JP3982626B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an in-cylinder internal combustion engine that operates by switching a combustion mode between a stratified combustion mode and a uniform combustion mode and controls a fuel injection amount in accordance with a calculated required fuel amount.

  Conventionally, what was disclosed by patent document 1, for example is known as this kind of control apparatus. In this control device, when the combustion mode of the internal combustion engine mounted on the vehicle is switched from the stratified combustion mode to the uniform combustion mode, stratified combustion is continuously performed for some of the plurality of cylinders. In this case, the fuel injection amount of some of the cylinders includes the previous fuel injection amount, the ratio between the current value of the torque correction amount set based on the rotational speed of the internal combustion engine and the previous value, and the basic fuel injection amount. Is set to a value obtained by multiplying the ratio between the current value and the previous value. More specifically, the torque correction amount is set as a value that is increased or decreased by a fixed amount according to the increase or decrease between the previous value and the current value of the rotational speed of the internal combustion engine. The basic fuel injection amount is set to a value obtained by weighted averaging the previous value and the current fuel injection amount calculated based on the intake air amount and the rotational speed of the internal combustion engine. By calculating the fuel injection amount as described above, the fuel injection amount is controlled and the calculation load of the control device is reduced while reflecting the change in the rotational speed of the internal combustion engine and the intake air amount. .

  However, the conventional control device described above has the following problems. That is, in the fuel injection amount calculation method described above, when the combustion mode is switched, the fuel injection amount is based on the previous fuel injection amount, and the ratio between the previous value and the current value of the torque correction amount, and the basic fuel. It is set to a value obtained by multiplying the ratio between the previous value and the current value of the injection amount. This torque correction amount is only a value that is increased or decreased by a certain amount in accordance with the increase or decrease of the rotational speed of the internal combustion engine. Therefore, the ratio between the previous value and the current value is determined based on the change in the rotational speed of the internal combustion engine. Does not correctly reflect changes in engine torque. The basic fuel injection amount is a weighted average of the previous value and the current value of the basic fuel injection amount set according to the intake air amount and the rotational speed of the internal combustion engine, that is, a smoothed value. Therefore, the ratio between the previous value and the current value also does not correctly reflect the change in torque based on the intake air amount and the rotational speed of the internal combustion engine. Therefore, the output torque of the internal combustion engine obtained from the fuel injection amount calculated based on these parameters does not necessarily match the required torque, resulting in a decrease in drivability.

  Further, as a control device for an in-cylinder injection internal combustion engine, the fuel injection amount is feedback-controlled so that the detected air-fuel ratio detected by the air-fuel ratio sensor becomes a target air-fuel ratio set according to the required torque or the like. There are also known ones. When such a control device is used in combination with the above-described conventional control device, there are the following problems. That is, since the target air-fuel ratio that is set differs greatly between the stratified combustion mode and the uniform combustion mode, the target air-fuel ratio changes greatly when the combustion mode is switched, and the fuel injection amount is determined accordingly. In such a situation, when feedback control is executed, the fuel injection amount is controlled with a large control amount so as to compensate for a large deviation between the target air-fuel ratio and the detected air-fuel ratio. It is easy to fluctuate, and drivability also decreases.

  The present invention has been made in order to solve such problems. When the combustion mode is switched, the output torque of the internal combustion engine can be made to coincide well with the required torque, and the output by feedback control of the air-fuel ratio can be achieved. It is an object of the present invention to provide a control device for an internal combustion engine that can suppress fluctuations in torque and rotational speed and thereby improve drivability.

