JP2000282916A - Control device for direct injection engine of spark ignition type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure combusitibility at change-over from the stratified combustion mode to the uniform combustion mode, to promote NOx release from a NOx catalyst and the reduction, while preventing abrupt change of the torque and to enhance the catalyst refreshing effect. SOLUTION: A spark ignition type direct injection engine is furnished with a NOx catalyst and arranged, so that the degree of throttle opening is lessened at change-over from the stratified combustion mode with the compression stroke injection to the uniform combustion mode with the suction stroke injection. The arrangement further includes a delaying means 63 for delaying the switching into the suction stroke injection at mode change-over from stratified mode into uniform mode and a control means 65 for the mode change-over time. The control means 65 allows execution of the compression stroke injection and suction stroke injection during the delay period by the delaying means 63, and increases the air-fuel ratio with the compression stroke injection greater than the theoretical air-fuel ratio, while controlling the air-fuel ratio of the exhaust gas of the two types of injection lower than the theoretical air-fuel ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises an injector for directly injecting fuel into a combustion chamber, and stores NOx in an oxygen-excess atmosphere to reduce NOx as the oxygen concentration decreases.
The present invention relates to a control device for a spark ignition type direct injection engine having a NOx catalyst for releasing x in an exhaust passage of the engine.

[0002]

2. Description of the Related Art Conventionally, a spark-ignition type direct injection engine provided with an injector for directly injecting fuel into a combustion chamber and performing a lean operation by stratified combustion in order to improve fuel efficiency in a low load region has been used in an oxygen-rich atmosphere. An NOx catalyst that stores NOx and releases NOx as the oxygen concentration decreases is provided in the exhaust passage, and the NOx catalyst is used to purify NOx even during lean operation. Such N
When an Ox catalyst is provided, the NOx catalyst
It is necessary to release Ox to refresh the NOx catalyst and to reduce the released NOx. To refresh the catalyst and reduce the released NOx, the air-fuel ratio of the exhaust gas is made rich and the exhaust gas as a reducing material is reduced. CO, HC
Is required to be increased.

[0003] While lean operation by stratified combustion is performed in the stratified combustion region on the low load side, uniform combustion is performed by injecting fuel in the intake stroke while keeping the air-fuel ratio below the stoichiometric air-fuel ratio in the higher load uniform combustion region. In the engine to be performed, the NOx catalyst is refreshed by enriching the air-fuel ratio at least at the time of acceleration when shifting from the stratified combustion region to the uniform region. Further, when the lean operation in the stratified combustion mode is continued and the NOx storage amount of the NOx catalyst increases to a predetermined value or more, the air-fuel ratio is enriched below the stoichiometric air-fuel ratio for a predetermined time even in the stratified combustion region, and NOx is reduced. There is also known a catalyst designed to refresh the catalyst.

[0004]

By the way, when switching from the stratified combustion combustion mode to the uniform combustion mode, for example, at the time of acceleration when shifting from the stratified combustion region to the uniform combustion region,
For the purpose of torque adjustment, the air-fuel ratio is made rich by reducing the throttle opening at the time of mode switching and reducing the intake charge, but at this time, control to reduce the throttle opening is performed. There is a considerable delay until the intake air charge is actually reduced, and during this delay period, the intake air charge is in a state larger than an appropriate value in the uniform combustion mode. In this state, when the fuel injection is switched to the intake stroke injection and the fuel injection amount is increased to enrich the air-fuel ratio, a sudden change in torque occurs.

For this reason, the fuel injection is controlled by maintaining the state of the compression stroke injection at the lean air-fuel ratio during the delay period, and after the delay period elapses and the intake air charge is sufficiently reduced, the fuel injection control is stopped. By switching to a state in which the intake stroke injection is performed at an air-fuel ratio or lower, a sudden change in torque is prevented. However, from the viewpoint of refreshing the NOx catalyst, simply controlling the air-fuel ratio to be enriched after the intake air charge is reduced,
NOx is released from the NOx catalyst, and the released NO
The effect of reducing x is not always sufficiently obtained.

Therefore, by utilizing the above-mentioned delay period, NOx
If the air-fuel ratio of the exhaust gas is enriched in a state where the amount of exhaust gas guided to the catalyst is large, a large amount of CO and HC can be supplied to the NOx catalyst, and it is expected that the catalyst refresh and the reduction of NOx are promoted.

As a technique for promoting the refresh of the catalyst, for example, as disclosed in Japanese Patent Application Laid-Open No. 10-274085, the NOx storage amount of the NOx catalyst is equal to or more than a predetermined value and the air-fuel ratio is in a lean operating state. In some cases, in addition to the main injection for stratified combustion, additional fuel is injected during the expansion stroke to generate CO. Further, as disclosed in JP-A-4-231645, HC is supplied to the catalyst by performing a small amount of sub-injection in addition to the main injection, and the sub-injection is performed in accordance with the temperature of the NOx catalyst. There are things that change the timing.

However, in any of these prior arts, the idea of refreshing the catalyst by utilizing the delay period of the change in the intake air charge with respect to the change in the throttle opening when switching from the stratified combustion mode to the uniform combustion mode is not seen. I can't.

In view of the above circumstances, the present invention effectively utilizes the delay period of the change in the intake air charge when switching from the stratified combustion mode to the uniform combustion mode to ensure flammability and prevent a sudden change in torque. It is another object of the present invention to provide a control device for a spark ignition type direct injection engine that can enhance the effect of promoting the release of NOx from the NOx catalyst and the reduction of the released NOx.

