JP2003314314A - Internal combustion engine control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To switch combustion mode in a shorter time than a current one, while maintaining combustion safety when switching the combustion mode of a cylinder-inside injection engine. <P>SOLUTION: When a request to switch the combustion mode for a short time to purge NOx from the NOx catalyst is detected during the stratified charge combustion mode operation of the cylinder-inside injection engine, operation mode is temporarily switched to a homogeneous combustion mode. Intake valve timing (intake VCT) and exhaust valve timing (exhaust VCT) as control parameters having a large response delay among control parameters of a pneumatic system are fixed to a target value of the stratified charge combustion mode as a combustion mode before switching the operation mode, and the only other control parameter (throttle opening, EGR valve, an air flow control valve) of the pneumatic system are immediately switched to a target value of the homogeneous combustion mode as a combustion mode after switching the operation mode. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine control device for switching a combustion mode between a stratified combustion mode and a homogeneous combustion mode according to an operating state of an internal combustion engine.

[0002]

2. Description of the Related Art In recent years, the demand for in-cylinder injection engines having the features of low fuel consumption, low exhaust emission and high output has been rapidly increasing. This in-cylinder injection engine injects a small amount of fuel in the compression stroke at low load to perform stratified combustion of the air-fuel mixture (lean operation), and at high load, increases the fuel injection amount and injects it in the intake stroke to produce the air-fuel mixture. Burn homogeneously (rich operation).
Further, since the in-cylinder injection engine produces a larger amount of NOx than a general intake port injection engine, NOx is discharged to the exhaust pipe.
A storage-reduction type NOx catalyst is often installed.

This NOx catalyst adsorbs NOx in the exhaust gas during stratified combustion operation (during lean operation) in which the oxygen concentration in the exhaust gas is high, and then switches to homogeneous combustion operation (rich operation) and exhausts. When the oxygen concentration in the inside decreases, the adsorbed NOx is reduced and purified and released. Therefore,
In order to maintain the NOx purification performance of the NOx catalyst, the NOx is sometimes switched to the homogeneous combustion operation during the stratified charge combustion operation.
It is necessary to perform NOx purging of the catalyst.

Further, during the stratified charge combustion operation, the throttle opening is kept fully open, so that the negative pressure in the intake pipe is small and the braking boosting effect of the brake booster using the negative pressure as a drive source is reduced. Therefore, during the stratified charge combustion operation, it is necessary to occasionally switch to the homogeneous combustion operation to increase the intake pipe negative pressure to secure the negative pressure in the brake booster.

For the above reasons, in the cylinder injection engine, the combustion mode is appropriately switched between stratified combustion and homogeneous combustion during operation. At this time, Patent No. 32
As shown in Japanese Patent Publication No. 01936, the target values of the control parameters of the air system, the fuel system, and the ignition system are set for each combustion mode by a map or the like, and when switching the combustion mode, the air system,
Each control parameter of the fuel system and the ignition system is switched to the target value of the combustion mode of the switching destination.

[0006]

However, as shown in FIG. 8A, in the conventional cylinder injection engine, the exhaust gas recirculation control valve (EGR valve) is opened to recirculate the exhaust gas into the cylinder. Since there is a region where combustion becomes unstable between the stable combustion regions of both stratified combustion and homogeneous combustion, the region passes through the unstable combustion region when switching the combustion mode. For this reason,
Depending on the load when switching the combustion mode, there is a risk that misfire or torque shock may occur when passing through the unstable combustion region.

In addition, in-cylinder injection engines of recent years are
New functions such as variable valve timing mechanism and variable valve lift mechanism have been added to the air system to further improve exhaust emission and output, and the number of air system control parameters will continue to increase. It seems to be.
However, as the number of air system control parameters increases,
The influences of each control parameter are complicatedly entangled, and the intake air amount (cylinder filling air amount), the cylinder air flow state, the external exhaust gas recirculation amount (external EGR amount), the internal exhaust gas recirculation amount (internal EGR amount)
However, in order to switch the combustion mode while maintaining combustion stability, it is necessary to slow down the switching speed of the combustion mode to allow a certain time margin for switching each control parameter. There is a new drawback that the mode switching control becomes slow. Moreover, if the number of control parameters to be switched increases, the number of matching man-hours required to create a switching map for each control parameter at the vehicle development and design stage becomes enormous, and the vehicle development and design period becomes long.

The above-mentioned problems at the time of switching the combustion mode are not only problems of the cylinder injection engine, but even the intake port injection engine has the function of switching the combustion mode like the lean burn engine. If so, there is a similar problem.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an internal combustion engine equipped with many functions even if the combustion mode is maintained while maintaining the combustion stability. Can be switched in a shorter time than before, and the switching speed of the combustion mode can be increased,
An object of the present invention is to provide an internal combustion engine control device capable of reducing the number of control parameter adaptation steps in the vehicle development and design stage and shortening the vehicle development and design period.

