JP2005220823A - Control device for cylinder injection type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve combustion stability when employing heavy fuel in a cylinder injection type engine. <P>SOLUTION: When employing heavy fuel in a high EGR range in which an external EGR quantity and a valve overlap quantity (an internal EGR quantity) are the prescribed value A or higher during the stratified combustion operation, the suction quantity of new air in a cylinder is increased to raise combustion temperature by controlling the external EGR quantity and the valve overlap quantity (the internal EGR quantity) in a reducing direction, thereby reducing smoke during employment of heavy fuel. When employing heavy fuel in a low EGR range in which the external EGR quantity and the valve overlap quantity are the prescribed value C or lower during the stratified combustion operation, the temperature in a cylinder is increased to induce atomization by controlling the external EGR quantity and the valve overlap quantity in an increasing direction, thereby reducing smoke during employment of heavy fuel. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a control device for a direct injection internal combustion engine with improved control characteristics when using heavy fuel.

  In recent years, the demand for in-cylinder injection engines (direct injection engines) that have the features of low fuel consumption, low exhaust emission, and high output has been increasing rapidly. This in-cylinder injection engine has two combustion modes, a stratified combustion mode and a homogeneous combustion mode. In the low-load region, it switches to the stratified combustion mode, and a small amount of fuel is directly injected into the cylinder in the compression stroke and ignited. A stratified mixture is formed in the vicinity of the plug and stratified combustion is performed.In the middle and high load regions, the mode is switched to the homogeneous combustion mode, the fuel injection amount is increased, and the fuel is directly injected into the cylinder in the intake stroke to perform homogeneous mixing. A gas is formed and homogeneously combusted.

  This in-cylinder injection engine includes an exhaust gas recirculation device (EGR) that circulates part of exhaust gas to the intake system, and an airflow control valve that controls the strength of airflow (swirl flow and tumble flow) generated in the cylinder. More recently, there are an increasing number of those equipped with a variable valve timing mechanism for changing the opening and closing timing of the intake valve and the exhaust valve, and various techniques for controlling these mechanisms have been proposed.

  For example, in Patent Document 1 (Japanese Patent Publication No. 6-58067), the influence of the load is eliminated by controlling the swirl control valve so as to change the swirl ratio according to the load during the stratified combustion operation. .

  Further, in Patent Document 2 (Japanese Patent Laid-Open No. 11-50853), the combustion state suddenly changes during acceleration / deceleration by controlling the swirl control valve so as to change the swirl strength according to the engine rotation speed during the stratified combustion operation. I try to prevent that.

Further, in Patent Document 3 (Japanese Patent Application Laid-Open No. 7-119513), the NOx emission amount is reduced while torque fluctuation is reduced by controlling the EGR valve opening degree according to the combustion pressure fluctuation (torque fluctuation). ing.
Japanese Patent Publication No. 6-58067 (2nd page, etc.) JP-A-11-50853 (first page, etc.) Japanese Patent Laid-Open No. 7-119513 (page 3, etc.)

  In general, the control parameters of the exhaust gas recirculation device, the airflow control valve, and the variable valve timing mechanism are adapted using a fuel having a standard fuel property (standard fuel). Therefore, the technology of each of the above patent documents is adapted to control parameters on the premise that standard fuel is used, and fuel properties are not considered at all.

  However, the fuel properties of the fuel actually used in the market are various, and the evaporation characteristics of the fuel injected from the fuel injection valve, and thus the atomization characteristics, vary depending on the fuel properties. For this reason, when heavy fuel with poor atomization characteristics is used, the injection parameters cannot be sufficiently atomized with the control parameters adapted to the standard fuel, and the combustion state deteriorates, resulting in smoke emissions. There is a problem that increases or drivability deteriorates.

  The present invention has been made in view of such circumstances. Therefore, the object of the present invention is to ensure a stable combustion state even when heavy fuel is used, and to reduce smoke and drivability when heavy fuel is used. It is an object of the present invention to provide a control device for a direct injection internal combustion engine that can achieve improvement.