Japanese Patent Laid-Open No. 11-50895

In order to achieve the above object, the invention according to claim 1 is operated by switching the combustion mode between the stratified combustion mode in which the air-fuel mixture is stratified combustion and the uniform combustion mode in which uniform combustion is performed, and the required fuel amount (in the embodiment) A control device 1 for a direct injection internal combustion engine 3 that controls a fuel injection amount in accordance with a required fuel injection amount TCYL (hereinafter the same in this section), and an operating state for detecting an operating state of the internal combustion engine 3 Required fuel for calculating the required fuel amount according to the detection means (crank angle sensor 22, air flow sensor 24, intake pipe absolute pressure sensor 26, accelerator opening sensor 30, ECU 2) and the detected operating state of the internal combustion engine 3. Depending on the amount calculation means (ECU 2, step 7 in FIG. 2, steps 20 and 21 in FIG. 4, step 33 in FIG. 6, step 25 in FIG. 4) and the operating state of the internal combustion engine 3 The required torque calculation means (ECU 2, step 15 in FIG. 3) for calculating the required torque PMCMD of the internal combustion engine 3 and the required fuel amount (the required fuel injection amount TCYLMINI immediately before switching) calculated immediately before the combustion mode is switched. Storage means (ECU2, step 30 in FIG. 5) for storing, combustion efficiency estimation means (ECU2, step 70 in FIG. 7, FIG. 8) for estimating the combustion efficiency (combustion efficiency parameter KTCLLD) of the internal combustion engine 3, combustion mode Is switched as the required fuel amount (first limit value) according to the stored required fuel amount, the required torque calculated during the switching, and the combustion efficiency estimated during the switching. (TCYLDS, second limit value TCYLDL, third limit value TCYLSD, fourth limit value TCYLLD) The charge calculation means (ECU 2, steps 41, 46, 49, 52 in FIG. 5, steps 42, 47, 50, 53 in FIG. 6, step 25 in FIG. 4) and the air-fuel mixture burned in the internal combustion engine 3 Air-fuel ratio detection means (LAF sensor 28, ECU2) for detecting the fuel ratio (detected air-fuel ratio KACT), and target air-fuel ratio setting means (ECU2, FIG. 2) for setting the target air-fuel ratios KCMD1ST, KCMD2ND according to the required torque PMCMD Steps 2 and 3), feedback control means (ECU 2, step 4 in FIG. 2) for feedback control of the required fuel amount so that the detected air-fuel ratio becomes the set target air-fuel ratio KCMD1ST, KCMD2ND, and the combustion mode The feedback control by the feedback control means is prohibited when the required fuel amount at the time of switching is calculated. After the prohibition by the first feedback control prohibiting means (ECU 2, steps 84 and 83 in FIG. 9) and the first feedback control prohibiting means, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 3 is detected by the air-fuel ratio detecting means. Feedback control restarting means (ECU 2, steps 94 to 99 in FIG. 9) for restarting feedback control at a predetermined timing (control start determination value TAFBDR) that is estimated to be possible is provided.

  According to the control device for an internal combustion engine, the required fuel amount calculation means calculates the required fuel amount in each combustion mode according to the operating state of the internal combustion engine, and the fuel injection amount is determined according to the calculated required fuel amount. Be controlled. When the combustion mode is switched, the required fuel amount for switching is calculated as the required fuel amount by the required fuel amount calculating means for switching. This is due to the following reason. That is, in general, in the stratified combustion mode, the intake air amount is very large and combustion is performed at an extremely lean air-fuel ratio, whereas in the uniform combustion mode, the intake air amount is smaller than that in the stratified combustion mode and a richer air-fuel ratio is achieved. Combustion takes place. Further, when the combustion mode is switched, the intake air amount does not change immediately, but with a response delay, it takes time to converge to a value suitable for the switched combustion mode. In such a situation, when the required fuel amount is calculated according to the operating state such as the intake air amount when switching the combustion mode, the required fuel amount fluctuates rapidly, and the output torque of the internal combustion engine does not easily match the required torque. Therefore, in order to avoid such a situation, the required fuel amount is limited.

  Further, according to the present invention, the required torque of the internal combustion engine is calculated according to the operating state of the internal combustion engine by the required torque calculation means, and the combustion efficiency of the internal combustion engine is estimated by the combustion efficiency estimation means. The above-mentioned required fuel amount at the time of switching is calculated according to the required fuel amount calculated immediately before switching of the combustion mode, the required torque calculated during switching, and the combustion efficiency estimated during switching.