[0010]

In order to achieve the above object, an internal combustion engine control apparatus according to a first aspect of the present invention is arranged such that when a combustion mode switching request is made, the internal combustion engine control apparatus other than the throttle opening degree of the air system. At least one control parameter (hereinafter referred to as "specific control parameter") is fixed and a specific control parameter fixed combustion mode switching control for switching the combustion mode is executed. Since each control parameter of the air system is complicatedly intertwined with each other, the intake air amount (cylinder filling air amount), the air flow state in the cylinder, the external exhaust gas recirculation amount, and the internal exhaust gas recirculation amount are complicatedly changed. When the number of air system control parameters increases, in order to switch combustion modes while maintaining combustion stability, it is necessary to slow down the combustion mode switching speed and allow a certain amount of time to switch each control parameter. However, there is a drawback that the number of man-hours required to create a switching map for each control parameter at the vehicle development and design stage becomes enormous.

Therefore, if at least one control parameter (specific control parameter) of the air system control parameters is fixed when the combustion mode is switched as in the present invention, the number of control parameters that need to be switched is reduced. Therefore, switching control of the air system control parameters becomes easier than switching all the air system control parameters, and combustion mode switching speed can be increased while maintaining combustion stability during combustion mode switching. It is possible to reduce the number of control parameter adaptation steps in the vehicle development and design stage, and to shorten the vehicle development and design period.

According to a second aspect of the present invention, an intake valve varying means for varying the intake valve timing and / or the intake valve lift amount by the air system, and an exhaust valve for varying the exhaust valve timing and / or the exhaust valve lift amount. It may be applied to an internal combustion engine provided with at least one of the variable means, the exhaust gas recirculation control means for controlling the exhaust gas recirculation amount, and the air flow control means for controlling the air flow in the cylinder. When switching the combustion mode,
This is because it is difficult to switch all these control parameters in a short time without deteriorating the combustion state.

Further, as in claim 3, when the combustion mode is temporarily switched for a short time, the specific control parameter fixed combustion mode switching control may be executed. For example, when performing lean operation in the stratified charge combustion mode and performing NOx purging of the NOx catalyst or securing a negative pressure in the brake booster, it is only necessary to temporarily switch the combustion mode to the homogeneous combustion mode, Since the time of homogeneous combustion mode (rich operation) is very short, even if the combustion mode is switched by fixing certain control parameters,
Before the effect appears, the original combustion mode can be restored, and combustion stability can be maintained.

Further, as in the fourth aspect, the specific control parameter fixed at the time of switching the combustion mode may be a control parameter having a large variation in response compared with other control parameters. Even if the control parameter having a large variation in responsiveness is switched in synchronization with the combustion mode switching request, the responsiveness varies for each combustion mode switching request. Therefore, if the combustion mode is switched in a short time, the influence on the air system does not differ much even if the control parameters having large variations in response are fixed or switched. Therefore, if the specific control parameter fixed at the time of switching the combustion mode is a control parameter having a large variation in responsiveness, the effect of fixing the control parameter can be reduced.

In this case, the control parameter, which is fixed when the combustion mode is switched and has a large variation in response, may be the valve timing and / or the valve lift amount on the intake side and / or the exhaust side. Generally, the valve timing and the valve lift amount are controlled by the hydraulic pressure, so that the responsiveness varies widely, and the viscosity (fluidity) of the hydraulic oil changes depending on the oil temperature, and the hydraulic pressure fluctuates. Since the hydraulic pressure fluctuates, the control accuracy is poor compared to other control parameters. Therefore, if the combustion mode is switched in a short time, even if the valve timing and the valve lift amount are fixed, there is little effect, and depending on the engine operating condition, it is better to fix the valve timing and the valve lift amount for stable combustion. In some cases, it is easy to maintain sex.

Further, as in claim 6, the specific control parameter may be fixed until the combustion mode is returned to the original combustion mode after the specific control parameter fixed combustion mode switching control is started. In this way, the combustion mode switching control becomes easy.

In this case, when the specific control parameter fixed combustion mode switching control is started as in claim 7, the specific control parameter is fixed to the target value of the combustion mode immediately before it, or As in the item 8, when the specific control parameter fixed combustion mode switching control is started, the specific control parameter may be fixed to the target value for switching the combustion mode. The former (claim 7) has the advantage of facilitating the combustion mode switching control because it is not necessary to change the specific control parameter before and after the combustion mode switching. On the other hand, when the specific control parameter is fixed to the target value of the combustion mode before switching, when the deterioration of combustion stability is concerned, as in the latter case (claim 8),
If the specific control parameter is fixed to the target value for switching the combustion mode, there is an advantage that the combustion stability during the combustion mode switching control can be secured.