  In order to achieve the above object, the invention according to claim 1 is directed to a control apparatus for a direct injection internal combustion engine in which fuel is injected into a cylinder in an intake stroke or a compression stroke to perform homogeneous combustion or stratified combustion from an exhaust system. At least one of an exhaust recirculation control means for controlling the external exhaust recirculation flow rate (external EGR amount) recirculating to the intake system and a variable valve mechanism for changing the opening / closing operation of the intake valve and / or the exhaust valve is provided. When it is determined by the property determination means and it is determined that the fuel is heavy, the exhaust recirculation control means and / or the variable valve mechanism is controlled so as to reduce the external EGR amount and / or the valve overlap amount than when the light fuel is used. It is controlled by means.

  Here, when the valve overlap amount increases, the internal EGR amount (the amount of combustion gas remaining in the cylinder) increases. As the external EGR amount and the internal EGR amount increase, the intake amount of fresh air into the cylinder decreases, and the combustion temperature decreases. For this reason, when using heavy fuels that are less atomized and combustible than light fuels, the combustion state tends to become unstable in the operating region where the external EGR amount and internal EGR amount are large, and the combustion temperature decreases. Smoke is likely to occur.

  In consideration of this characteristic, in the present invention, when it is determined that the fuel is heavy, the exhaust gas recirculation control means and / or the variable valve mechanism is set to the external EGR amount and / or the valve overlap amount (internal) than when the light fuel is used. EGR amount) is controlled to decrease. Decreasing the external EGR amount or the internal EGR amount increases the intake amount of fresh air into the cylinder and raises the combustion temperature. Therefore, when using heavy fuel, the external EGR amount and the valve overlap amount (internal EGR amount) )) Or both of them can be controlled in the direction of decreasing, so that even heavy fuel can be stably burned by the effect of increasing the amount of fresh air intake and increasing the combustion temperature. Smoke reduction and drivability improvement can be realized.

  By the way, the external EGR and the internal EGR have an action of increasing the in-cylinder temperature (intake air temperature) and promoting the atomization of the fuel. Therefore, if the external EGR amount or the internal EGR amount becomes too small, the in-cylinder temperature is increased. It becomes lower than the temperature range required to atomize heavy fuel, and when heavy fuel is used, fuel atomization is insufficient, piston wet (fuel attached to the piston) increases, and smoke is reduced. It tends to occur.

  As a countermeasure against this, when it is determined that the fuel is heavy as in claim 2, the exhaust gas recirculation control means and the exhaust gas flow control means and the valve overlap amount (internal EGR amount) are less than or equal to a predetermined value. It is preferable to control the variable valve mechanism in a direction to increase the external EGR and / or the valve overlap amount (internal EGR amount).

  In this way, when the external EGR amount and the internal EGR amount are reduced, the in-cylinder temperature becomes lower than the temperature range necessary for atomizing the heavy fuel. The in-cylinder temperature can be increased by increasing both or one of the external EGR amount and the valve overlap amount (internal EGR amount), thereby promoting the atomization of the fuel, and the piston Wet can be reduced, and smoke when using heavy fuel can be reduced.

  The control according to the fuel properties of claims 1 and 2 described above may be executed only during the stratified combustion operation, not during the homogeneous combustion operation (claim 3). Homogeneous combustion operation in which fuel is injected in the intake stroke is longer than stratified combustion operation in which fuel is injected in the compression stroke, so the time from fuel injection to ignition is longer and the fuel atomization time is longer. Inside, the time required for atomization of heavy fuel can be secured without special control according to the fuel properties, and the mixing of fuel and air can be promoted by the airflow of the intake air. Combustion stability can be ensured even with heavy fuel.

  Further, as described in claim 4, during the stratified charge combustion operation, when it is determined that the fuel is heavy fuel, the air flow control valve may be controlled in a direction in which the air flow is strengthened more than when light fuel is used. In this way, when stratified combustion operation is performed with heavy fuel, mixing of fuel and air is promoted by strengthening the airflow (swirl flow and tumble flow) generated in the cylinder, so that the fuel mist The combustion stability can be ensured even with heavy fuel.

  Hereinafter, three Examples 1 to 3 embodying the best mode for carrying out the present invention will be described.

  A first embodiment of the present invention will be described with reference to FIGS. First, a 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 the intake pipe 12 of the direct injection engine 11 that is an in-cylinder internal combustion engine, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. Is provided. A throttle valve 16 driven by a motor 15 such as a DC motor is provided on the downstream side of the air flow meter 14, and an opening degree (throttle opening degree) of the throttle valve 16 is detected by a throttle opening degree sensor 17.