[0010]

According to the present invention, an exhaust passage of an engine is provided with a NOx catalyst that stores NOx in an oxygen-excess atmosphere and releases NOx as the oxygen concentration decreases, and a fuel is directly injected into a combustion chamber. Combustion into a stratified combustion mode in which fuel is injected in the compression stroke while increasing the air-fuel ratio above the stoichiometric air-fuel ratio, and a uniform combustion mode in which fuel is injected in the intake stroke while keeping the air-fuel ratio below the stoichiometric air-fuel ratio. A spark-ignition direct-injection engine whose state can be changed and whose air-fuel ratio is adjusted by controlling the intake air amount adjusting means so as to reduce the intake charge amount when switching from the stratified combustion mode to the uniform combustion mode. At the time of switching from the stratified combustion mode to the uniform combustion mode, the actual A delay means for delaying the timing of switching the fuel injection from the injector to the intake stroke injection only for a time until the intake charge decreases to an appropriate value in the uniform combustion mode. In addition to fuel injection during the stroke, fuel injection during the expansion stroke is performed, and the air-fuel ratio in the combustion chamber due to the compression stroke injection is made larger than the stoichiometric air-fuel ratio. A mode switching control means for controlling the air-fuel ratio to be equal to or lower than the stoichiometric air-fuel ratio is provided (claim 1).

According to this device, when switching from the stratified combustion mode to the uniform combustion mode, the actual intake air charge is larger than the appropriate value in the uniform combustion mode due to the delay of the intake system with respect to the control of the intake air amount adjusting means. During the period in
The compression stroke injection and the expansion stroke injection are performed, and the air-fuel ratio in the combustion chamber due to the compression stroke injection is made lean, so that the combustibility due to stratified combustion is secured and a sudden increase in torque is prevented. Moreover, as described above, when the intake air charge is increased due to the delay of the intake system at the time of switching to the uniform combustion mode, the air-fuel ratio of the exhaust gas is made rich in the compression stroke injection and the expansion stroke injection. Exhaust gas with a rich air-fuel ratio is supplied to the NOx catalyst in a large amount, and NOx release and reduction are promoted.

In the present invention, the air-fuel ratio in the uniform combustion mode is set to the stoichiometric air-fuel ratio, and the air-fuel ratio of the exhaust gas is set to a value smaller than the stoichiometric air-fuel ratio in the control by the mode switching control means during the delay period due to the delay. (Claim 2) is preferred.

In this way, during the delay period, the amount of CO and HC in the exhaust gas increases, and the release of NOx from the NOx catalyst and the reduction of the released NOx are promoted. Emission is suppressed.

In the present invention, the stratified combustion mode is executed in a predetermined low load region as a stratified combustion region, and the operation region on a higher load side is defined as a uniform combustion region. The mode may be executed, and the delay by the delay unit and the control by the mode switching control unit may be performed at the time of acceleration from the stratified combustion region to the uniform combustion region (claim 3).

In this manner, during acceleration from the stratified charge combustion region, the intake air charge is controlled so as to gradually increase with an increase in the target load until the shift to the uniform combustion region,
Even after shifting to the uniform combustion region and controlling the intake air amount adjusting means in the direction of decreasing the intake air amount, the actual intake air amount tends to increase to a certain extent due to the delay of the intake system. The compression stroke injection and the expansion stroke injection are performed by the control means at the time of the mode switching during the period in which the amount of gas increases, so that the air-fuel ratio of the exhaust gas sent to the NOx catalyst is made rich and the amount of the exhaust gas is sufficiently increased, The effect of promoting NOx release and reduction is enhanced.

Alternatively, when the NOx storage amount of the NOx catalyst increases to a predetermined value or more during the operation in the stratified combustion mode, uniform combustion is performed for a predetermined time to refresh the catalyst for releasing NOx from the NOx catalyst. In addition to performing the control for changing to the mode, the delay by the delay unit and the control by the mode switching control unit may be performed when the mode is switched from the stratified combustion mode to the uniform combustion mode for the catalyst refresh (claim). Item 4).

In this way, when the mode is changed to the uniform combustion mode for catalyst refreshment during the operation in the stratified charge combustion mode, the intake air amount adjusting means is controlled in the direction of decreasing the intake air amount while the actual intake air amount is controlled. During the period in which the decrease in the amount is delayed, the compression stroke injection and the expansion stroke injection are performed by the mode switching control means, and after the intake charge is reduced, uniform combustion by the intake stroke injection at a stoichiometric air-fuel ratio or less is performed. As a result, the release of NOx from the NOx catalyst and the reduction of the released NOx (hereinafter referred to as catalyst refresh including the reduction of NOx) are promoted while ensuring the flammability and adjusting the torque in a favorable manner. You.

In the third aspect of the present invention, the control by the mode switching control means includes, for example, gradually increasing the compression stroke injection amount until the middle of the delay period by the delay means, and starting the compression stroke injection from the middle of the delay period. The amount may be gradually reduced (claim 5).

In this manner, the compression stroke injection amount is gradually increased until the middle of the delay period, so that the torque is gradually increased to match the increase in the target load due to acceleration. By suppressing the increase in the stroke injection amount, over-rich around the spark plug and an increase in the NOx generation amount can be avoided.

Further, in the invention of claim 3 or 4,
The control by the control means at the time of mode switching includes:
During the delay period by the delay means, the compression stroke injection amount is reduced from a value corresponding to the required torque, and the expansion stroke injection amount is controlled so that the required torque is obtained by the compression stroke injection and the expansion stroke injection. (Claim 6).

