JP2005155480A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine capable of minimizing the exhaustion of NOx while securing excellent operability. <P>SOLUTION: The ECU 2 of this control device 1 switches a combustion mode between a uniform combustion mode and a stratified combustion mode, and performs fuel injection two times while both combustion modes are being switched. The ECU 2 terminates two times of fuel injection according to the results of the comparison of a fuel injection amount TCYLLMT for transfer calculated according to a requested torque PMCMD against a fuel injection amount TCYLISTT for intake stroke calculated according to an intake air amount during the two times of fuel injection in switching the combustion mode from the stratified combustion mode to the uniform combustion mode (step 124). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention switches the combustion mode of an internal combustion engine between a uniform combustion mode and a stratified combustion mode, and performs in-cylinder injection type in which fuel injection is performed twice during the transition between the two combustion modes. The present invention relates to a control device for an internal combustion engine.

  Conventionally, as this type of control device, for example, the one described in Patent Document 1 is known. In this control device, as a combustion mode of the internal combustion engine, a uniform combustion mode in which fuel injection is performed during the intake stroke, a stratified combustion mode in which the fuel injection is performed during the compression stroke, and a fuel injection during the intake stroke and the compression stroke within one combustion cycle. Each has a two-injection combustion mode. From these three combustion modes, any one of the combustion modes is selected according to the engine speed and the target torque, and the double injection combustion mode is a torque generated when switching between the stratified combustion mode and the uniform combustion mode. In order to suppress the step, it is executed during the transition between both combustion modes.

  In the two-injection combustion mode, fuel injection control is executed as follows. That is, first, the total fuel injection amount for two injections is calculated based on the intake air amount and the engine speed. Next, for example, the fuel injection amount to be injected during the compression stroke is set to a predetermined constant value, and the value obtained by subtracting the fuel injection amount from the total fuel injection amount is used as the fuel injection amount to be injected during the intake stroke. Set. Then, the fuel injection control is executed based on the fuel injection amounts for the compression stroke injection and the intake stroke injection set as described above.

  The above control device has the following problems. That is, in the two-injection combustion mode of this control device, the fuel injection amount for compression stroke injection is set to a constant value, so that mixing suitable for combustion in the two-injection combustion mode is performed depending on the operating state of the internal combustion engine. Qi may not be generated. Specifically, when the operating state of the internal combustion engine during the two-injection combustion mode, particularly when the engine speed changes, the flow state of the air in the cylinder changes, and accordingly, the minimum ignitable during the compression stroke The fuel injection amount changes. When the minimum fuel injection amount changes in this manner, in this control device, the fuel injection amount for compression stroke injection remains a constant value, and therefore, an air-fuel mixture suitable for stable combustion cannot be generated. As a result, the combustion state during the two-injection combustion mode becomes unstable, which leads to deterioration in drivability due to torque fluctuations of the internal combustion engine.

  In the above control device, since the three combustion modes are selected using the target torque and the engine speed as parameters, the two-injection combustion mode is set as long as these parameters are within the execution region of the two-injection combustion mode. Will continue. In the two-injection combustion mode, fuel is injected during the compression stroke in addition to the intake stroke, so that a rich air-fuel mixture is generated in the vicinity of the spark plug and thinner around it. For this reason, at the time of combustion, by starting to burn from a rich air-fuel mixture, the propagation speed of the flame is increased, so that the combustion temperature is higher than in the uniform combustion mode. As a result, when the two-injection combustion mode is continuously executed for a long time, there is a problem that the amount of NOx emission increases.

  The present invention has been made to solve the above-described problems, and provides an internal combustion engine control device capable of suppressing NOx emission to a minimum while ensuring good operability. With the goal.

JP-A-11-82135

  The control apparatus for an internal combustion engine according to claim 1 of the present invention switches the combustion mode between a uniform combustion mode in which fuel injection into the cylinder 10 is performed during the intake stroke and a stratified combustion mode in which fuel injection is performed during the compression stroke. And injecting fuel during the intake stroke and the compression stroke in one combustion cycle during the transition during the switching of the combustion mode between the uniform combustion mode and the stratified combustion mode, respectively. A control device 1 for an in-cylinder injection internal combustion engine 3 to be executed, the operation state detection means for detecting the operation state of the internal combustion engine 3 (the same in the embodiment (hereinafter the same in this section)) ECU 2, crank angle sensor 22, The air flow sensor 24, the intake pipe absolute pressure sensor 26, the accelerator opening sensor 30), and a request for calculating the required torque of the internal combustion engine 3 according to the detected operating state of the internal combustion engine 3. In accordance with the torque calculation means (ECU 2, step 1 in FIG. 2) and the calculated required torque, the combustion mode determination means (ECU 2, FIG. 2) determines the combustion mode to be either the uniform combustion mode or the stratified combustion mode. Step 2) and a transition-time fuel injection amount calculating means (ECU2, FIG. 3) for calculating a transition-time fuel injection amount (temporary required fuel injection amount TCYLLMT) to be injected during the transition according to the calculated required torque Step 13), intake air amount detection means (air flow sensor 24) for detecting the intake air amount, and fuel injection amount for intake stroke (intake stroke) to be injected during the intake stroke according to the detected intake air amount Intake stroke fuel injection amount calculation means (ECU 2, step 11 in FIG. 3) for calculating the required fuel injection amount TCYL1STT for injection, and the uniform combustion mode from the stratified combustion mode The fuel injection end means (ECU2, FIG. 10) for ending the fuel injection twice according to the comparison result between the fuel injection amount for transition and the fuel injection amount for intake stroke And step 124).

  According to this configuration, the required torque is calculated according to the operating state of the internal combustion engine, and the combustion mode is determined to be the uniform combustion mode or the stratified combustion mode according to the required torque. In the uniform combustion mode, fuel is injected during the intake stroke, and in the stratified combustion mode, fuel is injected during the compression stroke. Further, during the transition between the two combustion modes, the fuel is injected during the intake stroke and the compression stroke in one combustion cycle in order to ensure stable combustion and suppress the occurrence of a torque step. Perform fuel injection twice. Further, the fuel injection amount for transition to be injected during the transition at the time of switching between the two combustion modes is calculated according to the calculated required torque, and during the intake stroke according to the detected intake air amount. The fuel injection amount for the intake stroke to be injected is calculated. Then, during the two-time fuel injection when switching from the stratified combustion mode to the uniform combustion mode, the second-time fuel injection is terminated according to the comparison result between the transition-time fuel injection amount and the intake stroke fuel injection amount.

  Thus, the reason for terminating the fuel injection twice in accordance with the comparison result between the fuel injection amount for transition and the fuel injection amount for intake stroke is as follows. That is, in the stratified combustion mode, the intake air amount is very large and combustion is performed at an extremely lean air-fuel ratio. On the other hand, in the uniform combustion mode, the intake air amount is smaller than in the stratified combustion mode and the rich air-fuel ratio is increased. Combustion takes place. Therefore, when the combustion mode is switched from the stratified combustion mode to the uniform combustion mode, it is necessary to reduce the intake air amount. However, the intake air amount is changed to the combustion mode after switching, that is, uniform because of the response delay of the throttle valve. It takes time to converge to a value suitable for the combustion mode. Therefore, the fuel injection amount for the intake stroke calculated according to the intake air amount gradually decreases as the intake air amount decreases. Thus, during the transition to the switching to the uniform combustion mode, the intake stroke fuel injection amount decreases as the intake air amount decreases and approaches the transition fuel injection amount. As described above, when the fuel injection amount for the intake stroke approaches the fuel injection amount for the transition time, the air-fuel ratio is richer than that in the stratified combustion mode, and the execution of the uniform combustion mode can be started. In other words, when the torque level difference does not occur and stable combustion in the uniform combustion mode can be secured, the fuel injection can be executed twice more than necessary by terminating the fuel injection twice. Accordingly, NOx emission can be suppressed to a minimum while ensuring good drivability.

  According to a second aspect of the present invention, in the control device for an internal combustion engine according to the first aspect, the two-time fuel injection end means (ECU2) is a ratio of the fuel injection amount for transition and the fuel injection amount for intake stroke (TCYLLMT / TCYL1STT). ) Is larger than a predetermined value (KCMDDSC / KCMD1ST), the fuel injection is terminated twice.

  According to this configuration, the degree of approach between the two can be obtained by the ratio between the fuel injection amount for transition and the fuel injection amount for intake stroke. The end timing of injection can be determined easily and appropriately.