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

  A fuel injection valve 21 that directly injects fuel into the 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, and the air-fuel mixture in the cylinder is ignited by the spark discharge of each spark plug 22. The intake valve 37 of the engine 11 is provided with a variable valve timing mechanism 39 (variable valve mechanism) that varies the opening / closing timing.

  A knock sensor 32 for detecting knocking and a cooling water temperature sensor 23 for detecting cooling water temperature are attached to the cylinder block of the engine 11. A crank angle sensor 24 that outputs a crank angle signal at every predetermined crank angle is attached to the outer peripheral side of the crankshaft (not shown). Based on the output signal of the crank angle sensor 24, the crank angle and the engine speed are detected.

  On the other hand, the exhaust pipe 25 of the engine 11 is provided with an upstream catalyst 26 and a downstream catalyst 27 for purifying the exhaust gas, and the air-fuel ratio or rich / lean of the exhaust gas is detected on the upstream side of the upstream catalyst 26. An exhaust gas sensor 28 (air-fuel ratio sensor, oxygen sensor, etc.) is provided. In the first embodiment, a three-way catalyst for purifying CO, HC, NOx and the like in the exhaust gas is provided near the stoichiometric air-fuel ratio as the upstream side catalyst 26, and a NOx occlusion reduction type catalyst is provided as the downstream side catalyst 27. Yes. The NOx occlusion reduction type catalyst 27 occludes NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is lean, and reduces and purifies the occluded NOx when the air-fuel ratio becomes near the stoichiometric air-fuel ratio or becomes rich. It has the characteristic to do.

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

  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) to thereby determine the fuel injection amount and fuel of the fuel injection valve 21 according to the engine operating state. The injection timing, the ignition timing of the spark plug 22, and the like are controlled, and the variable valve timing mechanism 39 of the intake valve 37 is controlled so that the actual valve timing of the intake valve 37 is matched with the target valve timing.

  The ECU 30 switches between the stratified combustion mode and the homogeneous combustion mode in accordance with the engine operating state (required 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, and a stratified mixture is formed in the vicinity of the spark 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 fuel into the cylinder during the intake stroke to form a homogeneous mixture and performing homogeneous combustion.

  In general, when the valve overlap in which both the intake valve 37 and the exhaust valve 38 are open increases, the internal EGR amount (the amount of combustion gas remaining in the cylinder) increases. As shown in FIGS. 4 and 5, when heavy fuel is used, smoke increases when the external EGR amount and the internal EGR amount increase beyond the appropriate ranges during the stratified combustion operation. The reason for this is that as the amount of external EGR or internal EGR increases, the amount of fresh air drawn into the cylinder decreases and the combustion temperature decreases. This is because when fuel is used, the combustion state is likely to be unstable in the high EGR region where the external EGR amount and the internal EGR amount are large, and smoke is likely to be generated due to a decrease in the combustion temperature.

  Therefore, the ECU 30 executes the routines of FIG. 2 and FIG. 3 during the stratified combustion operation, thereby using heavy fuel in the high EGR region where the external EGR amount and the valve overlap amount are equal to or greater than the predetermined values A and B. Occasionally, control is made to decrease the external EGR amount and valve overlap amount (internal EGR amount) to increase the intake amount of fresh air into the cylinder and raise the combustion temperature, so that heavy fuel is used The smoke is reduced. Thereby, ECU30 plays the role of the control means said in a claim.

The ECU 30 functions as a fuel property determination means by executing a fuel property determination routine (not shown), and performs injection based on combustion stability (rotational fluctuation) after engine startup, air-fuel ratio deviation during transient operation, and the like. Determine the fuel properties of the fuel. Alternatively, the fuel property of the injected fuel may be determined based on sensor output (evaporation property of fuel) of a fuel property sensor or the like provided in the fuel tank.
Hereinafter, the processing content of each routine of FIG.2 and FIG.3 which ECU30 performs is demonstrated.