  Thus, since the required fuel amount at the time of switching is calculated based on the required fuel amount immediately before the switching of the combustion mode, the transition of the combustion mode can be performed smoothly without causing a steep step in torque before and after the switching. it can. Further, since the required fuel amount at the time of switching is calculated according to the required torque calculated during the switching of the combustion mode, the change amount of the actual required torque from immediately before the switching of the combustion mode to the time point is reflected well. The required fuel amount at the time of switching can be set appropriately. Furthermore, since the combustion efficiency differs between the stratified combustion mode and the uniform combustion mode, the combustion efficiency changes at the time of switching, whereas the above-described configuration calculates the required fuel amount at switching according to the combustion efficiency during switching. Therefore, this can be appropriately set according to the actual combustion efficiency at that time. As described above, at the time of switching the combustion mode, the output torque of the internal combustion engine can be made to agree well with the required torque, thereby improving drivability.

Further, according to the present invention, the required fuel amount is feedback controlled so that the detected air-fuel ratio becomes the set target air-fuel ratio, the combustion mode is switched, and the required fuel amount at the time of switching is calculated. The feedback control is prohibited by the first feedback control prohibiting means. As described above, when the required fuel amount is limited by the required fuel amount at the time of switching in accordance with the switching of the combustion mode, the feedback control of the required fuel amount according to the target air-fuel ratio and the detected air-fuel ratio is prohibited. Therefore, even when the target air-fuel ratio changes greatly at the time of switching the combustion mode, and the deviation between the target air-fuel ratio and the detected air-fuel ratio increases accordingly, fluctuations in the required fuel amount due to feedback control corresponding thereto can be avoided. . Thereby, fluctuations in the output torque and rotation speed of the internal combustion engine at the time of switching the combustion mode can be suppressed, and therefore drivability can be improved.
Further, after the prohibition by the first feedback control prohibiting means, the feedback control is resumed at a predetermined timing that is estimated that the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine can be detected by the air-fuel ratio detecting means.

According to a second aspect of the present invention, in the control device for an internal combustion engine according to the first aspect, the feedback control is prohibited when the fuel cut for stopping the fuel supply to the internal combustion engine 3 is executed. 2 further includes feedback control prohibiting means (ECU 2, steps 87 and 83 in FIG. 9) , and the feedback control restarting means is after the prohibition by the first feedback control prohibiting means and after the prohibition by the second feedback control prohibiting means The predetermined timing is set to different timings (table values TMAFFBDT, TMAFFBD) (steps 94 , 95, 98 in FIG. 9).

According to this configuration, when the fuel cut is being executed, the feedback control is prohibited by the second feedback control prohibiting means. Further, after the prohibition of the feedback control, the predetermined timing to resume this, among the post-prohibited by the first and second feedback control inhibit means, are set to different times. For example, when the air-fuel ratio detection means is constituted by an air-fuel ratio sensor provided in the exhaust system, when the restriction by the required fuel amount at the time of switching is executed and when the fuel cut is executed, those executions are performed After the completion, a sufficient amount of exhaust gas reaches the air-fuel ratio sensor, and the timing at which the air-fuel ratio can be properly detected by the air-fuel ratio sensor is different. According to the present invention, since the timing of resuming the feedback control is set to a different timing between after the prohibition by the first and second feedback control prohibiting means, the feedback control is performed according to the previous prohibition cause. It is possible to start at the optimum timing, thereby improving the air-fuel ratio convergence by feedback control.

It is a figure showing roughly the control device by one embodiment of the present invention with an internal-combustion engine. It is a flowchart which shows the main routine of a fuel-injection control process. It is a flowchart which shows the calculation process of request | requirement torque PMCMD. FIG. 3 is a flowchart showing a calculation process of a required fuel injection amount TCYL in FIG. 2. FIG. FIG. 5 is a flowchart showing a process for calculating a provisional required fuel injection amount TCYLLMT in FIG. 4. It is a flowchart which shows the remaining part of the process of FIG. It is a flowchart which shows the calculation process of 4th limit value TCYLLD of FIG. It is a figure which shows an example of the KTCLLD table used by the process of FIG. It is a flowchart which shows the execution determination process of AF feedback control.

