JP2005220857A - Control device for cylinder injection internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure a stable combustion state even when employing heavy fuel in a cylinder injection type engine which switches a combustion mode in accordance with engine rotation speed and load. <P>SOLUTION: When used fuel is judged as heavy fuel during engine operation, a combustion mode switching map for heavy fuel is selected to choose either of a stratified combustion mode, or a homogenious combustion mode as a required combustion mode in accordance with present engine rotation speed and required torque. Data of the combustion mode switching map for heavy fuel are shifted to a side lower in rotation and in load than the combustion mode switching map for light fuel, so that the range on the homogenious combustion mode side of the operation range in the stratified combustion mode during employment of light fuel is changed to the operation range in the homogenious combustion mode. By doing so, the heavy fuel is burned by the homogenious combustion mode in the operation range where the stable stratified combustion of heavy fuel cannot be achieved, which achieves stable combustion 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. Alternatively, as described in Patent Document 1 (Japanese Patent Laid-Open No. 5-52145), in the intermediate region between the stratified combustion mode and the homogeneous combustion mode, fuel is injected into the cylinder in the intake stroke and the compression stroke, respectively. A technique of operating in a two-injection mode for burning is also proposed.

Further, as described in Patent Document 2 (Japanese Patent Laid-Open No. 5-71383), the ratio of the injection amount of the compression stroke to the total injection amount of the intake stroke and the compression stroke in the double injection mode is set according to the target air-fuel ratio. The technology to change is proposed.
JP-A-5-52145 (first page to third page, etc.) Japanese Patent Laid-Open No. 5-71383 (first page to third page, etc.)

  Generally, the combustion mode switching condition (engine speed and load map) for switching the combustion mode is adapted by using a fuel having a standard fuel property (standard fuel). Therefore, the techniques of each of the above patent documents are adapted to the combustion mode switching conditions on the premise that the standard fuel is used, and the 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 stratified combustion mode or double injection, which is inherently narrow in the stable combustion region compared to homogeneous combustion, under the combustion mode switching conditions adapted to the standard fuel When operating in the mode, the injected fuel may not be sufficiently atomized, which may worsen the combustion state and increase smoke emissions or drivability.

  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 in a system that switches the combustion mode according to the engine speed and load. Another object of the present invention is to provide a control device for a direct injection internal combustion engine that can reduce smoke and improve drivability when heavy fuel is used.

  In order to achieve the above object, an invention according to claim 1 is directed to a control apparatus for a direct injection internal combustion engine that switches between a stratified combustion mode and a homogeneous combustion mode according to the engine speed and / or load. Uses light fuel as the combustion mode switching condition to determine engine speed and / or load when switching between stratified combustion mode and homogeneous combustion mode when fuel property is judged by fuel property judgment means and judged as heavy fuel It is made to change to the low rotation side and / or low load side rather than time.

  During operation in the stratified combustion mode, fuel is injected in the compression stroke, so the fuel atomization time from fuel injection to ignition is inherently shortened, and this fuel atomization time depends on the engine speed. The higher it is, the shorter it is. Furthermore, since the fuel injection amount is increased and the fuel injection time becomes longer as the load increases, there is a relationship that the fuel atomization time from the end of injection to ignition becomes shorter as the load increases. On the other hand, the time required to atomize the heavy fuel to a state where stable combustion is possible is longer than that of the light fuel, so when using heavy fuel, the homogeneous combustion mode in the stratified combustion mode operating region is used. In the region on the side, stable stratified combustion is difficult due to the lack of heavy fuel atomization time.

  In view of such circumstances, the present invention changes the combustion mode switching condition to the low rotation side and / or the low load side when using heavy fuel, when using heavy fuel. The region on the homogeneous combustion mode side of the operation region in the stratified combustion mode is changed to the operation region in the homogeneous combustion mode. As a result, in the operation region where heavy fuel cannot be stably stratified, heavy fuel can be burned in the homogeneous combustion mode to stably burn heavy fuel. Reduction and drivability improvement can be realized.