  According to a third aspect of the invention, in the control device for an internal combustion engine according to the first or second aspect, the operating state detecting means is a rotational speed detecting means (ECU2, crank angle) for detecting the rotational speed of the internal combustion engine (engine rotational speed NE). The transition-time fuel injection amount calculation means includes a sensor 22), and the fuel injection amount calculation means for the transition time is set to the detected number of revolutions of the internal combustion engine by changing the fuel injection amount during the compression stroke of the second fuel injection (fuel amount TIMDSC for compression stroke injection). It is calculated according to this.

  According to this configuration, even when the flow state of the air in the cylinder changes with the change in the rotational speed of the internal combustion engine during the second fuel injection, the fuel injection amount during the compression stroke of the second fuel injection is It is possible to set appropriately while reflecting the change of the flow state. Thereby, more stable combustion can be ensured during the fuel injection twice, and as a result, better drivability can be ensured.

  According to a fourth aspect of the present invention, in the control device for an internal combustion engine according to the first to third aspects, the two-time fuel injection ending means performs the fuel injection amount for transition after the second time fuel injection is executed for a predetermined time TMDSCMDS1. The fuel injection amount for the intake stroke is compared.

  According to this configuration, after the fuel injection is performed twice for a predetermined time, the transition-time fuel injection amount and the intake stroke fuel injection amount for determining the end timing are compared. That is, at the time of switching to the uniform combustion mode, fuel injection is executed at least for a predetermined time, so that the effect obtained by executing the fuel injection twice can be ensured.

  The invention according to claim 5 is the control device for an internal combustion engine according to claim 4, wherein the internal combustion engine recirculates exhaust gas to the intake side of the internal combustion engine (EGR pipe 15), and the EGR passage. It has an EGR valve (EGR control valve 16) that opens and closes, and the predetermined time is set according to the responsiveness of the EGR valve.

  According to this configuration, the predetermined time, that is, the time for executing at least two fuel injections is set according to the responsiveness of the EGR valve. In general, the EGR valve has the worst response among the devices directly related to the combustion state of the internal combustion engine, and has a large influence on the combustion state. Further, the EGR amount by the EGR valve is controlled so as to be large in the stratified combustion mode and small in the uniform combustion mode. For this reason, when switching from the stratified combustion mode to the uniform combustion mode, it takes time for the EGR amount to converge to a value suitable for the uniform combustion mode. Therefore, by setting the predetermined time according to the responsiveness of the EGR valve, it is possible to ensure the effect of executing the fuel injection twice while reflecting the responsiveness of the EGR valve.

1 is a diagram illustrating a schematic configuration of a control device according to an embodiment of the present invention and an internal combustion engine to which the control device is applied. It is a flowchart which shows the main routine of a fuel-injection control process. It is a flowchart which shows the subroutine for calculating the request | requirement fuel injection amount TCYL. It is a flowchart which shows the subroutine for calculating the request | requirement fuel injection quantity TCYL1STT for intake stroke injection. It is a flowchart which shows the subroutine for calculating the request | requirement fuel injection quantity TCYL2NDT for compression stroke injection. It is a flowchart which shows a part of subroutine for calculating provisional request | requirement fuel injection amount TCYLLMT. It is a flowchart following the subroutine of FIG. It is a flowchart which shows the subroutine for calculating virtual target air fuel ratio KCMDIMG. It is a flowchart which shows the subroutine for performing fuel injection. It is a flowchart which shows a part of subroutine for setting the combustion transfer mode flag F_DSCMOD. FIG. 11 is a flowchart following the subroutine of FIG. 10. FIG. It is a flowchart which shows the subroutine for setting the double injection flag F_DBLINJ. It is a figure which shows an example of the TIMDSC table for calculating the fuel amount TIMDSC for compression stroke injection. It is a figure which shows an example of the map for calculating required torque PMCMD. It is a figure which shows an example of the map for setting the stratified combustion permission flag F_DISCOK.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a schematic configuration of a control device 1 according to an embodiment of the present invention and an internal combustion engine (hereinafter referred to as “engine”) 3 to which the control device 1 is applied. As shown in the figure, the control device 1 includes an ECU 2. The ECU 2 performs a fuel injection control process for the internal combustion engine 3 and the like, as will be described later.

  The engine 3 is an in-line four-cylinder (only one is shown) type gasoline engine mounted on a vehicle (not shown), and a combustion chamber 3c is formed between a piston 3a and a cylinder head 3b of each cylinder 10. A recess 3d is formed at the center of the upper surface of the piston 3a. A fuel injection valve (hereinafter referred to as “injector”) 4 and a spark plug 5 are attached to the cylinder head 3b so as to face the combustion chamber 3c, and fuel is directly injected into the combustion chamber 3c. That is, the engine 3 is of a cylinder injection type.

  The injector 4 is disposed in the center of the top wall of the combustion chamber 3c, and is connected to the high-pressure pump 4a via the fuel pipe 4b. The fuel is boosted by a high-pressure pump 4 a from a fuel tank (not shown), and then supplied to the injector 4 in a state of being regulated by a regulator (not shown), and through this injector 4, a recess 3 d of the piston 3 a. It is jetted toward. As a result, the fuel collides with the upper surface of the piston 3a including the recess 3d to form a fuel jet. In particular, during stratified combustion, which will be described later, most of the injected fuel collides with the recess 3d to form a fuel jet. The injector 4 is electrically connected to the ECU 2 and, as will be described later, a fuel injection time and a fuel injection timing (valve opening timing and valve closing timing) that are valve opening times according to a drive signal from the ECU 2. Is controlled. The fuel injection time of the injector 4 corresponds to the amount of fuel injected into the cylinder 10, that is, the fuel injection amount. In the following description, the fuel injection time of the injector 4 is referred to as the fuel injection amount.

  A fuel pressure sensor 20 is attached in the vicinity of the injector 4 of the fuel pipe 4b. The fuel pressure sensor 20 detects the fuel pressure PF of the fuel injected by the injector 4 and outputs a detection signal to the ECU 2. In addition, a fuel temperature sensor 21 is electrically connected to the ECU 2, and the fuel temperature sensor 21 detects the fuel temperature TF and outputs a detection signal to the ECU 2.

  Further, the spark plug 5 is also electrically connected to the ECU 2, and the ECU 2 discharges when a high voltage is applied at a timing according to the ignition timing, whereby the air-fuel mixture in the combustion chamber 3c burns. .

  The engine 3 is of the DOHC type and includes an intake camshaft 6 and an exhaust camshaft 7. These intake and exhaust camshafts 6 and 7 have an intake cam 6a and an exhaust cam 7a for opening and closing the intake valve 8 and the exhaust valve 9, respectively. The intake and exhaust camshafts 6 and 7 are connected to the crankshaft 3e via a timing belt (not shown). The intake and exhaust camshafts 6 and 7 rotate once every two rotations according to the rotation of the crankshaft 3e.

  A magnet rotor 22a is attached to the crankshaft 3e. The magnet rotor 22a, together with the MRE pickup 22b, constitutes a crank angle sensor 22 (operating state detection means, rotation speed detection means). The crank angle sensor 22 outputs a CRK signal and a TDC signal, both of which are pulse signals, to the ECU 2 as the crankshaft 3e rotates. One pulse of the CRK signal is output every predetermined crank angle (for example, 30 °). The ECU 2 calculates the engine speed (hereinafter referred to as “engine speed”) NE of the engine 3 based on the CRK signal. On the other hand, the TDC signal is a signal indicating that the piston 3a of each cylinder 10 is at a predetermined crank angle position near the TDC (top dead center) at the start of the intake stroke. In this example of the four-cylinder type, the crank angle 180 One pulse is output every °.

  A water temperature sensor 23 is attached to the main body of the engine 3. The water temperature sensor 23 is composed of a thermistor, detects an engine water temperature TW that is the temperature of the cooling water circulating in the main body of the engine 3, and outputs a detection signal to the ECU 2.

  The intake pipe 12 of the engine 3 is provided with an air flow sensor 24, a throttle valve mechanism 13, a throttle valve opening sensor 25, an intake pipe absolute pressure sensor 26, and the like in order from the upstream side.

  The air flow sensor 24 (intake air amount detection means) is composed of a hot-wire air flow meter, and detects a detection signal representing an intake air amount (hereinafter referred to as “TH passage intake air amount”) GTH passing through a throttle valve 13a described later. It outputs to ECU2.