  Hereinafter, an internal combustion engine control apparatus according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the control device 1 includes an ECU 2, which performs a fuel injection control process for an internal combustion engine (hereinafter referred to as “engine”) 3 as described later.

  The engine 3 is, for example, a 4-cylinder (only one shown) type gasoline engine mounted on a vehicle (not shown). A combustion chamber 3c is formed between the piston 3a and the cylinder head 3b of each cylinder, and 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, a spark plug 5, an intake valve 8, and an exhaust valve 9 are attached to the cylinder head 3b so as to face the combustion chamber 3c. That is, the engine 3 is of a cylinder injection type in which fuel is directly injected into the combustion chamber 3c.

  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 to a high pressure from a fuel tank (not shown) by a high-pressure pump 4a, and is then regulated by a regulator (not shown), and then supplied to the injector 4, via the injector 4, It is injected toward the concave portion 3d side of the piston 3a. 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 fuel injected by the injector 4 collides with the recess 3d to form a fuel jet.

  Further, a fuel pressure sensor 20 is attached near the injector 4 of the fuel pipe 4b. The fuel pressure sensor 20 detects the fuel pressure PF of the fuel injected from the injector 4 and outputs a detection signal to the ECU 2. Further, the ECU 2 outputs a detection signal representing the fuel temperature (hereinafter referred to as “fuel temperature”) TF from the fuel temperature sensor 21. Further, as will be described later, the fuel injection time and the fuel injection timing (the valve opening timing and the valve closing timing) that are the valve opening time of the injector 4 are controlled by a drive signal from the ECU 2. The fuel injection time of the injector 4 corresponds to the amount of fuel injected into the cylinder, that is, the fuel injection amount, and is hereinafter referred to as “fuel injection amount”.

  Further, the spark plug 5 is discharged when a high voltage is applied from the ECU 2 at a timing corresponding to the ignition timing, whereby the air-fuel mixture in the combustion chamber 3c is combusted.

  The engine 3 is of the DOHC type, and includes an intake camshaft 6 and an exhaust camshaft 7 that open and close the intake valve 8 and the exhaust valve 9, respectively. Each of these camshafts 6 and 7 is connected to a crankshaft 3e via a timing belt (not shown), and rotates 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 and the MRE pickup 22b constitute a crank angle sensor 22 (operating state detecting means). The crank angle sensor 22 outputs a CRK signal and a TDC signal, which are pulse signals, with the rotation of the crankshaft 3e. The CRK signal is output every predetermined crank angle (for example, 30 °). The ECU 2 obtains the rotational speed NE (hereinafter referred to as “engine rotational speed”) NE of the engine 3 based on the CRK signal. The TDC signal is a signal indicating that the piston 3a of each cylinder is at a predetermined crank angle position near the TDC (top dead center) at the start of the intake stroke, and in this example of the 4-cylinder type, every crank angle of 180 °. One pulse is applied.

  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 or the like, detects an engine water temperature TW that is the temperature of cooling water circulating in the main body of the engine 3, and outputs a detection signal to the ECU 2. Further, in the intake pipe 12 of the engine 3, an air flow sensor 24 (operating state detecting means), a throttle valve mechanism 13, a throttle valve opening sensor 25, and an intake pipe absolute pressure sensor 26 (operating state detecting means) are sequentially arranged from the upstream side. Etc. are provided. The air flow sensor 24 is constituted by a hot-wire air flow meter or the like, detects the intake air amount GTH passing through the throttle valve 13a of the throttle valve mechanism 13, and outputs a detection signal to the ECU 2.

  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 intake air amount GTH changes according to the opening degree. The actuator 13b is a combination of a motor connected to the ECU 2 and a gear mechanism (both not shown). The actuator 13b is driven by a drive signal from the ECU 2, thereby opening the throttle valve 13a (hereinafter referred to as "throttle valve"). TH) changes.