That is, if the expansion stroke injection is performed at a time close to the compression top dead center, the expansion stroke injection also contributes to the torque generation to some extent. Therefore, the torque generation contribution of the expansion stroke injection is expected. If the compression stroke injection amount is reduced and the expansion stroke injection amount is adjusted so that a torque (required torque) corresponding to the target load can be obtained by the compression stroke injection and the expansion stroke injection, torque adjustment and catalyst refreshing can be performed. Well done.

Further, the control means at the time of mode switching may be adapted to retard the ignition timing in addition to controlling the fuel injection during the delay period by the delay means. Alternatively, the control means at the time of mode switching controls the EGR device for recirculating a part of the exhaust gas to the intake system in a state of recirculating the exhaust gas in addition to the control of the fuel injection during the delay period by the delay means. (Claim 8). By doing so, the NOx in the exhaust gas is reduced by the ignition timing retard or the recirculation of the exhaust gas, and the CO amount and the HC amount with respect to the NOx amount are reduced.
The ratio of the amount increases, which is advantageous for improving the catalyst refresh performance.

The configuration of the engine control system in which the device of the present invention is incorporated is such that a target load is set based on the accelerator opening, and a target air-fuel ratio for controlling the intake air amount is determined based on the target load and the engine speed. An intake air amount control means for controlling the intake air amount adjusting means according to the target air-fuel ratio, and a target air-fuel ratio for injection amount control based on a value obtained by smoothing the target load and a detected value of the charging efficiency. And a fuel injection amount control means for calculating a fuel injection amount from the injector based on the target air-fuel ratio (claim 9).

By doing so, the timing of the control of the intake air amount having a low response speed and the control of the fuel injection amount having a high response speed is effectively adjusted, thereby preventing the torque shock and the emission from deteriorating. Then, based on such control, the mode switching time control means is performed during a period in which a response delay of a change in the intake air charge occurs at the time of switching from the stratified combustion mode to the uniform combustion mode, The torque adjustment is properly performed, and the refresh of the catalyst is promoted.

[0025]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 schematically shows the overall structure of a direct injection engine to which the present invention is applied. In this figure, an engine body 10 has a plurality of cylinders 12,
Each cylinder 12 has a combustion chamber 15 formed above a piston 14 inserted into its cylinder bore. The combustion chamber 15 has an intake port and an exhaust port, which are connected to an intake valve 17 and an exhaust valve. Each is opened and closed by a valve 18.

At the center of the combustion chamber 15 is a spark plug 2
0 is disposed, and the plug tip faces the combustion chamber 15. Further, the injector 2 is inserted into the combustion chamber 15 from the side.
2 comes to the front, and the injector 22
5 is directly injected with fuel. A fuel circuit having a high-pressure fuel pump, a pressure regulator, and the like (not shown) is connected to the injector 22. Fuel is supplied to the injector 22 of each cylinder and the fuel pressure is higher than a predetermined pressure in the compression stroke. The fuel circuit is configured such that

An intake passage 24 and an exhaust passage 31 are connected to the engine body 10. In the intake passage 24, an air cleaner 25, an air flow sensor 26, a throttle valve 28 and a surge tank 29 driven by a motor 27 are provided in this order from the upstream side, and the throttle valve 28 and a motor 27 Constitutes the intake air amount adjusting means.

The exhaust passage 31 is provided with a NOx catalyst 33 for purifying exhaust gas. This NOx
The catalyst 33 has NOx purification performance even in a lean operation state in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. The catalyst 33 stores NOx in the exhaust gas in an oxygen-excess atmosphere, and the air-fuel ratio changes to a rich side. When the oxygen concentration decreases, the stored NOx is released and the C present in the atmosphere is released.
NOx is reduced by a reducing material such as O.

More specifically, the NOx catalyst 3
Reference numeral 3 shows a NOx occluding material layer and a catalyst material layer formed on a carrier made of a cordierite honeycomb structure or the like in a layered manner with the former being lower (inside) and the latter being upper (outer). The NOx occluding material layer is mainly composed of activated alumina having a large specific surface area and carrying a Pt component and a Ba component as a NOx occluding material. Also,
The catalyst material layer is mainly composed of a catalyst material obtained by supporting a Pt component and a Rh component on zeolite as a supporting base material. Note that a ceria layer may be formed on the catalyst material layer.

Further, between the exhaust passage 31 and the intake passage 24, there is provided an EGR device for recirculating a part of the exhaust gas to the intake system. This EGR device connects the exhaust passage 31 and the intake passage 24. The EGR passage 35 and the EGR passage 3
5 and an EGR valve 36 interposed therebetween. The above EG
The R valve 36 is driven by an actuator to open and close.

In addition to the air flow sensor 26, the engine has a boost sensor 40 for detecting a negative pressure of intake air in the surge tank 29, a throttle opening sensor 41 for detecting a throttle opening, and a rotation speed for detecting an engine rotation speed. A sensor 42, an accelerator opening sensor 43 for detecting an accelerator opening (accelerator operation amount), an intake air temperature sensor 44 for detecting an intake air temperature, an atmospheric pressure sensor 45 for detecting an atmospheric pressure, a water temperature sensor 46 for detecting an engine cooling water temperature, Sensors such as an O2 sensor 47 for detecting the air-fuel ratio by detecting the oxygen concentration in the exhaust gas are provided, and output signals (detection signals) of these sensors are input to an ECU (control unit) 50.

The ECU 50 controls the amount and timing of fuel injection from the injector 22 and
The control of the throttle valve 28 is performed by outputting a control signal to a motor 27 that drives the throttle valve 28, the ignition timing is controlled by outputting a control signal to the ignition circuit 21, and the control of the EGR valve 36 is further performed. Also do it.