  The present invention is not limited to a system that switches between the two combustion modes of the stratified combustion mode and the homogeneous combustion mode. As in claim 2, the intake air is introduced between the operation region of the stratified combustion mode and the operation region of the homogeneous combustion mode. The present invention can also be applied to a system in which an operation region of a two-injection mode in which fuel is injected into a cylinder and burned in a stroke and a compression stroke, respectively. In this system, when it is determined that the fuel is heavy, the engine speed and / or load when switching between the stratified combustion mode and the double injection mode and when switching between the double injection mode and the homogeneous combustion mode is determined. The combustion mode switching condition may be changed to the low rotation side and / or the low load side than when the light fuel is used. In this case, in the operation region where heavy fuel cannot be stably stratified, heavy fuel is burned in the double injection mode, and further, in the operation region where heavy fuel cannot be stably burned even in the double injection mode (in the compression stroke). In the operation region where the atomization of the heavy fuel to be injected is insufficient, the heavy fuel is burned in the homogeneous combustion mode. In this way, even when switching between the three combustion modes of the stratified combustion mode, the double injection mode, and the homogeneous combustion mode, when the heavy fuel is used, the combustion mode is switched to a combustion mode capable of stably burning the heavy fuel according to the operation region. It is possible to reduce smoke and improve drivability when using heavy fuel.

  By the way, the greater the degree of fuel heaviness, the longer the time required to atomize the fuel to a state where stable fuel combustion is possible. In consideration of this characteristic, a means for determining the degree of heavyness of the used fuel is provided as in claim 3, and the degree to which the combustion mode switching condition is changed to the low rotation side and / or the low load side is determined. You may make it change according to a quality degree. In this way, when using heavy fuel, the degree of reduction of the operation region of the stratified combustion mode, which is a fuel-efficient combustion mode, can be set to the minimum necessary according to the degree of heavyness of the fuel used, Smoke reduction can be realized while preventing excessive fuel consumption deterioration when using heavy fuel.

  Further, in a system that switches between the three combustion modes of the stratified combustion mode, the double injection mode, and the homogeneous combustion mode, as in claim 4, when it is determined that the fuel is heavy, the compression stroke in the double injection mode is determined. The injection amount may be decreased from when light fuel is used to increase the injection amount in the intake stroke. If the injection amount in the compression stroke is reduced, the time required for atomizing the injected fuel in the compression stroke to a state where stable combustion is possible is shortened. Therefore, the compression stroke in the double injection mode is used when heavy fuel is used. If the injection amount is reduced, the combustibility of the two-injection mode can be improved, and smoke can be reduced.

  In this case, as in claim 5, when it is determined that the fuel is heavy, the injection amount in the compression stroke in the double injection mode may be set to the minimum injection amount in the stable injection region of the fuel injection valve. In this way, when heavy fuel is burned in the two-injection mode, it is easy to ensure the fuel atomization time by minimizing the ratio of the compression stroke injection that tends to be short of the fuel atomization time. Since the ratio of intake stroke injection can be maximized, the flammability of heavy fuel can be maximized.

  Further, as in claim 6, there may be provided means for determining the degree of heavyness of the used fuel, and the injection amount in the compression stroke in the double injection mode may be changed according to the degree of heavyness of the used fuel. In this way, when heavy fuel is burned in the two-injection mode, it is possible to avoid an excessive decrease in the injection amount of the compression stroke injection with good fuel efficiency, and a deterioration in fuel consumption due to a decrease in the injection amount of the compression stroke. Can be kept to the minimum necessary.

  Further, as in claim 7, when the ratio of the injection amount of the compression stroke to the total injection amount of the intake stroke and the compression stroke becomes equal to or less than a predetermined value when the double injection mode is executed, the mode is switched to the homogeneous combustion mode. good. In this way, when the heavy fuel is used, the two-injection mode can be switched from the two-injection mode to the homogeneous combustion mode in the operation region where the fuel consumption is worse than the homogeneous combustion mode. Excessive deterioration in fuel consumption can be prevented.

  Further, as in claim 8, the ratio of the injection amount in the compression stroke for switching from the double injection mode to the homogeneous combustion mode may be changed according to the degree of heavyness of the fuel used. In this way, it is possible to switch from the double injection mode to the homogeneous combustion mode at an optimal timing according to the degree of heavyness of the fuel used.

  Several embodiments embodying the best mode for carrying out the present invention will be described below.

  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. In addition, the intake valve 37 and the exhaust valve 38 of the engine 11 are provided with variable valve timing mechanisms 39 and 40 for varying the opening and closing timing, respectively.

