1 is set as a period longer than the response delay time (Δτ) of the intake pressure PM, and is set as a period during which the stability of the engine combustion mode with respect to the change in the final fuel injection amount QINJ can be ensured. .

As described above, in this embodiment, when the combustion mode is switched from the transitional stratified combustion to the homogeneous rich combustion at this timing t2, the final fuel injection amount QIN
Although J is increased, the intake air amount (intake pressure PM) is kept constant, so that the air-fuel ratio A / F depends on only the injection amount QINJ in the lean region without being affected by changes in the intake air amount. To the rich area quickly. Therefore, the air-fuel ratio A / F can pass near the stoichiometric air in a short time (FIG. 6 (i)).

As a result, when the air-fuel ratio passes near the stoichiometric ratio, it is possible to preferably suppress the NOx from being released from the NOx catalyst 24 without being purified. Further, since the combustion mode is switched so as not to cause a change in the engine torque, a shock during operation is suppressed.

Subsequently, after the timing t2, a predetermined period τ2
During this period, the combustion mode is set to the homogeneous rich combustion and the air-fuel ratio is kept rich, so that the NOx stored in the NOx catalyst 24 is reduced, and the stored amount gradually decreases. The operation amount of the count reduction by the catalyst counter CNT1 is set in advance based on experiments or the like such that the predetermined period τ2 is a period sufficient to reduce the occlusion amount of the NOx catalyst 24 to a predetermined lower limit amount. Have been.

Then, a predetermined period τ2 from the timing t2
Has elapsed, and at timing t3 when the count number of the catalyst counter CNT1 decreasing the count number reaches the predetermined number β (FIG. 6 (a)), the combustion mode instruction value fm
mode is changed from “11” to “2” again. Then, from this timing t3, the combustion mode is switched again to the transitional stratified combustion, and the continuation period (τ)
3) is counted by the fmode counter CNT2 (FIG. 6B).

At this timing t3, in order to switch the combustion mode from the homogeneous rich combustion to the transitional stratified combustion, the final fuel injection amount QINJ is changed to the injection amount qinj (trt).
11map). Therefore, at this timing t3
In FIG. 6, the value of the air-fuel ratio A / F shifts from the rich region to the lean region again only depending on the same injection amount QINJ (FIG. 6 (i)). At this time, the fuel injection mode is changed from the intake stroke injection to the compression stroke injection.

After the timing t3, a predetermined period τ3
(= Τ1) has elapsed and the above-mentioned fmode counter CNT
At the timing t4 when the count number of the “2” reaches the predetermined number γ (FIG. 6B), the RS execution flag XRS becomes “OF”.
F "(FIG. 6 (c)), and the combustion mode is switched from stratified combustion to stratified combustion in transition.

At this timing t4, the final fuel injection amount QINJ is changed from the injection amount qinj to the basic fuel injection amount Qb.
The fuel injection amount is further reduced to se and returned to the injection amount immediately before the timing t1 (FIG. 6 (e)), and the target throttle opening TRT and the target exhaust gas recirculation valve opening EGR are each immediately before the timing t1. It is returned to the opening. Thereafter, the value of the air-fuel ratio A / F returns to the value before the execution of the rich spike processing in a form corresponding to the intake air amount (intake pressure PM) (FIG. 6 (i)).

As described in detail above, according to the present embodiment, the following effects can be obtained. (1) When the combustion mode is switched from stratified combustion to homogeneous rich combustion by the rich spike processing, the air-fuel ratio A / F
Is the injection quantity QIN without being affected by changes in the intake air quantity.
The transition from the lean region to the rich region depends on J alone. That is, the air-fuel ratio A / F can pass in the vicinity of the stoichiometric air in a short time. As a result, when the air-fuel ratio passes near the stoichiometric ratio, it is also possible to preferably suppress the NOx from being released from the NOx catalyst 24 without being purified, and to suppress the deterioration of the NOx emission.

(2) During execution of the rich spike processing, the combustion mode is switched so that the engine torque is kept constant, so that the operational shock accompanying the rich spike processing is also suitably suppressed.

(3) According to the present embodiment, the predetermined period τ1 during which the stratified combustion during the transition period is continued is set as a period longer than the change time Δτ of the intake pressure PM, and the change in the final fuel injection amount QINJ is changed. Is set as a time during which the stability of the engine combustion state associated with the above can be secured. Therefore, when the combustion mode is switched from stratified combustion to homogeneous rich combustion, the effect of the change in the intake air amount on the change in the air-fuel ratio A / F is reliably eliminated, and the effect of the above (1) is further ensured. In addition, the effect of the rich spike processing on the engine combustion state can be further reduced.

The above embodiment can be modified, for example, as follows. In the above embodiment, the combustion mode instruction value fmo
de switching ("0" → "2" → "11" → "2" →
"0"), the catalyst counter CNT1 and fmode
Although the example in which the counter CNT2 is used and the count is performed based on the predetermined count number has been described, the combustion mode instruction value fmod
The switching mode of e is not limited to those using these counters. For example, the fmode may be switched based on the detection result of the NOx concentration in the exhaust gas.

Also, even when the combustion mode instruction value fmode is switched using a counter as in the above embodiment, the usage of the counter is as follows.
It is not limited to the above embodiment. For example, the instruction value fmode may be switched using one counter, or three counters may be used. Also, instead of performing the processing related to the determination in step S320 shown in FIG. 5 based on the count number α of the catalyst counter CNT1, for example, the timing t
A NOx occlusion flag or the like that is set to “OFF” in 3 may be set, and the determination may be made based on the flag.

In the above-described embodiment, the target throttle opening TRT and the target exhaust gas recirculation valve opening EGR are changed during the rich spike processing. It may be omitted.