As the basic control of the direct injection engine of the present embodiment, a predetermined low load region is a stratified combustion region, and a region on the higher load side is a uniform combustion region. In the stratified combustion region, fuel is injected from the injector 22 at a later stage of the compression stroke, so that a stratified combustion mode is set such that combustion is performed in a stratified state in which the air-fuel mixture is unevenly distributed near the ignition plug 20. In this case, the air-fuel ratio of the entire combustion chamber is set to a large lean state (for example, 30 or more) by increasing the opening degree of the throttle valve 28 and increasing the intake air amount. On the other hand, in the uniform combustion region, fuel injection is started from the injector 22 in the first half of the intake stroke while the air-fuel ratio is equal to or lower than the stoichiometric air-fuel ratio (the excess air ratio λ is λ ≦ 1). The combustion mode is a uniform combustion mode in which combustion is performed in a state where the air-fuel mixture is uniformly diffused.

FIG. 2 shows the structure of the means functionally included in the ECU 50. The ECU 50 has an intake density state detecting means 51 for detecting an intake density state based on signals from the intake air temperature sensor 44 and the atmospheric pressure sensor 45, and outputs signals from the accelerator opening sensor 43 and the engine speed sensor 42. A target load setting means 52 for setting a value corresponding to the target load based on the intake air density state based on the intake air density state.

The target load setting means 52 determines a standard operating condition for keeping the air-fuel ratio at the stoichiometric air-fuel ratio from the virtual volume efficiency obtained from the map according to the accelerator opening accel and the engine speed ne and the intake air density state. A charging efficiency corresponding to the required engine torque in the assumed case is obtained as a virtual charging efficiency, and a target indicated average effective pressure which is a value corresponding to the virtual charging efficiency is obtained from the virtual charging efficiency, and this is set as a target load.

In this case, while the first target indicated mean effective pressure Piobj is obtained by a predetermined calculation, the virtual filling efficiency is smoothed, and the second target indicated mean is calculated from the virtual filling efficiency after the smoothing process. The effective pressure Piobjd is obtained.

The ECU 50 further includes an operation mode setting means 5
The operation mode setting means 53 sets a basic operation mode mods according to the first target indicated mean effective pressure Piobj and the engine speed ne. That is, as shown in FIG. 3, in a region where the first target indicated mean effective pressure Piobj is lower than the set value and the engine speed ne is lower than the set speed (stratified combustion region), the stratified combustion mode is set. In the higher load side and higher rotation side regions (uniform combustion region), the uniform combustion mode (stoichiometric mode) with λ = 1
And In the uniform combustion region, the air-fuel ratio may be set to be richer than the stoichiometric air-fuel ratio (λ <1) in the full-open region of the accelerator and in the high-load region and the high-speed region around the accelerator region.

Further, the ECU 50 controls the amount of intake air adjusted by the throttle valve 28, the amount of fuel injected from the injector 22 and the fuel injection timing, and the EGR adjusted by the EGR valve 36.
The values of various control parameters such as the amount and the ignition timing of the spark plug 20 are determined according to the target load, the engine speed ne, and the like. In this case, the control parameters for controlling the control parameter having a low response speed (low-speed response system) such as the intake air amount and the control of the control parameter having a high response speed (high-speed response system) such as the fuel injection amount are adjusted. Among them, the first target indicated mean effective pressure Piobj is used as the target load for determining the control value of the low-speed response system, and the second target is used as the target load for determining the control value of the high-speed response system. The indicated mean effective pressure Piobjd is used.

That is, among the above control parameters, the intake air amount and the EGR amount are determined by the throttle valve 28 and E
This is a low-speed response system having relatively low responsiveness to the operation of the GR valve, and the control amounts of the throttle opening tvoobj and the control amount of the EGR valve 36 are the first target indicated average effective pressure.
It is determined according to Piobj and the engine speed ne. On the other hand, the fuel injection amount, the fuel injection timing, and the ignition timing are a high-speed response system that quickly responds to the control signal, and the fuel injection amount, the fuel injection timing, and the ignition timing are the second target indicated average effective pressure Piobjd and the engine. It is determined according to the rotation speed ne and the like.

More specifically, as means for controlling the intake air amount, a target air-fuel ratio setting means 54 and a throttle opening degree calculating means 55 are provided. The target air-fuel ratio setting means 54 sets the target air-fuel ratio afwb for controlling the intake air amount for each operation mode mods set by the operation mode setting means 53. In the stratified combustion mode, the first target indicated average According to the effective pressure Piobj and the engine speed ne, a target air-fuel ratio afwb is obtained from a map created in advance, and
In the stoichiometric mode, the target air-fuel ratio afwb is set to the stoichiometric air-fuel ratio.

The throttle opening calculating means 55 calculates a target charging efficiency from a virtual charging efficiency (a value corresponding to a target load assuming a state of operation at a stoichiometric air-fuel ratio) corresponding to the target load and the target air-fuel ratio afwb. Is calculated from the target charging efficiency taking into account the intake air density correction, and the throttle opening is determined according to the target volume efficiency and the engine speed ne.

The means for controlling the fuel injection from the injector 22 includes a target air-fuel ratio creating means 56, an injection amount calculating means 57, an injection timing setting means 58, and an injection controlling means 59.
Having.

The target air-fuel ratio creating means 56 obtains a target air-fuel ratio for controlling the fuel injection amount and the like, and obtains a target air-fuel ratio afw0 in a transient state and a target air-fuel ratio afwbd in a steady state. One of the target air-fuel ratios afw0 and afwbd is selected to determine the final target air-fuel ratio afw.