  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 for controlling the exhaust gas recirculation amount (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 mechanisms 39 and 40 on the intake side and the exhaust side are controlled so that the actual valve timings of the intake valve 37 and the exhaust valve 38 coincide with the target valve timing. To control.

  The ECU 30 switches between the stratified combustion mode and the homogeneous combustion mode according to the engine rotation speed and the load (required torque). As shown in FIG. 4, the operation region of the stratified combustion mode is set to a lower rotation / low load side than the operation region of the homogeneous combustion mode, and in the stratified combustion mode, a small amount of fuel is directly injected into the cylinder in the compression stroke. Then, the fuel consumption is improved by forming a stratified mixture in the vicinity of the spark plug 22 and stratified combustion. 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.

  During operation in the stratified combustion mode, fuel is injected in the compression stroke, so the fuel atomization time from fuel injection to ignition is inherently shortened, and this fuel atomization time depends on the engine speed. The higher it is, the shorter it is. Furthermore, since the fuel injection amount is increased and the fuel injection time becomes longer as the load increases, there is a relationship that the fuel atomization time from the end of injection to ignition becomes shorter as the load increases. On the other hand, the time required to atomize the heavy fuel to a state where stable combustion is possible is longer than that of the light fuel, so when using heavy fuel, the homogeneous combustion mode in the stratified combustion mode operating region is used. In the region on the side, stable stratified combustion is difficult due to the lack of heavy fuel atomization time.

  In consideration of this point, the ECU 30 determines the fuel property of the fuel used by executing each routine to be described later during engine operation, and when it is determined that the fuel is heavy, the engine speed and the load (request) When the combustion mode is determined based on the torque, the combustion mode switching condition (engine speed and load at the time of switching the combustion mode) is changed to a lower speed side and a lower load side than when light fuel is used. The region on the homogeneous combustion mode side of the operation region in the stratified combustion mode when using the fuel is changed to the operation region in the homogeneous combustion mode (see FIG. 4). As a result, in an operation region where heavy fuel cannot be stably stratified, heavy fuel is burned in a homogeneous combustion mode to stably burn heavy fuel. Hereinafter, processing contents of each routine executed by the ECU 30 will be described.

[Engine control main routine]
The engine control main routine of FIG. 2 is executed at a predetermined cycle during engine operation. When this main routine is started, first, in step 101, a fuel property determination routine (not shown) is executed, which is used 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. The processing in step 101 serves as fuel property determination means in the claims.

  Thereafter, the routine proceeds to step 102, where the required torque is calculated based on the accelerator opening, the engine speed, etc., and then the routine proceeds to step 103, where the required combustion mode determination routine of FIG. To do. Thereafter, in steps 104 to 106, an air system control routine, a fuel system control routine, and an ignition system control routine (not shown) are executed, and control parameters for the air system, the fuel system, and the ignition system are determined in step 103. The target value of the required combustion mode is set, and the injected fuel is burned in the required combustion mode.

[Required combustion mode decision routine]
When the required combustion mode determination routine of FIG. 3 is started in step 102 of the engine control main routine of FIG. 2, first, the engine rotational speed Ne is read in step 111, and in the next step 112, based on the accelerator opening, etc. Read the set required torque. Thereafter, the process proceeds to step 113, where it is determined whether the used fuel is heavy fuel. As a result, if it is determined that the fuel is not heavy fuel (light fuel), the routine proceeds to step 114, where the light fuel combustion mode switching map (see FIG. 4) is selected, and the current engine speed Ne and request are selected. Either the stratified combustion mode or the homogeneous combustion mode is selected as the required combustion mode in accordance with the torque.

  On the other hand, if it is determined in step 113 that the fuel used is heavy fuel, the routine proceeds to step 115, where a combustion mode switching map for heavy fuel (see FIG. 4) is selected and the current fuel is selected. One of the stratified combustion mode and the homogeneous combustion mode is selected as the required combustion mode according to the engine rotational speed Ne and the required torque. The data of the combustion mode switching map for the heavy fuel is shifted to the low rotation side and the low load side than the combustion mode switching map for the light fuel, and is homogeneous in the operation region of the stratified combustion mode when the light fuel is used. The region on the combustion mode side is changed to the operation region in the homogeneous combustion mode. As a result, in the operation region where heavy fuel cannot be stably stratified, heavy fuel can be burned in the homogeneous combustion mode to stably burn heavy fuel. Reduction and drivability improvement can be realized.