  The throttle valve mechanism 13 includes a throttle valve 13a and an actuator 13b that opens and closes the throttle valve 13a. The throttle valve 13a is rotatably provided in the middle of the intake pipe 12, and the TH passing intake air amount GTH changes according to the opening degree change accompanying the rotation. The actuator 13b is configured by combining a motor and a gear mechanism (both not shown). When the motor is driven by a control signal from the ECU 2, the opening of the throttle valve 13a (hereinafter referred to as "throttle valve opening"). ") TH changes.

  Further, the throttle valve opening sensor 25 (operating state detection means) is constituted by, for example, a potentiometer, detects the throttle valve opening TH, and outputs a detection signal to the ECU 2. The intake pipe absolute pressure sensor 26 (operating state detection means) is constituted by a semiconductor pressure sensor or the like, detects the intake pipe absolute pressure PBA, which is the absolute pressure in the intake pipe 12, and sends the detection signal to the ECU 2. Output. The intake pipe 12 is provided with an intake air temperature sensor 27. The intake air temperature sensor 27 is composed of a thermistor, detects the intake air temperature TA in the intake pipe 12, and outputs a detection signal to the ECU 2.

  An EGR pipe 15 is connected between the intake pipe 12 downstream of the throttle valve mechanism 13 and the exhaust pipe 14 upstream of the catalyst device 17. This EGR pipe 15 recirculates the exhaust gas of the engine 3 to the intake side, thereby lowering the combustion temperature in the combustion chamber 3c, thereby executing an EGR operation for reducing NOx in the exhaust gas. Is. An EGR control valve 16 is attached to the EGR pipe 15. The EGR control valve 16 is a linear electromagnetic valve, and its valve lift varies linearly in response to a drive signal from the ECU 2, thereby opening and closing the EGR pipe 15. The ECU 2 controls the EGR amount by controlling the valve lift amount of the EGR control valve 16 according to the operating state of the engine 3.

  The exhaust pipe 14 is provided with a catalyst device 17. The catalyst device 17 is a combination of a three-way catalyst and a NOx adsorption catalyst. This NOx adsorption catalyst is obtained by coating the surface of a honeycomb-structured base material with an iridium catalyst (iridium-supported silicon carbide whisker powder and silica), and further firing a perovskite type double oxide (LaCoO3 powder and silica). Body) is further coated. The catalyst device 17 purifies CO, HC and NOx in the exhaust gas during operation by the oxidation-reduction action of the three-way catalyst, and operates in the stratified combustion mode described later by the adsorption action and reduction action by the NOx adsorption catalyst. NOx in the exhaust gas at the time and during lean burn operation is purified.

  Further, a LAF sensor 28 and an O 2 sensor (not shown) are provided on the upstream side and the downstream side of the exhaust pipe 14 from the catalyst device 17, respectively. The LAF sensor 28 is composed of zirconia and a platinum electrode, etc., and linearly detects the oxygen concentration in the exhaust gas in a wide range of air-fuel ratios from a rich region richer than the theoretical air-fuel ratio to an extremely lean region. Is output to the ECU 2. The ECU 2 calculates a detected air-fuel ratio KACT representing the air-fuel ratio in the exhaust gas based on the detection signal of the LAF sensor 28. The detected air-fuel ratio KACT is specifically calculated as an equivalence ratio. On the other hand, the O2 sensor outputs a detection signal indicating the oxygen concentration in the exhaust gas to the ECU 2.

  Furthermore, an atmospheric pressure sensor 29, an accelerator opening sensor 30, and a vehicle speed sensor 31 are electrically connected to the ECU 2. The atmospheric pressure sensor 29 is composed of a semiconductor pressure sensor, detects the atmospheric pressure PA, and outputs a detection signal to the ECU 2. The accelerator opening sensor 30 detects an accelerator opening AP, which is an operation amount of an accelerator pedal (not shown), and outputs a detection signal to the ECU 2. Further, the vehicle speed sensor 31 detects a vehicle speed (hereinafter referred to as “vehicle speed”) VP (not shown) and outputs a detection signal to the ECU 2.

  In the present embodiment, the ECU 2 includes an operating state detecting means, a required torque calculating means, a combustion mode determining means, a transition time fuel injection amount calculating means, an intake stroke fuel injection amount calculating means, and a double fuel injection ending means according to the present invention. , And a rotational speed detection means, and is composed of a microcomputer including a CPU 2a, a RAM 2b, a ROM 2c, and the like. The ECU 2 executes various arithmetic processes based on the control programs stored in the ROM 2c according to the detection signals of the various sensors 20 to 31 described above.

  Specifically, the operating state of the engine 3 is determined from the above various detection signals, and based on the determination result, the combustion mode of the engine 3 is changed to the stratified combustion mode at the time of extremely low load operation, and other than at the time of extremely low load operation. During the operation of the engine, the mode is switched to the uniform combustion mode, and in the state during the transition from one of the uniform combustion mode and the stratified combustion mode to the other (hereinafter referred to as “combustion transition mode”), in principle, the two-injection combustion mode (2 times fuel injection) is executed. Further, by controlling the final fuel injection amount TOUT and the injection timing of the injector 4 according to the combustion mode, the fuel injection control process is executed and the ignition timing of the spark plug 5 and the like are controlled.

  In the stratified combustion mode, fuel is injected from the injector 4 into the combustion chamber 3c during the compression stroke, and a fuel jet is formed by causing most of the injected fuel to collide with the recess 3d. An air-fuel mixture is generated by this fuel jet and the flow of the inflow air from the intake pipe 12, and the piston 3a is located near the top dead center of the compression stroke, so that the air-fuel mixture is brought close to the spark plug 5. Stratified combustion is performed while being unevenly distributed. Further, the air-fuel ratio of the air-fuel mixture in the stratified combustion mode is controlled to an air-fuel ratio (for example, 27 to 60) that is much leaner than the stoichiometric air-fuel ratio by controlling the throttle valve 13a to be in a fully open state.

  In the uniform combustion mode, fuel is injected into the combustion chamber 3c during the intake stroke, and uniform combustion is performed while an air-fuel mixture generated by the fuel jet and air flow is uniformly dispersed in the combustion chamber 3c. In addition, the air-fuel ratio in the uniform combustion mode is richer than that in the stratified combustion mode by reducing the intake air amount by controlling the throttle valve 13a to a small opening as compared with that in the stratified combustion mode. The air-fuel ratio is controlled (for example, 12 to 22). Further, the target valve lift amount of the EGR control valve 16 in the uniform combustion mode is set to a smaller value than in the stratified combustion mode.

  Further, in the double injection combustion mode, fuel is injected during the intake stroke and the compression stroke in one combustion cycle, and combustion is performed at a richer air-fuel ratio (for example, 14.7 to 27) than in the stratified combustion mode. Is called.

  The uniform combustion mode is divided into a stoichiometric combustion mode and a lean combustion mode. In the stoichiometric combustion mode, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio or richer than this, and in the lean combustion mode, the air-fuel ratio is controlled to be leaner than in the stoichiometric combustion mode.

  Next, a fuel injection control process including an air-fuel ratio feedback control process executed by the ECU 2 will be described with reference to FIGS. FIG. 2 shows the main routine of this control process. This process is interrupted in synchronization with the input of the TDC signal. In this process, first, in step 1 (illustrated as “S1”, the same applies hereinafter), the required torque PMCMD is calculated by searching the map shown in FIG. 14 according to the engine speed NE and the accelerator pedal opening AP. In this map, the required torque PMCMD is set to a larger value as the engine speed NE is higher and the accelerator pedal opening AP is larger. This is because the engine load becomes larger as the engine speed NE is higher and the accelerator pedal opening AP is larger, and this is to cope with it. This required torque PMCMD is the indicated mean effective pressure at the time of air-fuel mixture combustion.

  Next, the routine proceeds to step 2 where the stratified combustion permission flag F_DISCOK is set. This stratified combustion permission flag F_DISCOK indicates whether the engine 3 is in an operation state in which the stratified combustion mode or the uniform combustion mode is to be executed, and according to the required torque PMCMD and the engine speed NE, FIG. This is set by searching the map shown in FIG. Specifically, in this map, in the stratified combustion region where both the required torque PMCMD and the engine speed NE are low, the stratified combustion permission flag F_DISCOK is set to “1”, assuming that the engine 3 is in an operating state in which the stratified combustion mode should be executed. Set to On the other hand, in the uniform combustion region where the required torque PMCMD and the engine speed NE are higher than those in the stratified combustion region, specifically, in the lean combustion region and the stoichiometric combustion region, the engine 3 is in the lean combustion mode and the stoichiometric combustion in the uniform combustion mode. The stratified combustion permission flag F_DISCOK is set to “0”, assuming that the operation state is to execute the mode. The stoichiometric combustion region in this map is set to include a rich region in which the air-fuel mixture is burned at an air-fuel ratio richer than the stoichiometric air-fuel ratio in addition to a region in which the air-fuel mixture is burned mainly at the stoichiometric air-fuel ratio. .