The target air-fuel ratio afw0 at the time of the transition is set so that the torque corresponding to the target load can be obtained under the actual charging efficiency.
Is calculated based on the target indicated average effective pressure Piobjd or the virtual charging efficiency and the actual charging efficiency ce corresponding to the target average effective pressure Piobjd in consideration of the fuel efficiency improvement effect. On the other hand, the steady-state target air-fuel ratio af
In the stratified charge combustion mode, wbd is obtained from a map prepared in advance according to the second target indicated mean effective pressure Piobjd and the engine speed ne, and is set to the stoichiometric air-fuel ratio (λ = 1) in the stoichiometric mode. . Then, during a transition in which the deviation dafwb between the target air-fuel ratio afwb for intake air amount control and the target air-fuel ratio afw0 becomes large, the target air-fuel ratio afw0 is set to the final target air-fuel ratio afw. The target air-fuel ratio afwbd is set as the final target air-fuel ratio afw.

The injection amount calculating means 57 calculates a basic injection amount from the actual charging efficiency ce obtained from the output of the air flow sensor 26 and the target air-fuel ratio afw obtained by the target air-fuel ratio creating means 56, and further calculates various basic injection amounts. The final injection amount is calculated taking into account the correction value, and the injection pulse width is proportional to this final injection amount.
Ask for Ti.

The injection timing setting means 58 controls the fuel injection timing th
tinj is set for each operation mode, and in the stratified combustion mode, the injection timing for the compression stroke injection is obtained from a map created in advance according to the second target indicated mean effective pressure Piobjd and the engine speed ne, In the stoichiometric mode, the injection timing for the intake stroke injection is obtained from a table created in advance according to the engine speed ne.

The injection control means 59 operates the injector 22 at the injection timing set by the injection timing setting means 58 for a time corresponding to the injection pulse width Ti calculated by the injection amount calculation means. Outputs injection pulse.

Reference numeral 60 denotes ignition timing control means.
In the stratified charge combustion mode, the second target indicated mean effective pressure Piobjd
The basic ignition timing is obtained from the map according to the engine speed ne and the engine speed ne.In the stoichiometric mode, the basic ignition timing is obtained from the map according to the actual filling amount, ce and the engine speed ne. The ignition timing is obtained from various correction values according to the water temperature and the like. 61 is EG
R control means for obtaining a basic EGR valve control amount from a map in accordance with the first target indicated mean effective pressure Piobj and the engine speed ne in the stratified combustion mode, and in the stoichiometric mode, the actual charge amount, ce and engine The basic EGR valve control amount is obtained from a map according to the rotational speed ne.
The EGR valve control amount is calculated by adding various correction values to the GR valve control amount, and a control signal corresponding to the EGR valve control amount is output to the EGR valve 36.

Further, in addition to the above-mentioned units, the ECU 50 is provided with a delay unit 63 and a mode switching control unit 65 in order to promote refresh of the catalyst when switching from the stratified mode to the uniform mode.

When the operation mode set by the operation mode setting means 53 is switched from the stratified combustion mode to the uniform combustion mode, the delay means 63 starts the control for reducing the throttle opening and reducing the intake air charge. The timing at which the fuel injection from the injector 22 is switched to the intake stroke injection is delayed by the time from when the fuel injection amount is reduced to the appropriate value in the uniform combustion mode.

The mode switching control means 65
Changes the control by the injection control means 59 during the delay period by the delay means 63 to cause the injector 22 to perform fuel injection in the expansion stroke in addition to fuel injection in the compression stroke. That is, as shown in FIG. 4, the fuel injection from the injector 22 is controlled by the compression stroke injection in the stratified combustion mode and the intake stroke injection in the uniform combustion mode, but is controlled when the combustion mode is switched from the stratified combustion mode to the uniform combustion mode. During the above delay period, in addition to the compression stroke injection,
The expansion stroke injection is performed. The timing of the expansion stroke injection may be set, for example, in the first half of the expansion stroke close to the compression top dead center.

When the compression stroke injection and the expansion stroke injection are performed during the delay period, the compression stroke injection and the expansion stroke injection are performed while the air-fuel ratio in the combustion chamber due to the compression stroke injection is made larger than the stoichiometric air-fuel ratio. The respective injection amounts are controlled so that the air-fuel ratio of the exhaust gas becomes equal to or less than the stoichiometric air-fuel ratio.

The mode switching control means 6
5 changes the ignition timing control by the ignition timing control means 60 in addition to the above-described fuel injection control during the delay period by the delay means 63 so that the ignition timing is retarded, or Via valve control means 61,
The EGR valve 36 may be controlled so as to increase the EGR amount as compared to when in the uniform combustion mode.

FIG. 5 is a flowchart showing a process mainly performing the functions of the delay means 63 and the mode switching control means 65.

When the process of this flowchart starts, first, in step S1, various signals such as the engine speed, the accelerator opening, the air flow sensor output, and the water temperature are input. Next, in step S2, the target load and the engine speed are determined. The operation mode mods set by the operation mode setting means 53 is checked based on the result, and it is determined whether or not the operation mode is the stratified combustion mode. If it is determined that the mode is the stratified combustion mode, the compression stroke injection is performed in step S3.

If it is determined in step S2 that the mode is not the stratified combustion mode (it is the uniform combustion mode), it is determined in step S4 whether the previous mode was also the uniform combustion mode.