[External EGR amount calculation routine]
The external EGR amount calculation routine of FIG. 2 is executed in the control period of the EGR valve 34 during the stratified charge combustion operation. When this routine is started, first, at step 101, the engine rotational speed Ne is read, and at the next step 102, the required torque set based on the accelerator opening is read. Thereafter, the process proceeds to step 103, and the basic external EGR amount EGRB is calculated by a map or a mathematical expression according to the engine operating state (for example, the engine speed Ne and the required torque).

  Thereafter, the routine proceeds to step 104, where it is determined whether or not the fuel used is heavy fuel. As a result, if it is determined that the fuel is not heavy fuel (light fuel), there is no problem of smoke increase or drivability decrease due to heavy fuel. Therefore, the process proceeds to step 107 and the external EGR amount correction amount EGRC is set to the minimum value. Set to (0).

  On the other hand, if it is determined in step 104 that the fuel is heavy, if the amount of external EGR increases too much, there is a problem of increased smoke or reduced drivability. It is determined whether or not the basic external EGR amount EGRB calculated in step 103 is greater than a predetermined value A. As shown in FIG. 4, the predetermined value A is set to an external EGR amount at which the occurrence of smoke becomes noticeable in the high EGR region. This predetermined value A may be set to a fixed value set in advance for the sake of simplification of arithmetic processing. However, the predetermined value A is determined depending on the engine operating state (for example, the engine speed Ne and the required torque) and / or the degree of heavyness. The value A may be calculated by a map or a mathematical expression.

  If it is determined in step 105 that the basic external EGR amount EGRB is equal to or less than the predetermined value A, it is determined that there is no problem of smoke increase or drivability decrease, and the process proceeds to step 107, where the external EGR amount correction amount EGRC is minimized. Set to the value (0).

  On the other hand, if it is determined in step 105 that the basic external EGR amount EGRB is larger than the predetermined value A, the process proceeds to step 106 in order to avoid problems such as an increase in smoke caused by heavy fuel and a decrease in drivability. The external EGR amount correction amount EGRC is calculated by a map or a mathematical formula according to the operating state (for example, the engine speed Ne and the required torque).

  After the external EGR amount correction amount EGRC is determined in step 106 or 107 as described above, the process proceeds to step 108, where the final external EGR amount EGR is obtained by subtracting the external EGR amount correction amount EGRC from the basic external EGR amount EGRB. Thus, when heavy fuel is used, the external EGR amount is reduced by the external EGR amount correction amount EGRC set according to the engine operating state in the high EGR region where the basic external EGR amount EGRB is larger than the predetermined value A. It will be.

[Valve timing calculation routine]
The valve timing calculation routine of FIG. 3 is executed in the control cycle of the variable valve timing mechanisms 39 and 40 during the stratified charge combustion operation. When this routine is started, first, at step 201, the engine rotational speed Ne is read, and at the next step 202, the required torque set based on the accelerator opening is read. Thereafter, the process proceeds to step 203, where the basic valve timing VCTB of the intake valve 37 is calculated by a map or a mathematical expression according to the engine operating state (for example, the engine speed Ne and the required torque).

  Thereafter, the process proceeds to step 204, where it is determined whether or not the used fuel is heavy fuel. As a result, if it is determined that the fuel is not heavy fuel (light fuel), there is no problem of smoke increase or drivability decrease due to heavy fuel, so the process proceeds to step 208 and the valve timing correction amount VCTC is set to the minimum value ( Set to 0).

  On the other hand, if it is determined in step 204 that the fuel is heavy, if the valve overlap amount (internal EGR amount) becomes too large, problems such as an increase in smoke and a decrease in drivability occur. Proceeding to step 205, after calculating the valve overlap amount OL based on the basic valve timing VCTB calculated in step 203, the routine proceeds to step 206, where it is determined whether or not the valve overlap amount OL is greater than a predetermined value B. To do. As shown in FIG. 5, the predetermined value B is set to a valve overlap amount at which the occurrence of smoke becomes noticeable in a region where the valve overlap amount (internal EGR amount) is large. The predetermined value B may be set to a fixed value set in advance for simplification of the arithmetic processing, but is determined according to the engine operating state (for example, the engine speed Ne and the required torque) and / or the degree of heavyness. The value B may be calculated using a map or a mathematical expression.