Although the present invention can be applied to a lean burn engine, as in claim 9, it is applied to a cylinder injection type internal combustion engine to request NOx purging of a NOx catalyst or securing a negative pressure in a brake booster. If there is, it is preferable to execute the specific combustion control parameter fixed combustion mode switching control. With this configuration, the NOx purge control and the control for securing the negative pressure in the brake booster can be executed in a shorter time than before while maintaining the combustion stability, and the drivability and the fuel consumption can be improved.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a cylinder injection type internal combustion engine will be described below with reference to the drawings.
First, the schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner 13 is provided at the most upstream portion of an intake pipe 12 of a cylinder injection type engine 11 which is a cylinder injection type internal combustion engine, and an air flow meter 14 for detecting an intake air amount is provided on the downstream side of the air cleaner 13. It is provided. On the downstream side of this air flow meter 14,
A throttle valve 16 driven by a motor 15 such as a DC motor is provided, and the opening of the throttle valve 16 (throttle opening) is detected by a throttle opening sensor 17.

A surge tank 18 is provided on the downstream side of the throttle valve 16.
8, an intake pipe pressure sensor 19 for detecting the intake pipe pressure is provided. Further, the surge tank 18 is provided with an intake manifold 20 for introducing air into each cylinder of the engine 11, and the intake manifold 20 of each cylinder controls an air flow (a swirl flow or a tumble flow) in the cylinder of the engine 11. An airflow control valve 31 is provided.

A fuel injection valve 21 for directly injecting fuel into each cylinder is attached to an upper portion of each cylinder of the engine 11. A spark plug 22 is attached to the cylinder head of the engine 11 for each cylinder.
The spark discharge of 2 ignites the mixture in the cylinder. Further, the intake valve 37 and the exhaust valve 38 of the engine 11 have variable valve timing mechanisms 39 and 40 (intake / exhaust valve varying means) for varying the valve timing, respectively.
Is provided.

A knock sensor 32 for detecting knocking, a cooling water temperature sensor 23 for detecting cooling water temperature, and a crank angle sensor 24 for detecting engine rotation speed are attached to a cylinder block of the engine 11.

On the other hand, the exhaust pipe 25 of the engine 11 is provided with an upstream side catalyst 26 and a downstream side catalyst 27 for purifying exhaust gas, and an exhaust gas air-fuel ratio or lean / rich is provided upstream of the upstream side catalyst 26. Exhaust gas sensor 28 for detecting etc.
(Air-fuel ratio sensor, oxygen sensor, etc.) are provided. In the present embodiment, a three-way catalyst that purifies CO, HC, NOx, etc. in the exhaust gas near the stoichiometric air-fuel ratio is provided as the upstream side catalyst 26, and a NOx catalyst (NOx) as the downstream side catalyst 27.
A storage reduction catalyst) is provided. This NOx catalyst 2
No. 7 has a characteristic of storing NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is lean, and reducing and purifying the stored NOx when the air-fuel ratio is near the stoichiometric air-fuel ratio or becomes rich. .

The upstream side catalyst 26 in the exhaust pipe 25
An EGR pipe 33 for recirculating a part of the exhaust gas to the intake side is connected between the downstream side of the exhaust gas and the surge tank 18 of the intake pipe 12 downstream of the throttle valve 16.
An EGR valve 34 (exhaust gas recirculation control means) for controlling the exhaust gas recirculation amount (EGR amount) is provided in the middle of the EGR pipe 33. Further, the depression amount of the accelerator pedal 35 is detected by the accelerator sensor 36.

The outputs of the various sensors described above are input to an engine control circuit (hereinafter referred to as "ECU") 30. The ECU 30 is mainly composed of a microcomputer, and executes various control routines stored in a built-in ROM (storage medium), so that the fuel injection amount and the fuel of the fuel injection valve 21 are changed according to the engine operating state. The injection timing, the ignition timing of the spark plug 22 and the like are controlled.

This ECU 30 will be described later with reference to FIGS.
By executing each routine shown in (1), the stratified combustion mode and the homogeneous combustion mode are switched according to the engine operating state (requested torque, engine speed, etc.). In the stratified charge combustion mode, a small amount of fuel is directly injected into the cylinder in the compression stroke to form a stratified mixture near the ignition plug 22 for stratified charge combustion, thereby improving fuel efficiency. On the other hand, in the homogeneous combustion mode, the engine output is increased by increasing the fuel injection amount and directly injecting it into the cylinder in the intake stroke to form a homogeneous mixture for homogeneous combustion. Further, when the stratified combustion mode is switched to the homogeneous combustion mode, the EGR valve 34 is switched to the fully closed state to expand the stable combustion region of both the stratified combustion and the homogeneous combustion as shown in FIG. 8 (b). Then,
After the unstable combustion region as shown in (a) is eliminated (or reduced), the stratified combustion mode is switched to the homogeneous combustion mode.