When the determination in step S4 is NO, that is, when the mode is switched from the stratified combustion mode to the uniform combustion mode, a timer is set in step S5, and
In step S6, compression stroke injection and expansion stroke injection are performed. The time set by the timer is set to a value corresponding to the time required from the switching of the operation mode set by the operation mode setting means until the intake air charge decreases to an appropriate value in the uniform combustion mode. Since the time required for the intake air charge to decrease to the appropriate value in the uniform combustion mode from the point of time when the operation mode is switched varies depending on the engine speed, the above time at various engine speeds is experimentally examined in advance, and the table is used. In the step S5, it is desirable that a time corresponding to the engine speed at that time is obtained from the table and set in the timer.

If the determination in step S4 is YES, it is determined in step S7 whether or not the timer is set to 0, and the elapsed time from the time of switching to the uniform combustion mode is set by the timer. It is checked whether it is within the time. If the elapsed time from the switching time is within the set time, step S6
The state where the compression stroke injection and the expansion stroke injection are performed is maintained.

When the determination in step S7 is NO,
That is, when the elapsed time from the switching point exceeds the set time, in step S8, the intake stroke injection is performed as normal control in the uniform combustion mode.

The operation of the apparatus according to the present embodiment will be described more specifically with reference to the time chart of FIG.

In the low load side stratified combustion region where the accelerator opening is small and the charging efficiency is low, the air-fuel ratio (A / F) is significantly lean, and fuel is injected from the injector 22 in the compression stroke. Thus, a stratified combustion state that is advantageous for improving fuel efficiency is obtained. During the lean operation by the stratified combustion, NOx in the exhaust gas is stored in the NOx catalyst 33.

When an acceleration operation is performed by depressing the accelerator pedal from this state, as shown in FIG. 6, while in the stratified combustion region, the throttle operation is started in response to the increase in the accelerator opening from the acceleration operation start time t0. As the opening gradually increases, the filling efficiency gradually increases. When the target load (first target indicated mean effective pressure Piobj) that increases in accordance with the accelerator opening exceeds a predetermined value and shifts to the uniform combustion region, the throttle opening is performed at time t1 to enrich the air-fuel ratio. However, the charging efficiency ce increases to some extent even after the throttle opening decreases, and then gradually decreases until the charging efficiency ce
There is a considerable lag time before is close enough to the steady state value in homogeneous combustion mode.

Therefore, the time T2 from the time point t1 when the throttle opening is reduced to the time point t2 when the charging efficiency decreases within a proper range in the uniform combustion mode (within a predetermined range from a steady state value in the uniform combustion mode). Switching to the intake stroke injection for achieving a uniform combustion state is delayed by (the time set by the timer in step S5 in FIG. 5).

During the delay period T, the fuel injection from the injector 22 is controlled so that the compression stroke injection and the expansion stroke injection are performed. In this case, the air-fuel ratio in the combustion chamber due to the compression stroke injection is leaner than the stoichiometric air-fuel ratio (A / F = 14.7) as shown by a broken line a in FIG. The air-fuel ratio of the exhaust gas due to both the expansion stroke injection and the exhaust air-fuel ratio is made rich below the stoichiometric air-fuel ratio as shown by the solid line b, thereby ensuring flammability and preventing a sudden change in torque.
The catalyst refresh effect of releasing and reducing the catalyst is enhanced.

That is, in order to enhance the catalyst refreshing effect, it is effective to enrich the air-fuel ratio of the exhaust gas to increase CO and HC as a reducing agent in the exhaust gas. If it becomes, the surroundings of the spark plug become over-rich and the combustibility deteriorates.
If the air-fuel ratio is enriched by switching to the uniform combustion state by the intake stroke injection, the combustibility is ensured, but due to the primary delay of the intake system, the intake charge is excessive compared to the appropriate value in the uniform combustion mode. In order to enrich the air-fuel ratio in this way during the above-mentioned delay period T, it is necessary to increase the amount of fuel injection, which causes a sudden increase in torque.

On the other hand, in the device of the present invention, during the delay period T, the stratified charge combustion is performed at the lean air-fuel ratio by the compression stroke injection, so that the combustibility is secured even in the excessive intake state and the torque is reduced. A rapid increase is avoided, and the air-fuel ratio of the exhaust gas is made rich by performing the expansion stroke injection in addition to the compression stroke injection, thereby promoting the refreshing of the NOx catalyst. Particularly, since the air-fuel ratio of the exhaust gas is made rich during the delay period in which the charging efficiency is high due to the primary delay of the intake system, the uniform combustion mode after the charging efficiency has decreased (after the delay period T has elapsed). As compared with the case where the air-fuel ratio is made richer, the amount of exhaust gas with a rich air-fuel ratio becomes larger, so that CO and HC supplied to the NOx catalyst 33 are increased.
Is increased, and the NOx release and reduction actions are enhanced.

Further, in the apparatus of the present embodiment, the target air-fuel ratio afwb for controlling the intake air amount set based on the first target indicated mean effective pressure Piobj corresponding to the target load and the engine speed ne. While the throttle opening is controlled, the control of the fuel injection amount during the transition is controlled by the second target indicated mean effective pressure Pi.
The target air-fuel ratio af at the time of the transition for the injection amount control obtained based on objd (the target load subjected to the annealing process) and the charging efficiency ce.
Since the adjustment is performed according to w0, the air-fuel ratio and the torque are appropriately adjusted even during the transition, and the torque shock and the deterioration of the emission are prevented. Then, based on such control, the control of the fuel injection amount during the delay period at the time of switching from the stratified combustion mode to the uniform combustion mode can be appropriately performed.