  If it is determined in step 206 that the valve overlap amount OL is equal to or less than the predetermined value B, it is determined that there is no problem of smoke increase or drivability decrease due to heavy fuel, and the process proceeds to step 208 to determine the valve timing correction amount. VCTC is set to the minimum value (0).

  On the other hand, if it is determined in step 206 that the valve overlap amount OL is larger than the predetermined value B, the process proceeds to step 207 in order to avoid problems such as an increase in smoke due to heavy fuel and a decrease in drivability. The valve timing correction amount VCTC is calculated by a map or a mathematical formula according to the operating state (for example, the engine speed Ne and the required torque).

  After determining the valve timing correction amount VCTC in step 207 or 208 as described above, the process proceeds to step 209 to subtract the valve timing correction amount VCTC from the basic valve timing VCTB to obtain the final valve timing VCT. Thus, when heavy fuel is used, the valve overlap amount (internal EGR amount) is set in accordance with the engine operating state in the operation region where the valve overlap amount OL (internal EGR amount) is larger than the predetermined value B. The amount of decrease is corrected by the timing correction amount VCTC.

  In the first embodiment described above, the external EGR amount and the valve overlap amount when heavy fuel is used in the high EGR region where the external EGR amount and the valve overlap amount are equal to or greater than the predetermined values A and B during the stratified charge combustion operation. In the high EGR region where there is a concern of increased smoke and lower drivability when heavy fuel is used, the amount of fresh air sucked into the cylinder is increased to increase the combustion temperature. The stratified charge combustion can be stably performed even with heavy fuel, and smoke reduction and drivability improvement when using heavy fuel can be realized.

  In the first embodiment, the correction of the external EGR amount and the valve overlap amount when using heavy fuel by the routines of FIGS. 2 and 3 is not performed during the homogeneous combustion operation, but only during the stratified combustion operation. I am trying to do it. This is because the homogeneous combustion operation in which fuel is injected in the intake stroke has a longer time from fuel injection to ignition and the fuel atomization time is longer than the stratified combustion operation in which fuel is injected in the compression stroke. During homogeneous combustion operation, the time required for atomization of heavy fuel can be secured without correction when heavy fuel is used, and the mixing of fuel and air is promoted by the flow of intake air This is because combustion stability can be ensured even with heavy fuel.

  However, it goes without saying that even during the homogeneous combustion operation, either or both of the external EGR amount and the valve overlap amount may be corrected when heavy fuel is used.

  In the first embodiment, the external EGR amount correction amount EGRC and the valve timing correction amount VCTC are calculated according to the engine operating state (for example, the engine speed Ne and the required torque), but the external EGR amount correction amount EGRC is calculated. One of or both of the valve timing correction amount VCTC and the valve timing correction amount VCTC is set to a fixed value set in advance for simplification of calculation processing, or is calculated according to the degree of heavyness or according to the degree of heavyness and the engine operating state. Anyway.

  In the first embodiment, both the external EGR amount and the valve overlap amount are corrected when heavy fuel is used. However, only one of them may be corrected.

  By the way, the external EGR and the internal EGR have an action of increasing the in-cylinder temperature (intake air temperature) and promoting the atomization of the fuel. Therefore, if the external EGR amount or the internal EGR amount becomes too small, the in-cylinder temperature is increased. It becomes lower than the temperature range necessary for atomizing heavy fuel, and when heavy fuel is used, the fuel cannot be atomized sufficiently and piston wet (fuel attached to the piston) increases. As a result, smoke is likely to be generated (see FIGS. 4 and 5).

  Therefore, in the second embodiment of the present invention, by executing the routines of FIGS. 6 and 7 during the stratified charge combustion operation, the external EGR amount and the valve overlap amount (internal EGR amount) are not more than the predetermined values C and D. In the low EGR region, when heavy fuel is used, the external EGR amount and the valve overlap amount are controlled to increase, increasing the in-cylinder temperature, promoting fuel atomization, and using heavy fuel. The smoke is reduced. The processing contents of the routines shown in FIGS. 6 and 7 will be described below.

[External EGR amount calculation routine]
The external EGR amount calculation routine of FIG. 6 is obtained by changing the processing of steps 105 and 108 of the external EGR amount calculation routine of FIG. 2 to the processing of steps 105a and 108a. It is the same as the processing of each step.