  Next, the process proceeds to step 3, and various correction coefficients used in various calculation processes to be described later are calculated in accordance with, for example, the elapsed start time of the engine 3, the vehicle speed VP, the intake air temperature TA, the atmospheric pressure PA, or the engine water temperature TW. .

  Next, in step 4, a target air-fuel ratio KCMD1ST for intake stroke injection and a target air-fuel ratio KCMD2ND for compression stroke injection are calculated. When the combustion mode is the uniform combustion mode, the former is used, while when the combustion mode is the stratified combustion mode, the latter is used. When the combustion mode is the combustion transition mode, one of KCMD1ST and KCMD2ND is appropriately used. The target air-fuel ratios KCMD1ST and KCMD2ND are calculated according to the engine speed NE, the required torque PMCMD, and the like.

  Next, the routine proceeds to step 5 where an air-fuel ratio feedback correction coefficient KAF is calculated. The air-fuel ratio feedback correction coefficient KAF is calculated according to the combustion mode. Specifically, the detected air-fuel ratio KACT, the target air-fuel ratio KCMD1ST for intake stroke injection, or the target air-fuel ratio for compression stroke injection It is calculated by a predetermined feedback control algorithm according to KCMD2ND or the like.

  Next, in steps 6 and 7, a basic fuel injection amount TIM1ST for intake stroke injection and a basic fuel injection amount TIM2ND for compression stroke injection are calculated, respectively. Specifically, in calculating the basic fuel injection amount TIM1ST for intake stroke injection, first, the actual intake air amount GCYL (the air amount estimated to be actually sucked into the cylinder 10) is converted into the TH passing intake air amount GTH and It is calculated according to the intake pipe absolute pressure PBA. Then, by searching a basic fuel injection amount table (not shown) according to the actual intake air amount GCYL, the table value is calculated and corrected, thereby correcting the basic fuel injection amount TIM1ST for intake stroke injection. Is calculated. Similarly to the above, the basic fuel injection amount TIM2ND for the compression stroke injection is also calculated.

  Next, the routine proceeds to step 8 where the required fuel injection amount TCYL is calculated. In calculating TCYL, first, as shown in FIG. 3, in step 11, a required fuel injection amount TCYL1STT (intake stroke fuel injection amount) for intake stroke injection is calculated. In the calculation of TCYL1STT, first, as shown in FIG. 4, a value obtained by multiplying the start time correction coefficient KAST, the deceleration time correction coefficient KDEC, and the acceleration time correction coefficient KACC among the various correction coefficients calculated in step 3 of FIG. The first total correction coefficient KTOTALTMP is set (step 21).

  The starting correction coefficient KAST is used to correct the increase in the fuel injection amount when starting the engine 3, and is calculated by searching a table (not shown) according to the elapsed time from the starting time. The deceleration correction coefficient KDEC is used to correct a decrease in the fuel injection amount when the vehicle is not shown, and searches a table (not shown) according to the deviation between the previous value and the current value of the vehicle speed VP. It is calculated by doing. Further, the acceleration correction coefficient KACC is used to correct the fuel injection amount when the vehicle is accelerating, and searches a table (not shown) according to the deviation between the previous value and the current value of the vehicle speed VP. Is calculated by

  Next, the routine proceeds to step 22 where the value obtained by multiplying the intake temperature correction coefficient KTA, the atmospheric pressure correction coefficient KPA and the engine water temperature correction coefficient KTW among the various correction coefficients calculated in step 3 of FIG. 2 is set as the second total correction coefficient KTATWPA. Set as. These correction coefficients KTA, KPA, and KTW are calculated by searching respective tables (not shown) according to the intake air temperature TA, the atmospheric pressure PA, and the engine water temperature TW.

  Next, the process proceeds to step 23, and a value obtained by multiplying the first total correction coefficient KTOTALTMP and the second total correction coefficient KTATWPA set in steps 21 and 22 is set as the total correction coefficient KTTL1ST for intake stroke injection. The basic fuel injection amount TIM1ST for intake stroke injection calculated in step 6 of FIG. 2 is added to the air-fuel ratio feedback correction coefficient KAF calculated in steps 5 and 4 of FIG. 2 and the target air-fuel ratio KCMD1ST for intake stroke injection, respectively. In addition, by multiplying the intake stroke injection total correction coefficient KTTL1ST set in step 23, the required fuel injection amount TCYL1STT for intake stroke injection for each cylinder 10 is calculated (step 24), and this process is terminated.

  Returning to FIG. 3, in step 12, the required fuel injection amount TCYL2NDT for compression stroke injection is calculated. In the calculation of TCYL2NDT, first, as shown in FIG. 5, the value obtained by multiplying the correction coefficient KTA, the atmospheric pressure correction coefficient KPA, and the engine water temperature correction coefficient KTW among the correction coefficients calculated in Step 3 of FIG. The total correction coefficient KTTL2ND for compression stroke injection is set (step 31). The basic fuel injection amount TIM2ND for compression stroke injection calculated in step 7 of FIG. 2 is added to the air-fuel ratio feedback correction coefficient KAF and the target air-fuel ratio KCMD2ND for compression stroke injection calculated in steps 5 and 4 of FIG. In addition, by multiplying the total correction coefficient KTTL2ND for compression stroke injection set in step 31 above, the required fuel injection amount TCYL2NDT for compression stroke injection for each cylinder 10 is calculated, and this processing is terminated.

  Returning to FIG. 3, in step 13, the provisional required fuel injection amount TCYLLMT (transition fuel injection amount) is calculated. 6 and 7 show a process for calculating the temporary required fuel injection amount TCYLLMT. In this process, the provisional required fuel injection amount TCYLLMT is set to the required fuel injection amount TCYL1STT for intake stroke injection during the uniform combustion mode, and is set to the required fuel injection amount TCYL2NDT for compression stroke injection during the stratified combustion mode. On the other hand, during the combustion transition mode when switching between both combustion modes, it is set to one of first to fourth limit values TCYLDS, TCYLDL, TCYLSD, and TCYLLD, which will be described later.

  The reason why the required fuel amount at the time of switching different from the normal time is used when switching the combustion mode in this way is as follows. That is, as described above, the intake air amount that is set differs greatly between the stratified combustion mode and the uniform combustion mode, the stratified combustion mode is larger, and during the combustion transition mode when the combustion mode is switched, The amount of air changes with a response delay with respect to the operation of the throttle valve. On the other hand, the required fuel injection amounts TCYL1STT and TCYL2NDT for intake / compression stroke injection are set according to the intake air amount actually taken into the cylinder 10. For this reason, at the time of switching to the uniform combustion mode, the required fuel injection amount TCYL1STT for the intake stroke injection is likely to become excessive as a result of being set according to the intake air amount that decreases with a response delay. For the same reason, at the time of switching to the stratified combustion mode, the required fuel injection amount TCYL2NDT for compression stroke injection tends to be too small.

  The above-mentioned required fuel amount at the time of switching is limited to prevent the required fuel injection amount TCYL1STT / 2NDT from becoming excessively large or small until the intake air amount is stabilized during the combustion transition mode. Used for. For this reason, the first limit value TCYLDS applied when switching to the uniform combustion mode is set so as to limit the required fuel injection amount TCYL1STT for intake stroke injection on the upper limit side, while switching to the stratified combustion mode The third limit value TCYLSD or the like that is sometimes applied is set to limit the required fuel injection amount TCYL2NDT for compression stroke injection on the lower limit side. Hereinafter, such restriction by the required fuel amount at the time of switching such as the first limit value TCYLDS is referred to as “limit processing”.

First, in step 41 of FIG. 6, various parameters necessary for calculating the temporary required fuel injection amount TCYLLMT are calculated. Although not shown, in this calculation process, first, the required fuel injection amount TCYL1STT for the intake stroke injection in the uniform combustion mode and the required fuel injection for the compression stroke injection in the stratified combustion mode according to the stratified combustion permission flag F_DISCOK. The amount TCYL2NDT is set as the normal required fuel injection amount TCYLT, respectively. Further, the presence / absence of switching of the combustion mode and the switching pattern are determined, and the switching status EMOD_STS is set as follows according to the determination result.
(A) When switching from stratified combustion mode to stoichiometric combustion mode: “1”
(B) When switching from stratified combustion mode to lean combustion mode: “2”
(C) When switching from stoichiometric combustion mode to stratified combustion mode: “3”
(D) When switching from lean combustion mode to stratified combustion mode: “4”
(E) When other than (a) to (d): “0”

  Further, in this process, when the combustion transition mode is started, the provisional required fuel injection amount TCYLLMT obtained immediately before that is set as the required fuel injection amount TCYLMINI immediately before switching. Further, during the combustion transition mode, the amount of change in the required torque PMCMD from immediately before switching to the combustion mode is obtained, and the torque change correction term TCYLDPM is calculated by converting the obtained amount of change into a fuel amount.