Further, the ECU 30 functions as the control means in the claims, and N during the stratified charge combustion mode operation.
When there is a short-time (for example, several seconds or less) combustion mode switching request for NOx purging of the Ox catalyst 27 or securing a negative pressure in the brake booster, the homogeneous combustion mode is temporarily switched for a short time. At this time, the combustion mode is changed from the stratified combustion mode by fixing at least one control parameter (specific control parameter) other than the throttle opening degree of the air system to the target value of the stratified combustion mode which is the combustion mode before switching. Switch to homogeneous combustion mode.

At this time, the control parameter of the air system to be fixed is a control parameter having a large response delay compared to other control parameters, and specifically, the intake valve timing (hereinafter referred to as "intake VCT"). And exhaust valve timing (hereinafter referred to as "exhaust VCT"). Other control parameters of the air system (throttle valve 16, EGR valve 34, air flow control valve 31 in the present embodiment) are set to the combustion mode of the switching destination immediately when there is a short-time combustion mode switching request. Switch to the target value of the mode. Hereinafter, the control for fixing the intake / exhaust VCT and switching the other control parameters of the air system is referred to as "VCT fixed combustion mode switching control".

In the stratified charge combustion mode, the intake / exhaust VCT is controlled by a gas for forming a stratified mixture in the cylinder by reducing valve overlap as shown in FIG. 9 (a). Make it easier for flow (swirl or tumble flow) to occur. Further, in the normal homogeneous combustion mode, as shown in FIG. 9B, the valve overlap is increased to increase the internal EGR, and the N in the exhaust gas is increased.
Ox and HC are reduced, and pump loss is reduced to improve fuel efficiency.

During operation in the stratified combustion mode, the NOx catalyst 27
When there is a short-time combustion mode switching request for NOx purging of NOx, securing a negative pressure in the brake booster, etc., the above-mentioned VCT fixed combustion mode switching control is executed to perform intake V
The CT and the exhaust VCT are fixed to the target values of the stratified combustion mode which is the combustion mode before switching, and only the other control parameters of the air system are immediately switched to the target values of the homogeneous combustion mode which is the combustion mode of the switching destination (Fig. 11).

When the engine operating state (requested torque, engine speed, etc.) changes and a combustion mode switching request is generated during engine operation, VCT fixed combustion mode switching control is not performed and intake / exhaust VCT is not performed. Immediately, all the control parameters of the air system including are switched to the target value of the combustion mode of the switching destination.

On the other hand, the control parameters of the fuel system and the ignition system are not changed before the actual combustion state of the air system is changed to the normal combustion state in the combustion mode of the switching destination even when the combustion mode switching request is made. The target value of the combustion mode of is maintained. After that, when the actual state of the air system becomes a state where normal combustion is possible in the combustion mode of the switching destination, the control parameters of the fuel system and the ignition system are switched to the target values of the combustion mode of the switching destination. This completes the switching of the actual combustion mode.

The above-described combustion mode switching control of this embodiment is executed by the ECU 30 in accordance with the routines shown in FIGS. The processing contents of each of these routines will be described below.

[Engine Control Main Routine] The engine control main routine of FIG. 2 is executed at a predetermined cycle after the ignition switch (not shown) is turned on. When the main routine is started, first, at step 100, the required torque is calculated based on the accelerator opening, the engine speed, and the like. After that, the routine proceeds to step 200, where the combustion mode determination routine of FIG. 3 is executed to determine the combustion mode, and then the routine proceeds to step 300, where the combustion mode switching control routine of FIG. For example, the combustion mode switching control is executed, and the next steps 400 to 60
5, the air system control routine of FIG. 5, the fuel system control routine of FIG. 6, and the ignition system control routine of FIG. 7 are executed to switch the control parameters of the air system, the fuel system, and the ignition system at the timing described later. The combustion mode is switched by switching to the target value of the combustion mode.

[Combustion Mode Determination Routine] When the combustion mode determination routine of FIG. 3 is started in step 200 of the engine control main routine of FIG.
In 1, the required combustion mode determination map is searched to find the current engine operating state (eg engine speed and required torque).
Either the stratified combustion mode or the homogeneous combustion mode is selected as the required combustion mode in accordance with the above. In this required combustion mode determination map, in the low rotation speed and low torque region, the stratified combustion mode is selected with priority on fuel consumption reduction, while at the high rotation speed,
In the high torque region, the engine output is prioritized so that the homogeneous combustion mode is selected.