In the above embodiment, the duration (execution period) τ3 of the transient stratified combustion executed after the homogeneous rich combustion is changed to the execution period τ1 of the transient stratified combustion executed before the homogeneous rich combustion. It may be shorter. This is because, as shown in FIG. 6, the execution period τ3 does not include the response delay time Δτ of the intake pressure PM, so that the execution period τ3 can be shortened. By thus shortening the execution period τ3, the time required for the rich spike processing can be reduced.

The execution period τ1 of the transitional stratified combustion determined by the predetermined number γ is determined according to the change amount ΔTRT (trt0map-trt11map) of the target throttle opening TRT when the combustion mode is switched from the stratified combustion to the homogeneous rich combustion. You may make it variably set. Thus, the same variation ΔTR
By making the execution period τ1 of the stratified combustion during transition variable according to T, for example, if the same change ΔTRT is large, the period τ1 is set long, and if the same change ΔTRT is small, the period τ1 is changed. By setting to be short, it is possible to more suitably reduce the influence of the rich spike processing on the engine combustion state, and it is also possible to optimize the time required for the rich spike processing.

In the above embodiment, in the post-processing after the completion of the homogeneous rich combustion, the stratified combustion is switched to the stratified combustion via the transient stratified combustion (fmode “2”). It is also possible to switch to stratified combustion immediately without going through combustion (fmode "2").

In the above embodiment, the execution period τ1 of the transient stratified combustion is set to be longer than the response delay time Δτ of the intake pressure PM.
Not limited to this. For example, the execution period τ1 may be equal to or shorter than the response delay time Δτ.

In the above-described embodiment, the combustion control device of the present invention is applied to the engine 10 in which stratified charge combustion and homogeneous stoichiometric combustion are selected as normal combustion modes. The present invention can be similarly applied to an engine in which a combustion mode such as stratification intensity is made weaker than stratification combustion by using both compression stroke injection and intake stroke injection) or homogeneous lean combustion is selected.

Finally, technical ideas other than the claims that can be grasped from the above-described embodiment will be described below together with their effects. (1) In the combustion control device for an internal combustion engine according to claim 2, the switching means sets the throttle opening degree when the execution period is switched from stratified combustion to homogeneous rich combustion. A combustion control device for an internal combustion engine, which is variably set according to a change amount. According to the configuration, for example, when the amount of change in the set value of the throttle opening is large, the execution period is set long, and conversely, when the amount of change is small, the period of synchronization is set short. The effect of the spike processing on the combustion state of the engine can be further reduced, and the time required for the rich spike processing can be optimized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a configuration of an embodiment in which a combustion control device for an internal combustion engine according to the present invention is applied to a combustion control device for an engine.

FIG. 2 is a graph showing a structure of a map referred to when calculating a basic fuel injection amount.

FIG. 3 is a graph showing the structure of a map referred to when switching the combustion mode.

FIG. 4 is a flowchart illustrating a processing procedure of rich spike control.

FIG. 5 is a flowchart illustrating a processing procedure of rich spike control.

FIG. 6 is a timing chart showing an example of a temporal transition of rich spike control.

FIG. 7 is a timing chart showing a temporal transition of an air-fuel ratio according to a change in a throttle valve opening;

[Explanation of symbols]

10 engine, 11 cylinder block, 12 cylinder head, 13 piston, 14 crankshaft, 15 cylinder, 16 connecting rod, 1
7: combustion chamber, 18: intake port, 19: exhaust port, 2
0: intake pipe, 21: exhaust pipe, 22: surge tank, 24
... NOx catalyst, 26 ... Spark plug, 30, 31 ... Cam shaft, 34 ... Throttle valve, 42 ... EGR passage,
43 EGR valve, 43a Step motor, 46
Accelerator pedal, 50 injector, 53 ignition coil, 54 throttle motor, 60 ECU, 61 memory, 64 accelerator sensor, 65 crank sensor,
66: cam sensor, 67: intake pressure sensor.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/04 335 F02D 41/04 335B 43/00 301 43/00 301H 301J 301K 45/00 312 45/00 312A F-term (reference) 3G065 CA12 CA13 DA05 FA04 FA12 GA01 GA10 GA41 GA46 KA36 3G084 AA04 BA05 BA09 BA13 BA15 BA20 DA10 DA11 EA11 EB08 EB12 EB24 EC02 EC03 FA10 FA11 FA33 FA37 FA38 3G301 HA04 HA13 MA03 MA04 JA03 MA04 NA08 NC02 NC08 ND01 NE01 NE13 NE23 PA07Z PA11A PA11Z PA12Z PD15A PE01Z PE03Z PF03Z

Claims (2)

[Claims] 1. A stratified charge combustion is executed as a form of directly injecting fuel into a cylinder during a compression stroke, and a homogeneous rich combustion is executed as a form of injecting fuel during an intake stroke. In a combustion control device for an internal combustion engine, when switching from stratified combustion to homogeneous rich combustion so that engine torque is constant, the throttle opening is set to the opening required for homogeneous rich combustion without changing the fuel injection mode An internal combustion engine having a switching means for temporarily executing a combustion mode for controlling the fuel injection amount in accordance with the set throttle opening, and then changing the fuel injection mode and switching the combustion mode to homogeneous rich combustion. Engine combustion control device. 2. A combustion control apparatus for an internal combustion engine according to claim 1, wherein said switching means sets a throttle opening to an opening required for homogeneous rich combustion without changing said fuel injection mode. The execution period of the combustion mode in which the injection amount is controlled in accordance with the set throttle opening is set to a period longer than a response delay period of a change in intake air amount of the engine accompanying the setting of the throttle opening. Control device for an internal combustion engine.