  In step 42 following step 41, it is determined whether or not the required torque PMCMD is greater than zero. If the answer is NO and no torque is required for the engine 3, the timer value TTCYLMC of the elapsed time after switching of the up-counting type is set to a predetermined time TTCYLREF (for example, 5 sec) (step 43), and the temporary required fuel injection The amount TCYLLMT is set to the normal required fuel injection amount TCYLT (step 44). Further, the limit execution flag F_TCYLLMT is set to “0” (step 45), and limit processing is prohibited.

  On the other hand, if the answer to step 42 is YES and PMCMD> 0, it is determined whether or not the switching status EMOD_STS is “0” (step 46). When the answer is YES and the combustion mode is not switched, the steps 43 to 45 are executed. On the other hand, if the answer to step 46 is NO and EMOD_STS ≠ 0, it is determined whether or not the switching status EMOD_STS is equal to the previous value EMOD_STSZ (step 47). If the answer is YES and the switching status EMOD_STS has not changed and the current loop is not immediately after the start of the combustion transition mode, it is determined whether or not the limit execution flag F_TCYLLMT is “1” (step 49). When the answer is NO and the limit process is not executed, the steps 43 to 45 are executed. On the other hand, when the answer to step 49 is YES and limit processing is being executed, the process proceeds to step 50.

  On the other hand, when the answer to step 47 is NO and EMOD_STS is not equal to EMOD_STSZ, that is, when the current loop is immediately after the start of the combustion transition mode, the timer value TTCYLMC of the post-switching elapsed time timer set in step 43 is set to the value. Reset to 0 (step 48) and go to step 50.

  In this step 50, it is determined whether or not the timer value TTCYLMC of the elapsed time after switching is smaller than the limit time TMTCYLMT. The limit time TMTCYLMT is set under the same conditions as the setting of the switching status EMOD_STS, and a predetermined limit time is set for each of the combustion mode switching patterns (a) to (e). . If the answer to step 50 is YES, that is, if the limit time TMTCYLMT has not elapsed after the start of the combustion transition mode, it is determined whether or not the switching status EMOD_STS is “1” (step 51). If the answer is YES and the switching pattern is stratified combustion mode → stoichiometric combustion mode, the first limit value TCYLDS for this switching pattern is calculated (step 52). Next, the calculated first limit value TCYLDS is set as the provisional required fuel injection amount TCYLLMT (step 53), and the limit execution flag F_TCYLLMT is set to the value of the first limit value calculation flag F_TCYLDS (step 54).

  On the other hand, when the answer to step 51 is NO, steps 55 to 65 are executed in the same manner as steps 51 to 54 described above. First, in steps 55 and 59, it is determined whether or not the switching status EMOD_STS is “2” and “3”, respectively. When the answer to step 55 is YES (EMOD_STS = 2) and the switching pattern is stratified combustion mode → lean combustion mode, a second limit value TCYLDL for this switching pattern is calculated (step 56). The value TCYLDL is set as the temporary required fuel injection amount TCYLLMT (step 57), and the limit execution flag F_TCYLLMT is set to the value of the second limit value calculation flag F_TCYLDL (step 58).

  If the answer to step 59 is YES (EMOD_STS = 3) and the switching pattern is stoichiometric combustion mode → stratified combustion mode, a third limit value TCYLSD for this switching pattern is calculated (step 60). Limit value TCYLSD is set as provisional required fuel injection amount TCYLLMT (step 61), and limit execution flag F_TCYLLMT is set to the value of third limit value calculation flag F_TCYLSD (step 62). Further, when the answer to step 59 is NO (EMOD_STS = 4) and the switching pattern is the lean combustion mode → stratified combustion mode, a fourth limit value TCYLLD for this switching pattern is calculated (step 63). The limit value TCYLLD is set as the temporary required fuel injection amount TCYLLMT (step 64), and the limit execution flag F_TCYLLMT is set to the value of the fourth limit value calculation flag F_TCYLLD (step 65).

  On the other hand, when the answer to step 50 is NO and TTCYLMC ≧ TMTCYLMT, that is, when the limit time TMTCYLMT has elapsed after the start of the combustion transition mode, it is determined that the execution period of the limit process has ended, and the steps 44 and 45 are performed. Execute and finish the limit process.

  In Step 66 following Step 45, 54, 58, 62 or 65, it is determined whether or not the limit execution flag F_TCYLLMT is “1”. If the answer is YES and the limit process is being executed, it is determined whether or not the stratified combustion permission flag F_DISCOK is “0” (step 67). If the answer to this question is YES and the stratified charge combustion execution condition is not satisfied, the timer value TAFDTOS of the down-count delay timer is set to a predetermined standby time TMAFDTOS (for example, 3 sec) (step 68), and the routine proceeds to step 69. . On the other hand, when the answer to step 66 is NO and F_TCYLLMT = 0, or when the answer to step 67 is NO and F_DISCOK = 1, step 68 is skipped and the process proceeds to step 69.

  In step 69, it is determined whether or not the timer value TAFDTOS of the delay timer set in step 68 is 0. When this answer is NO, in order to prohibit the stratified combustion mode, the stratified combustion mode flag F_TAFDTOS0 is set to “0” (step 70), and this process is terminated. On the other hand, if the answer is YES and TAFDTOS = 0, the stratified combustion mode flag F_TAFDTOS0 is set to “1” (step 71), and this process is terminated.

  As apparent from steps 66 to 70, after the limit process is completed when the limit process is executed when switching from the stratified combustion mode to the uniform combustion mode, or after the execution condition of the stratified combustion is satisfied. The stratified charge combustion mode is prohibited until the waiting time TMAFDTOS elapses. Thereby, when switching from the stratified combustion mode to the uniform combustion mode, it is possible to prevent the combustion mode from immediately returning to the stratified combustion mode in accordance with the establishment of the stratified combustion execution condition or the end of the limit processing.

  Further, at the time of switching the combustion mode (step 46: NO), any one of the first to fourth limit values TCYLDS, TCYLDL, TCYLSD, and TCYLLD is performed according to the switching pattern at that time in steps 51 to 65. Is calculated. Specifically, the calculation processing (steps 52, 56, 60, 63) of these first to fourth limit values TCYLDS, TCYLDL, TCYLSD, and TCYLLD corresponds to the required fuel injection amount immediately before the start of the combustion transition mode. It is calculated according to the immediately preceding required fuel injection amount TCYLMMIN, the torque change correction term TCYLDPM corresponding to the change amount of the required torque PMCMD during the combustion transition mode, and the combustion efficiency parameter representing the combustion efficiency during the combustion transition mode. Then, the limit process is executed based on the calculated limit value, and when the limit time TMTCYLMT elapses during the combustion transition mode (step 50: NO), the limit process is terminated by steps 44 and 45.

  Returning to FIG. 3, in step 14, the required fuel injection amount TCYL3RD for the expansion stroke injection is calculated. In the calculation process of TCYL3RD, the required fuel injection amount to be injected during the expansion stroke in one combustion cycle is calculated. The reason why TCYL3RD is calculated and fuel is injected during the expansion stroke based on the TCYL3RD is as follows. That is, in the NOx adsorption catalyst that constitutes a part of the catalyst device 17, sulfur content is also adsorbed together with NOx in the exhaust gas. If the residual amount of sulfur content increases, the adsorption and reduction performance of the NOx adsorption catalyst will decrease. Therefore, by injecting fuel during the expansion stroke, the temperature of the NOx adsorption catalyst is raised and the exhaust gas is made rich in a reducing atmosphere, thereby desorbing the sulfur component adsorbed on the NOx adsorption catalyst, This is to release to the outside. Note that when the condition for injecting fuel is established during the expansion stroke, the expansion stroke injection flag F_DIBC is set to “1”.