After that, the routine proceeds to step 202, where it is judged whether or not the required combustion mode selected according to the current engine operating state is the homogeneous combustion mode. If the required combustion mode is the homogeneous combustion mode, then step 203 Then, it is determined whether the current actual combustion mode is the homogeneous combustion mode. If the current actual combustion mode is not the homogeneous combustion mode, it is necessary to switch the combustion mode, so the routine proceeds to step 204, where the combustion mode switching flag is turned on,
Proceeding to step 205, the air system control mode is set to the homogeneous combustion mode. On the other hand, if the current actual combustion mode is the homogeneous combustion mode, it is not necessary to switch the combustion mode. Therefore, step 204 is skipped and the process proceeds to step 205 to maintain the air system control mode in the homogeneous combustion mode.

If it is determined in step 202 that the required combustion mode is not the homogeneous combustion mode (stratified combustion mode), the routine proceeds to step 206, where a short-time combustion mode switching request (for example, NOx purge of the NOx catalyst 27) is performed. And the requirement for ensuring negative pressure in the brake booster). As a result, when it is determined that there is a short-time combustion mode switching request, steps 203 to 2 described above are performed.
If the current actual combustion mode is the stratified combustion mode, the combustion mode switching flag is turned on (step 204), and the air system control mode is set to the homogeneous combustion mode (step 205).

On the other hand, when it is determined that the required combustion mode is the stratified combustion mode and there is no request for switching the combustion mode for a short time (both "No" in steps 202 and 206).
If it is determined that), the process proceeds to step 207, and it is determined whether the current actual combustion mode is the stratified combustion mode. If the current actual combustion mode is not the stratified combustion mode, it is necessary to switch the combustion mode, so the routine proceeds to step 208, where the combustion mode switching flag is turned ON,
Proceeding to step 209, the air system control mode is set to the homogeneous combustion mode. On the other hand, if the current actual combustion mode is the stratified charge combustion mode, it is not necessary to switch the combustion mode, so the process skips step 208 and proceeds to step 205 to maintain the air system control mode to the stratified charge combustion mode.

[Combustion Mode Switching Control Routine] When the combustion mode switching control routine of FIG. 4 is started in step 300 of the engine control main routine of FIG. 2, first, in step 301, the combustion mode switching flag is ON. Whether or not the combustion mode is being switched depending on whether
If the combustion mode is not being switched, this routine is ended without performing the subsequent processing.

On the other hand, if the combustion mode is being switched, the routine proceeds to step 302, where it is determined whether the required combustion mode is the stratified combustion mode. If the required combustion mode is not the stratified combustion mode (that is, the required combustion mode is If the actual air-fuel ratio A / F is in the homogeneous combustion region depending on whether the actual air-fuel ratio A / F is richer than the homogeneous combustion region determination value CAF2 or not (if it is in the homogeneous combustion mode). To judge. As a result, the actual air-fuel ratio A / F is equal to the homogeneous combustion region determination value CAF2.
If it is determined to be leaner (the actual air-fuel ratio A / F is not within the homogeneous combustion region), this routine is terminated without performing the subsequent processing.

Thereafter, when it is determined that the actual air-fuel ratio A / F becomes richer than the homogeneous combustion region determination value CAF2 and the actual air-fuel ratio A / F enters the region where homogeneous combustion is possible, the routine proceeds to step 304, After the fuel system control mode is set to the homogeneous combustion mode and the fuel injection mode is switched to the intake stroke injection, the combustion mode switching flag is turned off and this routine ends.

If it is determined that the combustion mode is being switched and the required combustion mode is the stratified combustion mode (if Yes in both steps 301 and 302), the process proceeds to step 306. Whether or not the air-fuel ratio A / F is leaner than the stratified combustion region determination value CAF1,
It is determined whether the actual air-fuel ratio A / F is in the stratified charge combustion region. As a result, the actual air-fuel ratio A / F becomes the stratified combustion region determination value C.
When it is determined that the air-fuel ratio is richer than AF1 (the actual air-fuel ratio A / F is not within the stratified charge combustion region), this routine is ended without performing the subsequent processing.

Thereafter, when it is determined that the actual air-fuel ratio A / F becomes leaner than the stratified combustion region determination value CAF1 and the actual air-fuel ratio A / F enters the region where stratified combustion is possible, the routine proceeds to step 308. After the fuel system control mode is set to the stratified combustion mode and the fuel injection mode is switched to the compression stroke injection, the combustion mode switching flag is turned off and this routine is ended.

[Air System Control Routine] When the air system control routine of FIG. 5 is started in step 400 of the engine control main routine of FIG. 2, first, in step 401, a short-time combustion mode switching request (for example, NOx catalyst is requested). 27 N
(Requirements such as Ox purging and securing negative pressure in the brake booster)
It is determined whether or not there is. As a result, if it is determined that there is no short-time combustion mode switching request, step 402
Then, it is determined whether the air system control mode is the homogeneous combustion mode. If it is the homogeneous combustion mode, step 403
Then, the target value for the homogeneous combustion mode is calculated as the target value of each control parameter of the air system (throttle valve 16, EGR valve 34, air flow control valve 31, intake VCT, exhaust VCT). If it is determined in step 402 that the air system control mode is not the homogeneous combustion mode (that is, the stratified charge combustion mode), the process proceeds to step 404, where the target value for each control parameter of the air system is the stratified charge combustion mode. Calculate the target value of.