  In the above-mentioned steps 113 to 115, the process for switching the combustion mode switching map for heavy fuel and the combustion mode switching map for light fuel depending on whether or not the fuel used is heavy fuel is within the scope of the claims. It serves as a combustion mode switching condition changing means.

  In the first embodiment, the two combustion modes of the stratified combustion mode and the homogeneous combustion mode are switched. However, in the second embodiment of the present invention, as shown in FIG. The two-injection mode operation region in which fuel is injected into the cylinder and burned in the intake stroke and the compression stroke is set between the two operation regions. In the second embodiment, the light fuel combustion mode switching map of FIG. 5A and the heavy fuel combustion mode switching map of FIG. 5B are used. The data of the combustion mode switching map for heavy fuel in FIG. 5B is shifted to the low rotation side and the low load side than the combustion mode switching map for light fuel in FIG.

  Also in the second embodiment, the required combustion mode determination routine that is substantially the same as that in FIG. 3 is executed to determine 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), the light fuel combustion mode switching map of FIG. 5A is selected, and the current engine speed Ne and the required torque are selected. One of the three combustion modes of the stratified combustion mode, the double injection mode, and the homogeneous combustion mode is selected as the required combustion mode.

  In contrast, if it is determined that the fuel used is heavy fuel, the heavy fuel combustion mode switching map shown in FIG. 5B is selected, and the current engine speed Ne and the required torque are selected. Accordingly, one of the three combustion modes is selected as the required combustion mode. The data of the combustion mode switching map for heavy fuel is shifted to the low rotation side and the low load side than the combustion mode switching map for light fuel. As a result, the region on the double injection mode side of the operation region in the stratified combustion mode when the light fuel is used is changed to the operation region in the double injection mode, and the width of the operation region in the double injection mode is narrowed. The operation region of the homogeneous combustion mode is expanded to the double injection mode side.

  According to the second embodiment described above, in the operation region where the heavy fuel cannot be stably stratified, the heavy fuel is burned in the double injection mode, and the heavy fuel is stably burned even in the double injection mode. In an operation region where operation is not possible (operation region in which atomization of heavy fuel injected in the compression stroke is insufficient), heavy fuel is burned in the homogeneous combustion mode. For this reason, even when switching the three combustion modes of the stratified combustion mode, the double injection mode, and the homogeneous combustion mode, when using heavy fuel, it is possible to switch to a combustion mode in which heavy fuel can be stably burned according to the operating region. It is possible to reduce smoke and improve drivability when using heavy fuel (see FIG. 6).

  In each of the first and second embodiments, the combustion mode switching map is set to two types for heavy fuel and light fuel. However, the degree of heavyness of the fuel used is divided into three or more levels. Accordingly, three or more types of combustion mode switching maps may be set, and the required combustion mode may be determined by selecting a map corresponding to the degree of heavyness of the used fuel from these maps. Alternatively, only a combustion mode switching map for a standard fuel (for example, light fuel) is set, and data of the combustion mode switching map for the standard fuel (engine speed Ne at the time of switching the combustion mode, request) during engine operation. Torque) is corrected by a correction coefficient or the like according to the degree of heavyness of the fuel used, so that a combustion mode switching map corresponding to the degree of heavyness of the fuel used is automatically created to determine the required combustion mode. Also good.

  As described above, if the combustion mode switching map is selected or corrected according to the degree of heavyness of the fuel used, the degree of change of the data of the combustion mode switching map to the low rotation side and the low load side is determined. Since it can be changed according to the degree of quality, when using heavy fuel, the degree of reduction in the operation area of the stratified combustion mode and the double injection mode, which is a fuel-efficient combustion mode, depends on the degree of heavyness of the fuel used. Therefore, smoke can be reduced while preventing excessive deterioration in fuel consumption when using heavy fuel.

  In addition, only the combustion mode switching map for standard fuel (for example, light fuel) is set, and the current engine speed Ne and the required torque are corrected by a correction coefficient or the like according to the degree of heavyness of the fuel used, and after correction The engine speed Ne and the required torque may be compared with the data of the combustion mode switching map for standard fuel to determine the required combustion mode. In this case, the same effect as described above can be obtained.