  If it is determined in step 104 of this routine that the fuel used is heavy fuel, the routine proceeds to step 105a, where it is determined whether or not the basic external EGR amount EGRB calculated in step 103 is smaller than a predetermined value C. As shown in FIG. 4, the predetermined value C is set to an external EGR amount necessary for reducing smoke in the low EGR region. This predetermined value C may be set to a fixed value set in advance for simplification of the arithmetic processing, but is determined according to the engine operating state (for example, the engine speed Ne and the required torque) and / or the degree of heavyness. The value C may be calculated using a map or a mathematical expression.

  If it is determined in step 105a that the basic external EGR amount EGRB is equal to or greater than the predetermined value C, it is determined that there is no problem of smoke increase or drivability decrease due to heavy fuel, and the process proceeds to step 107 to correct the external EGR amount correction. The quantity EGRC is set to the minimum value (0).

  On the other hand, if it is determined in step 105a that the basic external EGR amount EGRB is smaller than the predetermined value C, the process proceeds to step 106 in order to avoid problems such as an increase in smoke caused by heavy fuel and a decrease in drivability. The external EGR amount correction amount EGRC is calculated by a map or a mathematical formula according to the operating state (for example, the engine speed Ne and the required torque).

  After determining the external EGR amount correction amount EGRC in step 106 or 107 as described above, the process proceeds to step 108a, and the final external EGR amount EGR is obtained by adding the external EGR amount correction amount EGRC to the basic external EGR amount EGRB. Thus, when heavy fuel is used, the external EGR amount is increased and corrected by the external EGR amount correction amount EGRC set according to the engine operating state in the low EGR region where the basic external EGR amount EGRB is less than the predetermined value C. As a result, the in-cylinder temperature rises, fuel atomization is promoted, and smoke during heavy fuel use is reduced.

[Valve timing calculation routine]
The valve timing calculation routine of FIG. 7 is obtained by changing the processing of steps 206 and 209 of the valve timing calculation routine of FIG. 3 to the processing of steps 206a and 209a. This is the same as the step processing.

  If it is determined in step 204 of this routine that the fuel used is heavy fuel, the routine proceeds to step 205, the valve overlap amount OL is calculated, and then the routine proceeds to step 206a, where the valve overlap amount OL is a predetermined value D. Or less. As shown in FIG. 5, the predetermined value D is set to a valve overlap amount necessary for reducing smoke in a region where the valve overlap amount (internal EGR amount) is small. This predetermined value D may be set to a fixed value set in advance for simplification of the arithmetic processing, but is determined according to the engine operating state (for example, the engine speed Ne and the required torque) and / or the degree of heavyness. The value D may be calculated by a map or a mathematical expression.

  If it is determined in step 206a that the valve overlap amount OL is equal to or greater than the predetermined value D, it is determined that there is no problem of smoke increase or drivability decrease due to heavy fuel, and the process proceeds to step 208, where the valve timing correction amount VCTC is set to the minimum value (0).

  On the other hand, if it is determined in step 206a that the valve overlap amount OL is smaller than the predetermined value D, the process proceeds to step 207 in order to avoid problems such as an increase in smoke and a decrease in drivability due to heavy fuel. The valve timing correction amount VCTC is calculated by a map or a mathematical formula according to the operating state (for example, the engine speed Ne and the required torque).

  After determining the valve timing correction amount VCTC in step 207 or 208 as described above, the process proceeds to step 209a, where the valve timing correction amount VCTC is added to the basic valve timing VCTB to obtain the final valve timing VCT. Thus, when heavy fuel is used, the valve overlap amount (internal EGR amount) is set in accordance with the engine operating state in the operation region where the valve overlap amount OL (internal EGR amount) is smaller than the predetermined value D. The increase correction is performed by the timing correction amount VCTC, whereby the in-cylinder temperature is increased, fuel atomization is promoted, and smoke when heavy fuel is used is reduced.

  In the second embodiment, the correction of the external EGR amount and the valve overlap amount when using heavy fuel is not performed during the homogeneous combustion operation, but only during the stratified combustion operation. Needless to say, even during the homogeneous combustion operation, one or both of the external EGR amount and the valve overlap amount may be corrected when heavy fuel is used.