On the other hand, when it is determined in step 401 that there is a short-time combustion mode switching request, the routine proceeds to step 405, where a target value for VCT fixed combustion mode switching control is calculated. The target value for the VCT fixed combustion mode switching control continues to maintain the target value for the intake / exhaust VCT in the stratified combustion mode, which is the combustion mode before switching, and the other target parameters for the air system (throttle valve 16, EGR). Only for the valve 34 and the air flow control valve 31), the target value of the homogeneous combustion mode which is the combustion mode of the switching destination is calculated.

[Fuel System Control Routine] When the fuel system control routine of FIG. 6 is started in step 500 of the engine control main routine of FIG. 2, first, in step 501, is the fuel system control mode a homogeneous combustion mode? It is determined whether or not, and if the homogeneous combustion mode, proceed to step 502,
Fuel system control parameters (fuel injection amount, fuel injection timing)
The target value for the homogeneous combustion mode is calculated as the target value of.

If it is determined in step 501 that the fuel system control mode is not the homogeneous combustion mode (that is, the stratified charge combustion mode), the process proceeds to step 503, where stratified charge combustion is set as the target value of the fuel system control parameter. Calculate the target value for the mode.

[Ignition System Control Routine] When the ignition system control routine of FIG. 7 is started in step 600 of the engine control main routine of FIG. 2, first in step 601, the ignition system control mode is the homogeneous combustion mode. If it is a homogeneous combustion mode, the process proceeds to step 602,
As the target value of the control parameter (ignition timing) of the ignition system,
Calculate the target value for homogeneous combustion mode.

If it is determined in step 601 that the ignition system control mode is not the homogeneous combustion mode (that is, the stratified combustion mode), the routine proceeds to step 603, where stratified charge combustion is set as the target value of the ignition system control parameter. Calculate the target value for the mode.

Differences between the combustion mode switching control of the present embodiment described above and the conventional combustion mode switching control are shown in FIG.
0 and the time chart of FIG. 11 will be described. Figure 1
0 is a time chart showing an example of the combustion mode switching control when there is a short-time combustion mode switching request (request for NOx purging of the NOx catalyst) in the conventional in-cylinder injection engine, and FIG. 11 is the present embodiment. 3 is a time chart showing an example of combustion mode switching control when there is a short-time combustion mode switching request in FIG.

In the conventional in-cylinder injection engine, as shown in FIG. 10, a short-time combustion mode switching request (a request such as NOx purging of the NOx catalyst) is generated during the stratified combustion mode operation, and the required combustion mode is stratified. Immediately after the combustion mode is switched to the homogeneous combustion mode, the target values of all control parameters (throttle opening, EGR valve, intake VCT, exhaust VCT, airflow control valve) of the air system are simultaneously switched to the combustion mode. Switch to the target value for homogeneous combustion mode. As described above, when the number of control parameters of the air system that are switched at the same time is large, the influences of the control parameters are intricately entangled with each other, and the intake air amount (cylinder filling air amount), the air flow state in the cylinder, the external EGR amount, the internal Since the EGR amount changes intricately, the time A required for the actual air-fuel ratio A / F to change from the stratified combustion region to the homogeneous combustion region determination value CAF2 becomes long. When the actual air-fuel ratio A / F changes to the homogeneous combustion region determination value CAF2, the fuel injection mode is switched to the intake stroke injection and the actual combustion mode is switched to the homogeneous combustion mode. Therefore, the actual air-fuel ratio A / F is changed to the stratified combustion region. If the time A required to change from the NOx to the homogeneous combustion region determination value CAF2 becomes long, a short-time combustion mode switching request (NOx of NOx catalyst NOx).
There is a problem that the time A from the occurrence of a request such as purging) to the switching of the actual combustion mode to the homogeneous combustion mode becomes long, and the switching speed of the combustion mode becomes slow. afterwards,
The same problem occurs when the actual combustion mode is switched from the homogeneous combustion mode to the stratified combustion mode.

On the other hand, in this embodiment, as shown in FIG. 11, a short-time combustion mode switching request (a request for NOx purging of the NOx catalyst, etc.) is generated during the stratified combustion mode operation, and the required combustion mode is set. When the stratified combustion mode is switched to the homogeneous combustion mode, the combustion mode switching flag is turned on.
To perform the VCT fixed combustion mode switching control, fix the intake VCT and the exhaust VCT to the target value of the stratified combustion mode which is the combustion mode before switching, and control other air system control parameters (throttle opening, throttle opening, EGR valve 3
4. Only the air flow control valve 31) is immediately switched to the target value of the homogeneous combustion mode which is the combustion mode of the switching destination.