  In the first and second embodiments, when the heavy fuel is used, the combustion mode switching condition is changed to both the low rotation side and the low load side, but either the low rotation side or the low load side is used. You may make it change only to the side.

  In the third embodiment of the present invention, for example, using the combustion mode switching map of FIG. 5A, there are three types of stratified combustion mode, double injection mode, and homogeneous combustion mode according to the current engine speed Ne and the required torque. In a system in which any one of the combustion modes is selected as the required combustion mode, when the fuel used is determined to be heavy fuel during operation in the double injection mode, the injection amount of the compression stroke in the double injection mode is set. The injection amount in the intake stroke is increased by decreasing the amount. If the injection amount in the compression stroke is reduced, the time required for atomizing the injected fuel in the compression stroke to a state where stable combustion is possible is shortened. Therefore, the compression stroke in the double injection mode is used when heavy fuel is used. If the injection amount is reduced, the combustibility of the two-injection mode can be improved, and smoke can be reduced.

  The control in the double injection mode is executed by the injection amount calculation routine in the double injection mode in FIG. This routine is executed by the ECU 30 at a predetermined cycle during engine operation, and serves as a double injection mode control means in the claims. 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. After this, the routine proceeds to step 203, where it is determined whether or not the current combustion mode is the double injection mode. If it is not the double injection mode, this routine is terminated without performing the subsequent processing.

  On the other hand, when it is determined in step 203 that the current combustion mode is the double injection mode, the routine 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), the routine proceeds to step 205 where the ratio of the compression stroke injection quantity (compression stroke injection ratio) K to the total injection quantity Qall of the intake stroke and the compression stroke is set. Then, it is calculated by a map or mathematical formula according to the current engine speed Ne and the required torque. After this, the routine proceeds to step 206, where the total injection amount Qall is multiplied by the compression stroke injection ratio K to determine the compression stroke injection amount QC.

  On the other hand, if it is determined in step 204 that the fuel used is heavy fuel, the routine proceeds to step 207, where the minimum injection amount QCmin of the compression stroke in the double injection mode is determined according to the current engine speed Ne and the required torque. Calculate by map or mathematical formula. The minimum injection amount QCmin corresponds to the minimum injection amount in a region where the injection state of the fuel injection valve 21 is stable (stable injection region). Thereafter, the process proceeds to step 208, and a correction coefficient KQC for correcting the minimum injection amount QCmin in the compression stroke according to the degree of heavyness of the fuel used is calculated by a map or numerical formula using the degree of fuel heavyness as a parameter. Thereby, the correction coefficient KQC is set to a smaller value in the range of 0 <KQC ≦ 1 as the fuel used becomes heavier. Thereafter, the process proceeds to step 209, where the compression stroke injection quantity QC is obtained by multiplying the compression stroke minimum injection quantity QCmin calculated in step 207 by the correction coefficient KQC.

  After calculating the compression stroke injection quantity QC in step 206 or 209 as described above, the routine proceeds to step 210, where the compression stroke injection quantity QC is subtracted from the total injection quantity Qall to obtain the intake stroke injection quantity QI. .

  According to the third embodiment described above, the injection amount in the compression stroke in the double injection mode is set to the minimum injection amount in the stable injection region of the fuel injection valve 21 when it is determined that the fuel is heavy. Ratio of intake stroke injection that makes it easy to ensure fuel atomization time by minimizing the ratio of compression stroke injection that tends to be short of fuel atomization time when burning heavy fuel in double injection mode Can be maximized, the flammability of heavy fuel can be improved to the maximum, and smoke can be reliably reduced.

  Moreover, in the third embodiment, since the minimum injection amount in the compression stroke in the double injection mode is corrected with the correction coefficient KQC according to the degree of heavyness, when heavy fuel is burned in the double injection mode. Further, it is possible to avoid an excessive decrease in the injection amount of the compression stroke injection with good fuel consumption, and it is possible to minimize deterioration of the fuel consumption due to a decrease in the injection amount of the compression stroke.

  However, in the present invention, the minimum injection amount in the compression stroke calculated in step 207 may be used as it is as the final injection amount in the compression stroke without being corrected according to the degree of heavyness. Smoke can be reduced as compared with the conventional system that determines the injection amount in the compression stroke without using it.