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

  A catalyst device 17 is provided in the exhaust pipe 14 of the engine 3. This catalyst device 17 is a combination of a NOx catalyst and a three-way catalyst. This NOx catalyst is not shown, but an iridium catalyst (a sintered body of silicon carbide whisker powder carrying iridium and silica) is formed on a honeycomb structure. The surface of the material is coated, and a perovskite double oxide (LaCoO3 powder and silica fired body) is further coated thereon. The catalyst device 17 purifies NOx in the exhaust gas during the operation in the stratified combustion mode and the lean burn operation, which will be described later, by the reduction action of the NOx catalyst, and other than the lean burn operation by the oxidation reduction action of the three-way catalyst. During the operation, CO, HC and NOx in the exhaust gas are purified.

  Further, 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. Through the EGR pipe 15, the exhaust gas of the engine 3 is recirculated to the intake side, so that an EGR operation is performed to reduce NOx in the exhaust gas by lowering the combustion temperature in the combustion chamber 3c. The EGR pipe 15 is provided with an EGR control valve 16. The EGR control valve 16 is a linear electromagnetic valve, and the EGR pipe 15 is opened and closed when the valve lift amount changes linearly according to the drive signal from the re-ECU 2. The valve lift amount of the EGR control valve 16 is detected by a valve lift amount sensor (not shown), and the detection signal is output to the ECU 2.

  The ECU 2 calculates the target valve lift amount of the EGR control valve 16 according to the operating state of the engine 3 and controls the EGR control valve 16 so that the actual valve lift amount becomes the target valve lift amount. Control the EGR amount.

  Further, a LAF sensor 28 (air-fuel ratio detecting means) and an O2 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 stoichiometric air-fuel ratio to an extremely lean region. A detection signal 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. The O2 sensor outputs a detection signal indicating the oxygen concentration in the exhaust gas to the ECU 2.

  Further, an atmospheric pressure sensor 29, an accelerator opening sensor 30 (operating state detection means), and a shift position sensor 31 are 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 that is an operation amount of an accelerator pedal (not shown), and outputs a detection signal to the ECU 2. The shift position sensor 31 detects a shift position POSI of an automatic transmission (not shown) and outputs a detection signal to the ECU 2.

  In the present embodiment, the ECU 2 is, in this embodiment, operating state detection means, required fuel amount calculation means, required torque calculation means, storage means, combustion efficiency estimation means, switching required fuel amount calculation means, air-fuel ratio detection means, target air-fuel ratio setting means. The feedback control means, the first and second feedback control prohibiting means, and the start timing setting means are configured. The ECU 2 is composed of a microcomputer including a CPU 2a, a RAM 2b, a ROM 2c, and the like, and various arithmetic processings are performed based on control programs stored in the ROM 2c in accordance with the detection signals of the various sensors 20 to 32 described above. Execute. Specifically, the operating state of the engine 3 is determined from the various detection signals, and the combustion mode of the engine 3 is determined based on the determination result, and the fuel injection amount TOUT of the injector 4 is determined according to the determined combustion mode. The ignition timing of the spark plug 5 is controlled.

  The combustion mode is determined according to the engine speed NE and the required torque PMCMD calculated as described later. As a general rule, the combustion mode is determined to be the stratified combustion mode at the time of extremely low load operation such as idle operation, and the stratified combustion permission flag F_DISCOK is set to “1” accordingly. Further, the uniform combustion mode is determined during the operation other than during the extremely low load operation, and accordingly, the stratified combustion permission flag F_DISCOK is set to “0”. At the time of switching between both combustion modes, the combustion mode is determined to be the double injection combustion mode.

  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. This fuel jet and the flow of air flowing in from the intake pipe 12 generate an air-fuel mixture, and the piston 3a is located near the top dead center of the compression stroke, so that the air-fuel mixture is brought near 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 the air-fuel mixture generated by the flow of the fuel jet and air is uniformly dispersed in the combustion chamber 3c. In addition, the air-fuel ratio in the uniform combustion mode is controlled to be smaller than that in the stratified combustion mode, and the intake air amount is made smaller by controlling the throttle valve 13a so that the air-fuel ratio is richer than that in the stratified combustion mode (for example, 12-22). Further, the target valve lift amount of the EGR control valve 16 in the uniform combustion mode is set to a smaller value than that in the stratified combustion mode.

  Further, in the two-injection combustion mode, fuel is injected in each of 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.