Then, when the actual air-fuel ratio A / F changes to the homogeneous combustion region determination value CAF2, the combustion mode switching flag is switched to OFF, the fuel injection mode is switched to the intake stroke injection, and the actual combustion mode is homogeneously combusted. Switch to mode. Even after this, the intake VCT and the exhaust VCT are maintained in a state of being fixed to the target value of the stratified combustion mode which is the combustion mode before switching.

After that, when the required combustion mode is switched from the stratified combustion mode to the homogeneous combustion mode, the combustion mode switching flag is switched to ON, and the air system control parameters (throttle opening, EGR except intake / exhaust VCT are set.
Only the valve 34 and the air flow control valve 31) are immediately switched to the target value of the stratified combustion mode which is the combustion mode of the switching destination.
As a result, the actual air-fuel ratio A / F becomes the stratified combustion region determination value CA.
When it changes to F1, set the combustion mode switching flag to OF.
By switching to F, the fuel injection mode is switched to the compression stroke injection and the actual combustion mode is switched to the stratified combustion mode.

In this embodiment, when the combustion mode is switched by the combustion mode switching request for a short time, the intake VCT
Since the exhaust VCT is fixed, the number of control parameters that need to be switched becomes smaller than in the conventional case. As a result, the time B from the generation of a short-time combustion mode switching request to the switching of the actual combustion mode to the homogeneous combustion mode becomes shorter than before, and the combustion mode switching speed can be increased. Moreover, it is possible to reduce the number of control parameter adaptation steps in the vehicle development and design stage, and to shorten the vehicle development and design period.

Further, in the present embodiment, when the combustion mode is switched by a short-time combustion mode switching request, the control parameters to be fixed are the intake VCT and the exhaust VCT, so compared with the case where other control parameters are fixed. And there are the following advantages. Since the intake VCT and the exhaust VCT are controlled by hydraulic pressure, they are control parameters having large variations in responsiveness as compared with other control parameters. Therefore, if the combustion mode is switched in a short time, the intake VC
Whether T and the exhaust VCT are fixed or switched, the influence on the air system is not so different. Therefore, a specific control parameter fixed at the time of switching the combustion mode is an intake VCT and an exhaust VC which are control parameters with large variations in response.
If T is set, the influence of fixing the control parameter can be reduced.

That is, since the intake VCT and the exhaust VCT controlled by hydraulic pressure vary in viscosity (fluidity) of the hydraulic oil depending on the oil temperature and the hydraulic pressure varies, the hydraulic pressure also varies depending on the engine rotation speed. The control accuracy is poor compared to the control parameters of. Therefore, if the combustion mode is switched in a short time, even if the intake VCT and the exhaust VCT are fixed, there is little influence, and depending on the engine operating state, it is better to fix the intake VCT and the exhaust VCT for combustion stability. It may be easy to maintain. However, the control parameter fixed at the time of switching the combustion mode is not limited to the intake VCT and the exhaust VCT, and the EGR valve may be fixed, for example.

Further, the present invention may be applied to an internal combustion engine equipped with a variable valve lift mechanism for varying the valve lift amount of intake air and / or exhaust gas. In this case, the control parameter fixed at the time of switching the combustion mode. Is a valve lift amount of intake and / or exhaust. Similarly, the present invention may be applied to an internal combustion engine equipped with a variable valve mechanism that changes both the valve timing and the valve lift amount. In this case, the control parameter fixed when switching the combustion mode is set to the valve timing. Both the valve lift amount and the valve lift amount are good.

The drive source for changing the valve timing and the valve lift amount is not limited to the hydraulic pressure, and the present invention can be applied to an internal combustion engine in which the valve timing and the valve lift amount are changed by an electromagnetic actuator or the like.

Further, in this embodiment, when the combustion mode is switched, the intake VCT and the exhaust VCT are fixed to the target values of the combustion mode before the switching, but the intake VCT and the exhaust VCT are fixed.
If CT is fixed to the target value of the combustion mode before switching,
When it is feared that the combustion stability deteriorates, the intake VCT and the exhaust VCT may be fixed to the target values for switching the combustion modes. By doing so, there is an advantage that it is possible to ensure the combustion stability during the combustion mode switching control.

Further, in this embodiment, only when the combustion mode is switched by the short-time combustion mode switching request,
When the VCT fixed combustion mode switching control is executed and the engine operating state (requested torque, engine speed, etc.) changes and a combustion mode switching request is generated during engine operation, VCT fixed combustion mode switching control is not performed, Although all the control parameters of the air system including the intake / exhaust VCT are immediately switched to the target value of the combustion mode of the switching destination, the combustion mode switching request is made due to changes in the engine operating state (requested torque, engine rotation speed, etc.). Even when occurs, the VCT fixed combustion mode switching control may be executed. In this case, after the actual combustion mode is switched to the switching destination combustion mode, the intake / exhaust VCT that has been fixed until then may be switched to the target value of the switching destination combustion mode.