  Further, the injection amount in the compression stroke in the double injection mode when using heavy fuel does not necessarily have to be reduced to the minimum injection amount in the stable injection region of the fuel injection valve 21. For example, the compression stroke in the double injection mode The injection amount may be reduced only when light fuel is used depending on the engine operating state (engine speed Ne, required torque, etc.) and / or the degree of fuel heavyness. If the injection amount in the compression stroke in the double injection mode is decreased when heavy fuel is used than when the light fuel is used, the combustibility in the double injection mode can be improved as compared with the conventional case.

  By the way, the double injection mode is a combustion mode in which the requested fuel amount is divided and injected into the intake stroke and the compression stroke, and fuel consumption is gained by the compression stroke injection. There is a relationship that the fuel efficiency rate in the mode becomes worse as the compression stroke injection ratio K decreases. Therefore, in the double injection mode, if the compression stroke injection ratio K becomes too small, the negative effect (output reduction) of the compression stroke injection exceeds the positive effect (improves fuel consumption), and the fuel efficiency rate in the double injection mode increases. It becomes worse than the fuel consumption rate in the homogeneous combustion mode.

  Therefore, in Example 4 of the present invention, the compression stroke injection ratio K at the point (D) where the fuel consumption rate in the double injection mode becomes substantially the same as the fuel consumption rate in the homogeneous combustion mode is determined beforehand by test data, design data, or the like. This is determined and set as the switching determination value D. As shown in FIG. 10, when the compression stroke injection ratio K falls below the switching determination value D during the operation in the double injection mode, the double injection mode is set. Is switched to the homogeneous combustion mode.

  This control is executed by the injection amount calculation routine in the double injection mode in FIG. In this routine, the processing of steps 211 to 213 is added between step 209 and step 210 of the injection amount calculation routine in the double injection mode in FIG. 7. It is the same as the processing of each step.

  In this routine, when heavy fuel is used, the compression stroke injection amount QC is calculated by the processing of steps 207 to 209, and then the process proceeds to step 211, where the compression stroke injection amount QC is divided by the total injection amount Qall. The injection ratio K is obtained. Thereafter, the routine proceeds to step 212, where it is determined whether or not the compression stroke injection ratio K is below the switching determination value D. If the compression stroke injection ratio K is not below the switching determination value D, the one in the double injection mode Is determined to have better fuel efficiency than the homogeneous combustion mode, and the operation in the two-injection mode is continued.

  On the other hand, if it is determined in step 212 that the compression stroke injection ratio K is lower than the switching determination value D, it is determined that the homogeneous combustion mode has better fuel consumption than the double injection mode. In step 213, the required combustion mode is switched from the twice injection mode to the homogeneous combustion mode.

  In the fourth embodiment described above, since the compression stroke injection ratio K is switched from the double injection mode to the homogeneous combustion mode when the compression stroke injection ratio K falls below the switching determination value D during operation in the double injection mode, In the operating region where the fuel consumption is worse in the double injection mode than in the homogeneous combustion mode when using fuel, the double injection mode can be switched to the homogeneous combustion mode, and excessive fuel consumption deterioration due to the double injection mode can be prevented. Can do.

  In the fourth embodiment, the switching determination value D is a fixed value obtained in advance by test data, design data, or the like. However, the switching determination value D increases as the fuel used becomes heavier. The value D may be changed according to the degree of heavyness of the fuel used. In this way, it is possible to switch from the double injection mode to the homogeneous combustion mode at an optimal timing according to the degree of heavyness of the fuel used.

  Needless to say, the present invention may be implemented by combining the second embodiment and the third embodiment (or 4).

It is a schematic block diagram of the whole engine control system in Example 1 of this invention. 6 is a flowchart showing a flow of processing of an engine control main routine according to the first embodiment. 3 is a flowchart showing a flow of processing of a required combustion mode determination routine of Embodiment 1. It is a figure explaining the relationship between the combustion mode switching map for heavy fuels and the combustion mode switching map for light fuels of Example 1. FIG. (A) And (b) is a figure explaining the relationship between the combustion mode switching map for heavy fuels of the Example 2, and the combustion mode switching map for light fuels. It is a figure explaining the relationship between the smoke emission amount and fuel properties in the double injection mode and the stratified combustion mode. 12 is a flowchart showing a flow of processing of an injection amount calculation routine in a two-injection mode according to a third embodiment. 12 is a flowchart showing a flow of processing of an injection amount calculation routine in a double injection mode according to a fourth embodiment. It is a figure explaining the relationship between the fuel consumption rate at the time of 2 injection mode, and the compression stroke injection ratio K. FIG. 6 is a time chart showing an example of switching from a double injection mode to a homogeneous combustion mode in Example 4.