Next, the routine proceeds to step 15 where a virtual target air-fuel ratio KCMDIMG is calculated. As shown in FIG. 8, in this KCMDIMG calculation process, the target air-fuel ratio KCMD1ST for intake stroke injection calculated in step 4 of FIG. 2, the temporary required fuel injection amount TCYLLMT calculated in step 13 of FIG. 3, and FIG. Using the required fuel injection amount TCYL1STT for intake stroke injection calculated in step 11 of (1) below, the calculation is performed by the following equation (1) (step 81), and this processing is terminated.
KCMDIMG = KCMD1ST · TCYLLMT / TCYL1STT (1)

  This virtual target air-fuel ratio KCMDIMG is a value obtained by multiplying the target air-fuel ratio KCMD1ST for intake stroke injection used in the uniform combustion mode by TCYLLMT / TCYL1STT, and is used in the setting process of the combustion transition mode flag F_DSCMOD described later. is there.

  Returning to FIG. 3, in step 16, it is determined whether or not the stratified charge permission flag F_DISCOK is “1”. If the answer is YES and the engine 3 is in the operating state in which the stratified combustion mode is to be executed, the required fuel amount TCYL is set to the provisional required fuel injection amount TCYLLMT calculated in step 13 (step 17), and this process is performed. finish. On the other hand, when the answer to step 16 is NO, the process proceeds to step 18 to determine whether or not the expansion stroke injection flag F_DIBC is “1”. When the answer is YES, it is assumed that the condition for injecting fuel during the expansion stroke in one combustion cycle is satisfied, and the required fuel injection for the expansion stroke injection calculated in step 14 is calculated as the provisional required fuel injection amount TCYLLMT. A value obtained by adding the amount TCYL3RD is set as the required fuel amount TCYL (step 19), and this process is terminated. On the other hand, when the answer to step 18 is NO, the above step 17 is executed and the present process is terminated.

  Returning to FIG. 2, in step 9, the final fuel injection amount TOUT is calculated. The final fuel injection amount TOUT is calculated by correcting the required fuel injection amount TCYL calculated in step 8 according to the fuel pressure PF and the fuel temperature TF.

  Next, the routine proceeds to step 10, where fuel injection is executed based on the final fuel injection amount TOUT calculated in step 9, and this processing is terminated. FIG. 9 shows the execution process of this fuel injection. As shown in the figure, in this fuel injection, first, a combustion transition mode flag F_DSCMOD is set (step 91). In this setting process, as shown in FIG. 10, it is first determined in step 101 whether or not the fuel cut flag F_FC is “1”. This F_FC is a flag that is set to “1” when the engine 3 is in the fuel cut operation. When the answer to step 101 is YES and the fuel cut operation is in progress, the timer of the combustion transition mode execution timer is set. The value TMDSCMOD is set to 0 (step 102), and the combustion transition mode flag F_DSCMOD is set to “0” (step 103) to indicate that the combustion transition mode is not in effect (step 103), and this process is terminated.

  On the other hand, when the answer to step 101 is NO and the fuel cut operation is not being performed, it is determined whether or not the combustion transition mode flag F_DSCMOD stored in the RAM 2b is “1” (step 104). If this answer is NO, it is determined that the combustion transition mode is not being executed, and the routine proceeds to step 105, where it is determined whether or not the current value F_DISCOK of the stratified combustion permission flag is the same as the previous value F_DISCOKZ. When this answer is YES, it is determined that the engine 3 is not in an operation state in which the combustion mode should be switched, and the above steps 102 and 103 are executed, and this process is terminated. On the other hand, if the answer to step 105 is NO and F_DISCOKZ ≠ F_DISCOK, it is determined that the engine 3 is in an operation state in which the combustion mode should be switched, and the process proceeds to step 106.

  In this step 106, it is determined whether or not the stratified combustion permission flag F_DISCOK is “1”. When this answer is YES, that is, when the present combustion mode switching pattern is the uniform combustion mode → stratified combustion mode, the routine proceeds to step 107 in FIG.

  In step 107, it is determined whether or not the target air-fuel ratio KCMD1ST for intake stroke injection calculated in step 4 of FIG. 2 is equal to or greater than a predetermined value KCMDDSCMD (for example, 0.85). When this answer is NO and KCMD1ST <KCMDDSCMD, it is determined that the combustion mode switching pattern is the lean combustion mode → the stratified combustion mode, and the timer value TMDSCMOD of the down-count type combustion transition mode execution timer is set to the first timer value. TMDSCMLD is set (step 108), and the process proceeds to step 109 described later. On the other hand, when the answer to step 107 is YES and KCMD1ST ≧ KCMDDSCMD, it is determined that the current combustion mode switching pattern is stoichiometric combustion mode → stratified combustion mode, and the process proceeds to step 110.

  In this step 110, it is determined whether or not the engine state determination value NKENGCMD is “1”. The engine state determination value NKENGCMD is set according to the operation state when the engine 3 is in an operation state in which the combustion mode should be switched. Specifically, when the engine 3 is in an idle operation, It is set to “1”, “2” when operating under a high load, and “3” when operating under a low load.

  Therefore, when the answer to step 110 is YES and NKENGCMD = 1, the timer value TMDSCMOD of the combustion transition mode execution timer is set to the second timer value TMDSCMDD (step 111), the answer to step 110 is NO, and NKENGCMD = 2 (Step 112: YES), the timer value TMDSCMOD of the combustion transition mode execution timer is set to the third timer value TMDSCMSD2 (step 113). When the answer to step 112 is NO and NKENGCMD = 3, the combustion transition mode is executed. The timer value TMDSCMOD of the timer is set to the fourth timer value TMDSCMSD3 (step 114).

  In Step 109 following Step 108, 111, 113 or 114, the uniform combustion switching flag F_DSCMDS is set to “0” to indicate that the current combustion mode switching pattern is not the stratified combustion mode → the uniform combustion mode. set.

  Next, the routine proceeds to step 115, where it is determined whether or not the timer value TMDSCMOD of the combustion transition mode execution timer is 0. If the answer is NO and the combustion transition mode is in effect, the combustion transition mode flag F_DSCMOD is set to “1” to indicate that (step 116), and the present process is terminated. On the other hand, when the answer to step 115 is YES and the timer value TMDSCMOD of the combustion transition mode execution timer is 0, the combustion transition mode flag F_DSCMOD is set to “0” to indicate that it is not in the combustion transition mode. Set (step 117), the process is terminated.

  When the answer to step 106 is NO and F_DISCOK = 1, it is determined that the current combustion mode switching pattern is the stratified combustion mode → the uniform combustion mode, and the timer value TMDSCMIN of the down-count type combustion transition mode continuation timer is set to a predetermined value. Time TMDSCMDS1 (for example, 0.5 sec) is set (step 118). This predetermined time TMDSCMDS1 is set according to a value representing the responsiveness of the EGR control valve 16. For example, when the EGR control valve 16 is closed to compensate for the response delay of the EGR control valve 16, the predetermined time TMDSCMDS1 is set. It is set as the closing time required for the actual valve lift to change from 100% to 5%.

  In steps 119 and 120 following step 118, the uniform combustion switching flag F_DSCMDS is used to indicate that the current combustion mode switching pattern is the stratified combustion mode → the uniform combustion mode and that the combustion transition mode is being performed. And the combustion transition mode flag F_DSCMOD are both set to “1”, and this process is terminated.

  In step 120 or step 116, the combustion transition mode flag F_DSCMOD is set to “1”, so that the answer to step 104 becomes YES in the next loop, and the process proceeds to step 121 at that time. In step 121, it is determined whether or not the uniform combustion switching flag F_DSCMDS set in step 119 or 109 is “1”. If the answer is YES and the current combustion mode switching pattern is stratified combustion mode → uniform combustion mode, the routine proceeds to step 123.

  In step 123, it is determined whether or not the timer value TMDSCMIN of the combustion transition mode continuation timer is 0. When this answer is NO, it is assumed that the combustion transition mode at the time of switching to the uniform combustion mode should be continued, and this process is terminated as it is. On the other hand, when the answer to step 123 is YES and TMDSCMIN = 0, when the combustion injection in the combustion transition mode, that is, the fuel injection in the double injection combustion mode is continuously executed for a predetermined time TMDSCMDS1, the process proceeds to step 124. It is determined whether or not the virtual target air-fuel ratio KCMDIMG calculated in step 15 in FIG. 3 is larger than a combustion transition mode end determination value KCMDDSC (for example, 0.7 (a value corresponding to air-fuel ratio 21)).