The present invention is not limited to in-cylinder injection engines, and even intake port injection engines can be applied and implemented as long as the engine has a function of switching the combustion mode like a lean burn engine. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an entire engine control system according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a processing flow of an engine control main routine.

FIG. 3 is a flowchart showing a processing flow of a combustion mode determination routine.

FIG. 4 is a flowchart showing a processing flow of a combustion mode switching control routine.

FIG. 5 is a flowchart showing a flow of processing of an air system control routine.

FIG. 6 is a flowchart showing the flow of processing of a fuel system control routine.

FIG. 7 is a flowchart showing a processing flow of an ignition system control routine.

8A is a diagram showing a stable combustion region of stratified combustion and homogeneous combustion when the EGR valve is opened, and FIG. 8B shows that the stable combustion region of stratified combustion and homogeneous combustion is expanded when the EGR valve is closed. Schematic diagram

9A is a diagram showing intake / exhaust valve timing in a stratified combustion mode and VCT fixed combustion mode switching control, and FIG. 9B is a diagram showing intake / exhaust valve timing in a normal homogeneous combustion mode.

FIG. 10 is a time chart showing an example of combustion mode switching control when there is a short-time combustion mode switching request (request for NOx purging of a NOx catalyst, etc.) in a conventional cylinder injection engine.

FIG. 11 is a time chart showing an example of combustion mode switching control when there is a short-time combustion mode switching request in the embodiment of the present invention.

[Explanation of symbols]

11 ... Engine (internal combustion engine), 12 ... Intake pipe, 16 ... Throttle valve, 21 ... Fuel injection valve, 22 ... Spark plug, 25 ... Exhaust pipe, 27 ... NOx catalyst, 30 ... ECU
(Control means), 31 ... Air flow control valve, 34 ... EGR valve (exhaust gas recirculation control means), 37 ... Intake valve, 38 ... Exhaust valve, 39 ... Intake variable valve timing mechanism (intake valve changing means), 40 ... Exhaust variable Valve timing mechanism (exhaust valve variable means).

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 3G092 AA01 AA06 AA09 AA11 AA17                       AB02 BA07 BB01 DA03 DE03S                       EA06 EA07 EA11 FA04 GA14                       HA13X HB01X                 3G301 HA01 HA04 HA13 HA16 HA19                       JA04 JA23 KA06 LB04 MA01                       MA11 ND02 NE14 NE15 NE16                       PA18Z

Claims (9)

[Claims] 1. An internal combustion engine control device for controlling respective control parameters of an air system, a fuel system and an ignition system so as to switch a combustion mode between a stratified combustion mode and a homogeneous combustion mode in response to a combustion mode switching request, When a combustion mode switching request is made, at least one control parameter other than the throttle opening of the air system (hereinafter referred to as "specific control parameter") is fixed to switch the combustion mode. An internal combustion engine control device comprising control means for executing control. 2. The air system includes an intake valve varying means for varying intake valve timing and / or an intake valve lift amount, an exhaust valve varying means for varying exhaust valve timing and / or an exhaust valve lift amount, and an exhaust gas recirculation amount. The internal combustion engine control device according to claim 1, further comprising at least one of an exhaust gas recirculation control unit for controlling and an air flow control unit for controlling an air flow in the cylinder. 3. The internal combustion engine control according to claim 1, wherein the control means executes the specific control parameter fixed combustion mode switching control when the combustion mode is temporarily switched for a short time. apparatus. 4. The internal combustion engine control device according to claim 1, wherein the specific control parameter is a control parameter having a large variation in responsiveness as compared with other control parameters. . 5. The internal combustion engine control device according to claim 4, wherein the control parameter having a large variation in responsiveness is a valve timing and / or a valve lift amount on the intake side and / or the exhaust side. 6. The control means fixes the specific control parameter until the combustion mode is returned to the original combustion mode after the specific control parameter fixed combustion mode switching control is started. The internal combustion engine controller according to any one of 1 to 5. 7. The control means fixes the specific control parameter to a target value of a combustion mode immediately before that when starting the specific control parameter fixed combustion mode switching control. 7. The internal combustion engine control device according to any one of 1 to 6. 8. The control means fixes the specific control parameter to a target value for combustion mode switching when starting the specific control parameter fixed combustion mode switching control. 6. The internal combustion engine controller according to any one of 6 above. 9. In an in-cylinder injection type internal combustion engine in which fuel is directly injected into a cylinder, the control means is required to ensure NOx purging of a NOx catalyst or securing negative pressure in a brake booster during stratified charge combustion operation. The internal combustion engine controller according to any one of claims 1 to 8, wherein the specific control parameter fixed combustion mode switching control is sometimes executed.