For example, the injection amount calculated in accordance with the target air-fuel ratio afw0 at the time of transition for the injection amount control is defined as the compression stroke injection amount, and the injection necessary to obtain a predetermined rich air-fuel ratio equal to or lower than the target air-fuel ratio. An amount corresponding to the difference between the amount and the compression stroke injection amount may be set as the expansion stroke injection amount.

That is, the transient target air-fuel ratio afw0 obtained by the target air-fuel ratio creating means 56 is obtained so that a torque corresponding to the target load can be obtained under the actual charging efficiency. In a situation where the charging efficiency is higher than in the steady state, the target air-fuel ratio afw0 is made lean so that a torque corresponding to the target load is obtained. Since the compression stroke injection mainly contributes to the torque among the compression stroke injection and the expansion stroke injection, the injection amount is set according to the target air-fuel ratio afw0, and the compression stroke injection is thus performed. If the expansion stroke injection amount is set so that the air-fuel ratio of the exhaust gas is equal to or lower than the stoichiometric air-fuel ratio while setting the amount, the torque adjustment and the catalyst refresh can be performed satisfactorily.

In the control during the delay period, during the delay period, the compression stroke injection amount may be gradually increased in order to increase the torque according to the increase in the target load due to the acceleration operation. From the middle of the period, it is preferable to control so as to suppress the increase in the compression stroke injection amount in order to avoid over-rich around the spark plug and increase in the amount of NOx generated.

By performing the expansion stroke injection at a time close to the compression top dead center, the expansion stroke injection can also contribute to torque generation to some extent. In this case, the compression stroke injection amount is set to the target air-fuel ratio af in consideration of the torque generation contribution of the expansion stroke injection.
In addition to performing a reduction correction from a value corresponding to w0 (a value at which a torque corresponding to the target load is obtained under the actual filling efficiency), a torque (requested torque) corresponding to the target load is obtained by the compression stroke injection and the expansion stroke injection. May be adjusted so as to obtain the expansion stroke.

In addition, if the ignition timing is retarded in addition to the above-described fuel injection control during the delay period, the amount of NOx discharged from the combustion chamber is reduced. Ratio (CO / NOx, HC /
NOx) becomes larger, which causes the NOx catalyst 33
The effect of promoting the release and reduction of NOx from is further enhanced. Even if EGR is performed instead of or in addition to the retard of the ignition timing, the N
Due to the decrease in Ox, CO / NOx and HC / NOx increase, and the catalyst refresh effect is enhanced.

In the above embodiment, the NOx catalyst 33 is refreshed at the time of acceleration when shifting from the stratified combustion region to the uniform combustion region. However, the NOx storage amount of the NOx catalyst becomes a predetermined value during the lean operation in the stratified combustion mode. When the state becomes greater than or equal to the value, the NOx catalyst is refreshed by changing to the uniform combustion mode in which the intake stroke is injected at the stoichiometric air-fuel ratio or less for a predetermined time, and the stratified combustion in this case is performed. When the mode is switched to the uniform combustion mode, the delay by the delay unit and the control by the mode switching control unit may be performed.

That is, even when the operation is switched to the uniform combustion mode for refreshing the NOx catalyst while the operation in the stratified combustion region is continued, the control for reducing the throttle opening to enrich the air-fuel ratio is also required. In the period during which the delay occurs, the compression stroke injection and the expansion stroke injection are performed, so that the combustion is ensured and the torque fluctuation is suppressed, and the catalyst is reduced. The refresh effect is enhanced.

[0075]

As described above, according to the present invention, in the direct injection engine equipped with the NOx catalyst, when the mode is switched from the stratified combustion mode to the uniform combustion mode, after the intake air amount adjusting means is controlled in the intake air charge decreasing direction, During the delay period until the intake air charge decreases, the expansion stroke injection is performed in addition to the compression stroke injection, and the air-fuel ratio in the combustion chamber due to the compression stroke injection is made larger than the stoichiometric air-fuel ratio. Since the air-fuel ratio of the exhaust gas due to the stroke injection is set to be equal to or lower than the stoichiometric air-fuel ratio, when the mode is switched, while ensuring the flammability and performing the torque adjustment satisfactorily, the intake charge amount increases during the delay period. To supply a large amount of exhaust gas with a rich air-fuel ratio to the NOx catalyst, thereby promoting NOx release and reduction and enhancing the catalyst refreshing effect. Kill.

In particular, if the delay by the delay means and the control by the mode switching control means are performed during acceleration when shifting from the stratified combustion area on the low load side to the uniform combustion area on the high load side, uniform acceleration can be achieved by acceleration. Since the intake air charge increases due to the delay of the intake system when the engine shifts to the region, the rich air-fuel ratio exhaust gas supplied to the NOx catalyst is sufficiently increased by using this, and the catalyst refresh effect is greatly improved. Can be enhanced.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram showing an embodiment of the apparatus of the present invention.

FIG. 2 is a block diagram showing a functional configuration of an ECU.

FIG. 3 is an explanatory diagram showing an area setting of an operation mode.

FIG. 4 is an explanatory diagram showing timing of fuel injection.

FIG. 5 is a flowchart illustrating a specific example of control.