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 (combustion mode switching condition changing means, fuel property detecting means, double injection mode control means), 37 ... intake valve, 38 ... exhaust valve, 39, 40 ... variable valve timing mechanism

Claims (8)

A cylinder that switches between a stratified combustion mode in which fuel is injected into the cylinder in the compression stroke and stratified combustion, and a homogeneous combustion mode in which fuel is injected into the cylinder in the intake stroke to perform homogeneous combustion according to the engine speed and / or load. In a control device for an internal injection internal combustion engine,
Fuel property determination means for determining the fuel property of the fuel used;
The combustion mode switching condition for switching between the stratified combustion mode and the homogeneous combustion mode when the fuel property determining means determines that the fuel is heavy is changed to a lower rotation side and / or a lower load side than when using light fuel. A control device for a direct injection internal combustion engine, comprising: a combustion mode switching condition changing means. Between the operation region of the stratified combustion mode in which fuel is injected into the cylinder in the compression stroke and stratified combustion, and the operation region of the homogeneous combustion mode in which fuel is injected into the cylinder in the intake stroke and homogeneous combustion is performed, Control of a cylinder injection type internal combustion engine that sets an operation region of a two-injection mode in which fuel is injected into the cylinder in the compression stroke and burns, and switches these three combustion modes according to the engine speed and / or load. In the device
Fuel property determination means for determining the fuel property of the fuel used;
Combustion mode switching conditions for executing switching between the stratified combustion mode and the two-time injection mode and switching between the two-time injection mode and the homogeneous combustion mode when the fuel property determining means determines heavy fuel. A control device for a cylinder injection type internal combustion engine, comprising: a combustion mode switching condition changing means for changing to a low rotation side and / or a low load side as compared to when light fuel is used. The fuel property determining means includes means for determining the degree of heavyness of the fuel used,
The combustion mode switching condition changing means changes the degree of changing the combustion mode switching condition to a low rotation side and / or a low load side according to the degree of heavyness of the fuel used. The control apparatus for a cylinder injection internal combustion engine according to claim 1. Between the operation region of the stratified combustion mode in which fuel is injected into the cylinder in the compression stroke and stratified combustion, and the operation region of the homogeneous combustion mode in which fuel is injected into the cylinder in the intake stroke and homogeneous combustion is performed, Control of a cylinder injection type internal combustion engine that sets an operation region of a two-injection mode in which fuel is injected into the cylinder in the compression stroke and burns, and switches these three combustion modes according to the engine speed and / or load. In the device
Fuel property determination means for determining the fuel property of the fuel used;
A double injection mode control means for increasing the injection amount of the intake stroke by decreasing the injection amount of the compression stroke in the double injection mode when using the light fuel when the fuel property determining means determines that the fuel is heavy. A control device for a direct injection internal combustion engine, comprising:   The double injection mode control means sets the injection amount in the compression stroke in the double injection mode to the minimum injection quantity in the stable injection region of the fuel injection valve when the fuel property determination means determines heavy fuel. The control apparatus for a direct injection internal combustion engine according to claim 4, wherein the control apparatus is a cylinder injection internal combustion engine. The fuel property determining means includes means for determining the degree of heavyness of the fuel used,
The in-cylinder injection internal combustion engine according to claim 4 or 5, wherein the double injection mode control means changes the injection amount of the compression stroke in the double injection mode in accordance with the degree of heavyness of the fuel used. Engine control device.   The double injection mode control means switches to the homogeneous combustion mode when the ratio of the injection amount of the compression stroke to the total injection amount of the intake stroke and the compression stroke becomes equal to or less than a predetermined value when the double injection mode is executed. The control device for a direct injection internal combustion engine according to any one of claims 4 to 6. The fuel property determining means includes means for determining the degree of heavyness of the fuel used,
The said double injection mode control means changes the ratio of the injection amount of the compression stroke which switches from the said double injection mode to the said homogeneous combustion mode according to the heavy degree of use fuel, It is characterized by the above-mentioned. The control apparatus for a direct injection internal combustion engine.

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