  In the second embodiment, the external EGR amount correction amount EGRC and the valve timing correction amount VCTC are calculated according to the engine operating state (for example, the engine rotational speed Ne and the required torque), but the external EGR amount correction amount EGRC is calculated. One of or both of the valve timing correction amount VCTC and the valve timing correction amount VCTC is set to a fixed value set in advance for simplification of calculation processing, or is calculated according to the degree of heavyness or according to the degree of heavyness and the engine operating state. Anyway.

  In the second embodiment, both the external EGR amount and the valve overlap amount are corrected when heavy fuel is used. However, only one of them may be corrected.

  By the way, the airflow (swirl flow or tumble flow) generated in the cylinder by the airflow control valve 31 has an action of promoting the atomization of the fuel by promoting the mixing of the injected fuel and the air. For this reason, if the strength of the air flow generated in the cylinder is weak during stratified combustion operation, which is inherently poor in atomization of fuel compared to homogeneous combustion operation, fuel atomization is insufficient and the combustion state deteriorates. However, as shown in FIG. 9, there is a problem that smoke increases and torque fluctuation increases and drivability deteriorates.

  Therefore, in the third embodiment of the present invention, by executing the airflow control valve opening calculation routine of FIG. During the stratified combustion operation, when it is determined that the fuel is heavy, the air flow control valve 31 is controlled so as to increase the air flow more than when the light fuel is used, thereby promoting the mixing of the injected fuel and the air and the fuel mist. To stabilize the combustion state of stratified combustion.

  The airflow control valve opening calculation routine of FIG. 8 is executed at the control period of the airflow control valve 31 during engine operation. When this routine is started, first, at step 301, the engine speed Ne is read, and at the next step 302, the required torque set based on the accelerator opening is read. Thereafter, the process proceeds to step 303, and the basic airflow control valve opening SCVB is calculated by a map or a mathematical formula according to the engine operating state (for example, the engine speed Ne and the required torque).

  Thereafter, the process proceeds to step 304, where it is determined whether or not the used fuel is heavy fuel. As a result, if it is determined that the fuel is not a heavy fuel (a light fuel), there is no problem of an increase in smoke or a decrease in drivability due to the heavy fuel, so the routine proceeds to step 307 and the air flow control valve opening correction amount SCVC is set. Set to the minimum value (0).

  On the other hand, if it is determined in step 304 that the fuel is heavy, if the airflow strength becomes too weak, problems such as an increase in smoke and a decrease in drivability occur. It is determined whether the operation is in progress. If it is determined that the operation is not stratified combustion operation (homogeneous combustion operation), it is determined that there is no problem of increased smoke or reduced drivability due to heavy fuel, and step 307 Then, the air flow control valve opening correction amount SCVC is set to the minimum value (0).

  On the other hand, if it is determined in step 305 that the stratified charge combustion operation is being performed, the process proceeds to step 306 in order to avoid problems such as an increase in smoke and a decrease in drivability due to heavy fuel. The air flow control valve opening correction amount SCVC is calculated by a map or a mathematical formula according to the speed Ne and the required torque.

  After determining the airflow control valve opening correction amount SCVC in step 306 or 307 as described above, the process proceeds to step 308, and the airflow control valve opening correction amount SCVC is subtracted from the basic airflow control valve opening SCVB to obtain the final airflow. The control valve opening SCV is obtained. As a result, when heavy fuel is used during the stratified combustion operation, the opening degree of the airflow control valve 31 is reduced by the airflow control valve opening correction amount SCVC set according to the engine operating state, and the airflow intensity is It will be strengthened.

  According to the third embodiment described above, when heavy fuel is used during the stratified combustion operation, the opening degree of the airflow control valve 31 is reduced by the airflow control valve opening degree correction amount SCVC corresponding to the engine operating state. However, since the airflow (swirl flow and tumble flow) generated in the cylinder is strengthened, mixing of fuel and air can be promoted, fuel atomization can be promoted, and even heavy fuel is burned Stability can be ensured, and smoke reduction and drivability improvement can be realized.

In the third embodiment, the airflow control valve opening correction amount SCVC is calculated according to the engine operating state (for example, the engine speed Ne and the required torque), but the airflow control valve opening correction amount SCVC is calculated. For simplification of processing, it may be a fixed value set in advance, or may be calculated according to the degree of heavyness, or according to the degree of heavyness and the engine operating state.
The third embodiment may be implemented in combination with the first embodiment or the second embodiment.