  When the answer to step 124 is NO and KCMDIMG ≦ KCMDDSC, the air-fuel ratio in the combustion transition mode indicates a lean value with respect to a value suitable for the uniform combustion mode, and the combustion transition mode should be continued. If there is, the process is terminated. On the other hand, when the answer to step 124 is YES and KCMDIMG> KCMDDSC, the air-fuel ratio becomes a value suitable for execution of the uniform combustion mode, the combustion transition mode should be terminated, and the uniform combustion mode should be executed. Steps 102 and 103 are executed, and this process ends.

  The reason why the end of the combustion transition mode is determined is as follows. That is, as described above, the intake air amount that is set is greatly different between the stratified combustion mode and the uniform combustion mode, the stratified combustion mode is larger, and when the combustion mode is switched, the intake air amount is determined by the throttle valve 13a. It changes with a response delay to the operation. On the other hand, the virtual target air-fuel ratio KCMDIMG is calculated by adding the temporary required fuel injection amount TCYLLMT and the intake stroke injection request to the target air-fuel ratio KCMD1ST for intake stroke injection used in the uniform combustion mode, as described in the equation (1). This is a value obtained by multiplying the ratio with the fuel injection amount TCYL1STT.

  This temporary required fuel injection amount TCYLLMT is set to the first limit value TCYLDS calculated in step 52 in FIG. 6 during the combustion transition mode when the switching pattern of the combustion mode is the stratified combustion mode → the stoichiometric combustion mode. During the combustion transition mode when the stratified combustion mode is changed to the lean combustion mode, the second limit value TCYLDL calculated in step 56 of FIG. 6 is set. On the other hand, since the required fuel injection amount TCYL1STT for intake stroke injection is set according to the intake air amount actually taken into the cylinder 10 as described above, the combustion transition mode when switching to the uniform combustion mode is set. Immediately after starting, the value is larger than the temporary required fuel injection amount TCYLLMT, decreases as the intake air amount decreases, and approaches the temporary required fuel injection amount TCYLLMT. Thus, the required fuel injection amount TCYL1STT for intake stroke injection approaches the provisional required fuel injection amount TCYLLMT, and as a result, the virtual target air-fuel ratio KCMDIMG is in the combustion transition mode when switching from the stratified combustion mode to the uniform combustion mode. Reflects the air / fuel ratio well. Therefore, using such a virtual target air-fuel ratio KCMDIMG, the air-fuel ratio is richer than in the stratified combustion mode, and the execution of the uniform combustion mode may be started, that is, the torque step does not occur and is uniform. It is possible to appropriately determine that stable combustion can be secured in the combustion mode.

  When the answer to step 121 is NO, that is, when the uniform combustion switching flag F_DSCMDS set in step 109 is “0”, the current combustion mode is switched from the uniform combustion mode to the stratified combustion mode. If there is, the routine proceeds to step 122, where it is determined whether or not the timer value TMDSCMOD of the combustion transition mode execution timer set at step 108, 111, 113 or 114 is 0. When this answer is NO, it is assumed that the combustion transition mode at the time of switching to the stratified combustion mode should be continued, and this processing is terminated as it is. On the other hand, when the answer to step 122 is YES, it is determined that the combustion transition mode should be ended and the switching to the stratified combustion mode should be completed, and the above steps 102 and 103 are executed, and this processing is ended.

  Returning to FIG. 9, in step 92, the double injection flag F_DBLINJ is set. In this F_DBLINJ setting process, as shown in FIG. 12, first, in step 131, it is determined whether or not the combustion transition mode flag F_DSCMOD set in step 91 of FIG. 9 is “1”. When this answer is NO and the combustion transition mode is not being executed, that is, when the current combustion mode is the stratified combustion mode or the uniform combustion mode, the routine proceeds to step 132, where it is determined whether or not the stratified combustion permission flag F_DISCOK is “1”. Determine. When the answer is YES and the current combustion mode is the stratified combustion mode, the intake stroke injection flag F_DIHC is set to “0” to indicate that fuel should be injected only during the compression stroke. Along with (Step 133), the compression stroke injection flag F_DISC is set to “1” (Step 134). Next, the routine proceeds to step 135, where it is assumed that the fuel should not be injected twice, in order to indicate that, the double injection flag F_DBLINJ is set to “0”, and this processing is terminated.

  On the other hand, when the answer to the above step 132 is NO and the current combustion mode is the uniform combustion mode, it is assumed that the fuel should be injected only during the intake stroke. Conversely, the intake stroke injection flag F_DIHC is set to “1” (step 136), and the compression stroke injection flag F_DISC is set to “0” (step 137), and the above step 135 is executed to complete the present process. To do.

  When the answer to step 131 is YES, that is, when the combustion transition mode is in progress, the routine proceeds to step 138, where the final fuel injection amount TOUT calculated in step 9 of FIG. The difference (TOUT−TIMDSC) from the fuel amount TIMDSC for the compression stroke injection, that is, the amount of fuel to be injected during the intake stroke at the time of the second fuel injection is from a predetermined injection possible lower limit value TOUTDIMIN (for example, 0.4 msec) It is also determined whether or not it is smaller. This injectable lower limit value TOUTDIMIN represents the minimum amount of fuel that can be injected by the injector 4. Further, the fuel amount TIMDSC for the compression stroke injection at the time of the second fuel injection is calculated by searching, for example, a TIMDSC table shown in FIG. 13 according to the engine speed NE. In this TIMDSC table, the fuel amount TIMDSC for compression stroke injection at the time of the second fuel injection is set so as to decrease as the engine speed NE increases. This is because the higher the engine speed NE, the easier the air-fuel mixture burns due to the in-cylinder flow, thereby reducing the minimum fuel injection amount that can be ignited in the compression stroke. In this TIMDSC table, the value of TIMDSC is set to be equal to or greater than the injectable lower limit value TOUTDIMIN of the injector 4.

  If the answer to step 138 is NO and TOUT−TIMDSC ≧ TOUTDIMIN, the fuel amount to be injected during the intake stroke during the second fuel injection in addition to the fuel amount TIMDSC for the compression stroke injection during the second fuel injection (TOUT-TIMDSC) can also be injected from the injector 4, and it is assumed that fuel should be injected during the intake stroke and the compression stroke, respectively. In order to indicate that, the intake stroke injection flag F_DIHC and the compression stroke injection flag F_DISC Are set to “1” (steps 139 and 140). Then, in order to indicate that the two-time fuel injection should be executed, the two-time injection flag F_DBLINJ is set to “1” (step 141), and this process ends.

  On the other hand, when the answer to step 138 is YES, that is, when the amount of fuel to be injected (TOUT-TIMDSC) is lower than the injectable lower limit value TOUTDIMIN during the intake stroke in the second fuel injection, that fuel amount cannot be injected, that is, When the fuel injection cannot be executed twice, the routine proceeds to step 142, where it is determined whether or not the stratified combustion permission flag F_DISCOK is “1”. When this answer is YES and the current combustion mode switching is the stratified combustion mode switching, that is, when the combustion mode before the start of the combustion transition mode (before the combustion mode switching) is the uniform combustion mode, the uniform combustion mode Similarly to the injection timing in the mode, the intake stroke injection flag F_DIHC is set to “1” to indicate that the fuel should be injected only during the intake stroke (step 143), and the compression stroke injection is performed. The flag F_DISC is set to “0” (step 144). Then, in this loop, it is assumed that fuel injection cannot be executed twice, and in order to express this, step 135 is executed, and this processing is terminated.

  On the other hand, when the answer to step 142 is NO, that is, when F_DISCOK = 0, the current combustion mode is switched to the uniform combustion mode, and the combustion mode before the start of the combustion transition mode is the stratified combustion mode. Like the injection timing in the stratified combustion mode, the intake stroke injection flag F_DIHC is set to “0” to indicate that the fuel should be injected only during the compression stroke (step 145), The compression stroke injection flag F_DISC is set to “1” (step 146), step 135 is executed, and this process is terminated.

  As described above, the fuel injection is executed at the injection timing as described above during the combustion transition mode for the following reason. That is, in the two-time fuel injection executed during the combustion transition mode when switching between the uniform combustion mode and the stratified combustion mode, the combustion is likely to become unstable, and therefore, in order to ensure the stability of the combustion, It is required that the fuel to be injected during the intake stroke and the compression stroke is injected in an appropriate amount. However, if the fuel to be injected during the intake stroke or the compression stroke when the fuel injection is performed twice is below the minimum fuel amount that can be injected by the injector 4, the fuel amount deviated from the original appropriate amount Thus, if fuel injection is executed twice, combustion becomes unstable. Such a situation where the fuel to be injected during the intake stroke or the compression stroke falls below the minimum fuel amount tends to occur particularly immediately after the start of the combustion transition mode. Therefore, when the above situation occurs, the final fuel injection amount TOUT is injected immediately before the start of the combustion transition mode, that is, at the injection timing of the combustion mode before switching, without executing the fuel injection twice. Thus, stable combustion can be ensured when switching the combustion mode.