FIG. 6 is a time chart showing changes in various control parameters and the like when switching from a stratified combustion mode to a uniform combustion mode by an acceleration operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Engine main body 15 Combustion chamber 20 Spark plug 22 Injector 24 Intake passage 31 Exhaust passage 33 NOx catalyst 36 EGR valve 50 ECU 63 Delay means 65 Mode switching control means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/02 310 F02D 41/02 310E 41/14 330 41/14 330A 41/34 41/34 H 43 / 00 301 43/00 301B 301E F02P 5/15 F02P 5/15 BF (72) Inventor Takeo Yamauchi 3-1, Fuchu-cho Shinchi, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Masayuki Tetsuno Aki, Hiroshima Prefecture No.3-1 Shinchi, Gunfu-cho Mazda Co., Ltd. (72) Inventor Keiji Araki No.3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima F-term (reference) 3G022 AA00 AA07 AA10 CA00 CA04 CA09 DA02 DA06 GA05 GA06 GA07 GA08 GA09 GA11 3G084 AA00 AA04 BA09 BA13 BA15 BA17 BA20 CA03 CA04 DA10 FA01 FA02 FA07 FA10 FA11 FA20 FA29 FA33 3G092 AA01 AA06 AA09 AA17 BA04 BA09 BB02 BB06 DC08 EA02 FA06 FA17 FA18 GA05 GA06 GA12 HA01Z HA04Z HA05Z HA06Z HC01Z HD05Z HE01Z HE08Z HF08Z HG07Z 3G301 HA01 HA04 HA13 HA16 JA25 JA26 JA28 KA08 KA09 KA12 LA00 LA03 LB04 MA01 MA12 MA19 NE06 NE21 PA01Z PA07 PA07Z10

Claims (9)

[Claims] 1. An exhaust passage of an engine includes a NOx catalyst that stores NOx in an oxygen-excess atmosphere and releases NOx as the oxygen concentration decreases, and an injector that directly injects fuel into a combustion chamber is provided. The combustion state can be changed between a stratified combustion mode in which fuel is injected in the compression stroke while increasing the fuel ratio above the stoichiometric air-fuel ratio, and a uniform combustion mode in which fuel is injected in the intake stroke while the air-fuel ratio is kept below the stoichiometric air-fuel ratio, In the spark ignition type direct injection engine in which the air-fuel ratio is adjusted by controlling the intake air amount adjusting means so as to reduce the intake air charge amount when switching from the stratified combustion mode to the uniform combustion mode, At the time of switching to the combustion mode, the intake air amount adjusting means is controlled in the direction of decreasing the intake air charge amount, and then the actual intake air charge becomes uniform. And a delay means for delaying the timing of switching the fuel injection from the injector to the intake stroke injection only for a time until the fuel injection from the injector is reduced to the appropriate value in the compression stroke. In addition, the fuel is injected during the expansion stroke, and
The mode switching control means controls the air-fuel ratio in the combustion chamber by the compression stroke injection to be larger than the stoichiometric air-fuel ratio while controlling the air-fuel ratio of the exhaust gas by the compression stroke injection and the expansion stroke injection to be equal to or lower than the stoichiometric air-fuel ratio. A control device for a spark ignition type direct injection engine, comprising: 2. The method according to claim 1, wherein the air-fuel ratio in the uniform combustion mode is a stoichiometric air-fuel ratio, and the air-fuel ratio of the exhaust gas is set to a value smaller than the stoichiometric air-fuel ratio in the control by the mode switching control means during the delay period due to the delay. The control device for a spark ignition type direct injection engine according to claim 1, wherein: 3. The stratified combustion mode is executed in this region with a predetermined low load region as a stratified combustion region, and the uniform combustion mode is executed in this region with a higher load operation region as a uniform combustion region. 3. The spark-ignition direct injection engine according to claim 1, wherein a delay by said delay means and a control by said mode switching control means are performed at the time of acceleration when shifting from the stratified combustion area to the uniform combustion area. Control device. 4. During operation in the stratified combustion mode, NOx
When the NOx occlusion amount of the catalyst increases to a predetermined value or more, control is performed to change to a uniform combustion mode for a predetermined time for a catalyst refresh for releasing NOx from the NOx catalyst, and a stratification for the catalyst refresh is performed. When switching from combustion mode to uniform combustion mode,
3. The control device for a spark ignition type direct injection engine according to claim 1, wherein a delay by the delay unit and a control by the mode switching control unit are performed. 5. The control device according to claim 1, wherein said mode switching control means controls the injection amount of the compression stroke to be gradually increased until the middle of the delay period by the delay means, and to be gradually decreased from the middle of the delay period. The control device for a spark ignition type direct injection engine according to claim 3, characterized in that: 6. The mode switching control means reduces the compression stroke injection amount from a value corresponding to the required torque during the delay period by the delay means, and reduces the required torque between the compression stroke injection and the expansion stroke injection. The injection amount of the expansion stroke is controlled so as to be obtained.
A control device for a spark ignition type direct injection engine according to the above description. 7. The control method according to claim 1, wherein the mode switching control means retards ignition timing in addition to controlling fuel injection during a delay period of the delay means. Control device for spark ignition type direct injection engine. 8. The control means at the time of mode switching performs an EGR device that recirculates a part of exhaust gas to an intake system in addition to controlling fuel injection during a delay period of the delay means. The control device for a spark ignition type direct injection engine according to any one of claims 1 to 7, wherein the control is performed to a state. 9. A target load is set based on an accelerator opening, a target air-fuel ratio for intake air amount control is determined based on the target load and an engine speed, and an intake air amount adjusting means is determined according to the target air-fuel ratio. A target air-fuel ratio for injection amount control is determined based on a value obtained by smoothing the target load and a detected value of the charging efficiency, and the fuel from the injector is determined based on the target air-fuel ratio. 2. A fuel injection amount control means for calculating an injection amount.
9. The control device for a spark ignition type direct injection engine according to any one of claims 1 to 8.