  In the system configuration example of FIG. 1, the variable valve timing mechanism 39 is provided only on the intake side, but a variable valve timing mechanism may be provided on the exhaust side. In addition to the valve timing, The present invention can also be applied to an in-cylinder injection engine equipped with various variable valve mechanisms that vary the valve lift amount and the working angle.

It is a schematic block diagram of the whole engine control system in Example 1 of this invention. 6 is a flowchart illustrating a flow of processing of an external EGR amount calculation routine according to the first embodiment. 3 is a flowchart illustrating a flow of processing of a valve timing calculation routine according to the first embodiment. It is a figure explaining the relationship between the amount of external EGR (EGR valve opening degree) at the time of heavy fuel use, and smoke discharge amount. It is a figure explaining the relationship between the valve overlap amount (internal EGR amount) at the time of heavy fuel use, and a smoke discharge amount. 12 is a flowchart illustrating a flow of processing of an external EGR amount calculation routine according to the second embodiment. 6 is a flowchart illustrating a flow of processing of a valve timing calculation routine according to the second embodiment. 12 is a flowchart illustrating a flow of processing of an airflow control valve opening calculation routine according to the third embodiment. It is a figure explaining the relationship between the airflow control valve opening degree (airflow intensity | strength) at the time of a stratified combustion operation, smoke discharge | emission amount, and a torque fluctuation.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Cylinder injection type engine (cylinder injection type internal combustion engine), 12 ... Intake pipe, 16 ... Throttle valve, 21 ... Fuel injection valve, 22 ... Spark plug, 23 ... Cooling water temperature sensor, 25 ... Exhaust pipe, 30 ... ECU (fuel property determination means, control means), 31 ... airflow control valve, 34 ... EGR valve (exhaust gas recirculation control means), 37 ... intake valve, 38 ... exhaust valve, 39 ... variable valve timing mechanism (variable valve mechanism).

Claims (4)

In a control apparatus for a cylinder injection internal combustion engine in which fuel is injected into a cylinder in an intake stroke or a compression stroke to perform homogeneous combustion or stratified combustion,
An exhaust gas recirculation control means for controlling the flow rate of the external exhaust gas recirculation from the exhaust system to the intake system, and at least one of a variable valve mechanism for varying the opening / closing operation of the intake valve and / or the exhaust valve,
Fuel property determination means for determining the property of the fuel;
When the fuel property determining means determines that the fuel is heavy fuel, the exhaust gas recirculation control means and / or the variable valve mechanism is set to decrease the external exhaust gas recirculation flow rate and / or the valve overlap amount than when the light fuel is used. Control means for controlling;
A control apparatus for a cylinder injection internal combustion engine, comprising: In a control apparatus for a cylinder injection internal combustion engine in which fuel is injected into a cylinder in an intake stroke or a compression stroke to perform homogeneous combustion or stratified combustion,
An exhaust gas recirculation control means for controlling the flow rate of the external exhaust gas recirculation from the exhaust system to the intake system, and at least one of a variable valve mechanism for varying the opening / closing operation of the intake valve and / or the exhaust valve,
Fuel property determination means for determining the property of the fuel;
When the fuel property determination means determines that the fuel is heavy fuel, the exhaust recirculation control means and / or the variable valve mechanism is connected to the external exhaust ring if the external exhaust ring flow rate and / or the valve overlap amount is not more than a predetermined value. And a control means for controlling the flow rate and / or the valve overlap amount in the direction of increasing.   The control device for a direct injection internal combustion engine according to claim 1 or 2, wherein the control means does not execute control according to the fuel property during the homogeneous combustion operation. In a control apparatus for an in-cylinder injection internal combustion engine in which fuel is injected into a cylinder in a compression stroke and stratified combustion is performed,
An airflow control valve for controlling the strength of the airflow generated in the cylinder;
Fuel property determination means for determining the property of the fuel;
Control means for controlling the airflow control valve in a direction in which the airflow is strengthened more than when light fuel is used when the fuel property determination means determines that the fuel is heavy during stratified combustion operation. A control device for a direct injection internal combustion engine.

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