  Returning to FIG. 9, in step 93 following step 92, it is determined whether or not the double injection flag F_DBLINJ set in step 92 is “1”. If the answer is YES and the two fuel injections are to be executed, the routine proceeds to step 94, where the two-time injection control is executed, and this process ends. As described above, in the two-time injection control, the final fuel injection amount TOUT is divided, and the fuel amount for the intake stroke injection (TOUT-TIMDSC) is injected during the intake stroke in one combustion cycle, and the compression stroke is being performed. The fuel amount TIMDSC for the compression stroke injection is injected into.

  On the other hand, when the answer to step 93 is NO, the process proceeds to step 95 to determine whether or not the intake stroke injection flag F_DIHC is “1”. If the answer is YES and the fuel should be injected during the intake stroke, the routine proceeds to step 96, where the intake stroke injection control is executed, and this processing is terminated. As described above, in this intake stroke injection control, the final fuel injection amount TOUT is injected only during the intake stroke within one combustion cycle. Although not shown, when the above-described expansion stroke injection flag F_DIBC is “1”, in the intake stroke injection control, the intake fuel amount obtained by subtracting the fuel amount TOUTB to be injected during the expansion stroke from the final fuel injection amount TOUT. While injecting during the stroke, the fuel amount TOUTB is injected during the expansion stroke.

  When the answer to step 95 is NO, the process proceeds to step 97 to determine whether or not the compression stroke injection flag F_DISC is “1”. If the answer is YES and the fuel should be injected during the compression stroke, the routine proceeds to step 98, where the compression stroke injection control is executed, and this processing is terminated. As described above, in this compression stroke injection control, the final fuel injection amount TOUT is injected only during the compression stroke within one combustion cycle. On the other hand, when the answer to step 97 is NO, that is, when all of steps 93, 95, and 97 are NO and the double injection flag F_DBLINJ, the intake stroke injection flag F_DIHC, and the compression stroke injection flag F_DISC are all “0”, Assuming that the fuel cut operation should be performed, the present process is terminated without executing the fuel injection.

  As described above in detail, according to the present embodiment, the temporary required fuel injection amount TCYLLMT and the required fuel injection amount TCYL1STT for intake stroke injection during the combustion transition mode at the time of switching from the stratified combustion mode to the uniform combustion mode. Based on the ratio, the virtual target air-fuel ratio KCMDIMG that well reflects the air-fuel ratio in the combustion transition mode is calculated, and this can be used to appropriately determine the end timing of the combustion transition mode. No fuel injection is performed, and therefore NOx emission can be minimized while ensuring good operability. In addition, during the combustion transition mode when switching to the uniform combustion mode, the two-injection combustion mode is continued for at least the predetermined time TMDSCMDS1, so that the effects of executing the two-time fuel injection, that is, stable combustion and suppression of torque steps are suppressed. Can be secured.

  Further, according to the present embodiment, when the fuel injection cannot be executed twice during the combustion transition mode due to the structure of the injector 4, the fuel mode before switching is not executed without executing the fuel injection twice. Since the final fuel injection amount TOUT is injected at the injection timing, stable combustion during the combustion transition mode can be ensured.

In addition, this invention can be implemented in various aspects, without being limited to the said embodiment described. In the embodiment, in order to determine the end timing of the combustion transition mode, the virtual target air-fuel ratio KCMDIMG calculated based on the ratio between the temporary required fuel injection amount TCYLLMT and the required fuel injection amount TCYL1STT for intake stroke injection, and combustion The transition mode end determination value KCMDDSC was compared. As the determination value, a value obtained by dividing the combustion transition mode firing end determination value KCMDDSC by the target air-fuel ratio KCMD1ST for intake stroke injection (KCMDDSC / KCMD1ST) is adopted. And TCYLLMT / TCYL1STT,
TCYLLMT / TCYL1STT> KCMDDSCMD / KCMD1ST
At this time, the combustion transition mode may be terminated. Further, instead of the ratio between the temporary required fuel injection amount TCYLLMT and the required fuel injection amount TCYL1STT for intake stroke injection, a value calculated based on the deviation between the two (TCYLLMT-TCYL1STT) or the like is used to make an appropriate determination. The combustion transition mode may be terminated by comparing with the value.

  Further, in the embodiment, the fuel injection during the two-injection combustion mode, that is, whether or not the two-time fuel injection is performed, determines whether or not the fuel amount to be injected during the intake stroke (TOUT−TIMDSC) and the lower limit value TOUTDIMIN that can be injected by the injector 4. (Step 138), for example, if the fuel amount TIMDSC for compression stroke injection may be lower than the injectable lower limit value TOUTDIMIN, it is determined twice based on the comparison result between the two. Whether or not fuel injection can be executed may be determined. Further, instead of the injectable lower limit value TOUTDIMIN, an appropriate value larger than this can be adopted. In addition, it is possible to appropriately change the detailed configuration within the scope of the gist of the present invention.

Explanation of symbols

1 Control device
2 ECU (operating state detection means, required torque calculation means,
Combustion mode determining means, fuel injection amount calculating means for transition,
Fuel injection amount calculating means for intake stroke, means for terminating fuel injection,
And rotation speed detection means)
3 Internal combustion engine
10 cylinders
13 Throttle valve mechanism (operating state detection means)
15 EGR pipe (ERG flow path)
16 EGR control valve (EGR valve)
22 Crank angle sensor (operating state detection means, rotation speed detection means)
24 Air flow sensor (intake air amount detection means)
25 Throttle valve opening sensor (operating state detection means)
26 Intake pipe absolute pressure sensor (operating state detection means)
30 accelerator opening sensor (operating state detection means)
PMCMD required torque TCYL1STT required fuel injection amount for intake stroke injection (fuel injection amount for intake stroke)
TCYLLMT provisional required fuel injection amount (fuel injection amount for transition)
KCMDIMG Virtual target air-fuel ratio TMDSCMDS1 Predetermined time

Claims (5)

The combustion mode is switched between a uniform combustion mode in which fuel injection into the cylinder is performed during the intake stroke and a stratified combustion mode in which fuel injection is performed during the compression stroke, and the uniform combustion mode and the stratified combustion mode are And a control device for an in-cylinder injection type internal combustion engine that performs fuel injection twice to inject fuel during an intake stroke and during a compression stroke in one combustion cycle during transition during switching of the combustion mode between And
An operating state detecting means for detecting an operating state of the internal combustion engine;
Requested torque calculating means for calculating the required torque of the internal combustion engine according to the detected operating state of the internal combustion engine;
Combustion mode determining means for determining the combustion mode as one of the uniform combustion mode and the stratified combustion mode according to the calculated required torque;
A transition time fuel injection amount calculating means for calculating a transition time fuel injection amount to be injected during the transition in accordance with the calculated required torque;
An intake air amount detecting means for detecting an intake air amount;
An intake stroke fuel injection amount calculating means for calculating an intake stroke fuel injection amount to be injected during the intake stroke according to the detected intake air amount;
During the second fuel injection at the time of switching from the stratified combustion mode to the uniform combustion mode, the two-time fuel injection is performed according to a comparison result between the fuel injection amount for the transition time and the fuel injection amount for the intake stroke. A two-time fuel injection end means for ending
A control device for an internal combustion engine, comprising:   The two-time fuel injection end means ends the second-time fuel injection when a ratio between the transition time fuel injection amount and the intake stroke fuel injection amount is larger than a predetermined value. The control device for an internal combustion engine according to claim 1. The operating state detection means has a rotation speed detection means for detecting the rotation speed of the internal combustion engine,
3. The transition fuel injection amount calculating means calculates a fuel injection amount during a compression stroke of the second fuel injection according to the detected rotational speed of the internal combustion engine. The control apparatus of the internal combustion engine described in 1.   2. The two-time fuel injection end means compares the fuel injection amount for transition and the fuel injection amount for intake stroke after the second fuel injection is executed for a predetermined time. The control device for an internal combustion engine according to any one of claims 1 to 3. The internal combustion engine includes an EGR passage for recirculating exhaust gas to the intake side of the internal combustion engine;
And an EGR valve that opens and closes the EGR passage,
The control apparatus for an internal combustion engine according to claim 4, wherein the predetermined time is set according to responsiveness of the EGR valve.

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