  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, the fuel injection control process executed by the ECU 2 will be described with reference to FIGS. FIG. 2 shows a main routine of this fuel injection control process, and this process is executed in synchronization with the input of the TDC signal. In step 1 (illustrated as “S1”, the same applies hereinafter), various correction coefficients are calculated. Each of these correction coefficients is calculated by searching a table or a map (none of which is shown) according to various parameters such as the intake air temperature TA, the atmospheric pressure PA, and the engine water temperature TW.

  Next, in steps 2 and 3, a target air-fuel ratio KCMD1ST for intake stroke injection and a target air-fuel ratio KCMD2ND for compression stroke injection are calculated, respectively. The target air-fuel ratios KCMD1ST and KCMD2ND for intake / compression stroke injection are calculated according to the engine speed NE, the required torque PMCMD, and the like. This required torque PMCMD is calculated by the calculation process shown in FIG. 3. Specifically, in step 15, the required torque PMCMD is calculated by searching a map (not shown) according to the engine speed NE and the accelerator pedal opening AP. Is done. The required torque PMCMD is the indicated mean effective pressure during combustion of the air-fuel mixture.

  Next, the F / B correction coefficient KAF is calculated (step 4). The F / B correction coefficient KAF is calculated according to the combustion mode. Specifically, the detected air-fuel ratio KACT is detected based on the detected air-fuel ratio KACT detected by the LAF sensor 28 and the target air-fuel ratios KCMD1ST, KCMD2ND for intake / compression stroke injection obtained in steps 2 and 3 above. It is calculated by a predetermined feedback control algorithm so that the fuel ratio becomes KCMD1ST or KCMD2ND. Hereinafter, such feedback control of the air-fuel ratio based on the detection output of the LAF sensor 28 is referred to as “AF feedback control”. Further, when the execution condition of this AF feedback control is not satisfied, the F / B correction coefficient KAF is set to a predetermined value.

  Next, a basic fuel injection amount TIM1ST for intake stroke injection is calculated (step 5). The basic fuel injection amount TIM1ST is calculated as follows. That is, based on the intake air amount GTH, the intake pipe absolute pressure PBA, and the like, the actual intake air amount that is estimated to be actually taken into the cylinder is calculated. Then, a basic fuel injection amount TIM1ST for intake stroke injection is calculated by searching a table (not shown) according to the calculated actual intake air amount.

  Next, a basic fuel injection amount TIM2ND for compression stroke injection is calculated (step 6). The basic fuel injection amount TIM2ND is calculated in substantially the same manner as the basic fuel injection amount TIM1ST for intake stroke injection described above. A description of the calculation method is omitted.

  Next, a required fuel injection amount TCYL (required fuel amount) is calculated (step 7). This calculation process will be described later. Next, the final required fuel injection amount TOUT is calculated by correcting the calculated required fuel injection amount TCYL with the respective correction coefficients corresponding to the fuel pressure PF and the fuel temperature TF (step 8). Next, by outputting a drive signal based on the calculated fuel injection amount TOUT to the injector 4, fuel injection is executed (step 9), and this process ends. In the double injection combustion mode, the fuel injection amount TOUT is divided to obtain the fuel injection amount to be injected during the intake stroke and the compression stroke, and a drive signal based on the obtained fuel injection amount is output to the injector 4. Is done.

  Next, the required fuel injection amount TCYL calculation process executed in step 7 of FIG. 2 will be described with reference to the flowchart of FIG. First, at step 20, a required fuel injection amount TCYL1STT for intake stroke injection is calculated. This required fuel injection amount TCYL1STT is used as the required fuel injection amount TCYL in the uniform combustion mode. The required fuel injection amount TCYL1STT is obtained by calculating the various correction coefficients, the target air-fuel ratio KCMD1ST for intake stroke injection, the F / B correction coefficient KAF, and the basic fuel injection amount TIM1ST for intake stroke injection obtained in the processing of FIG. Calculated by multiplying each other.

  Next, a required fuel injection amount TCYL2NDT for compression stroke injection is calculated (step 21). This required fuel injection amount TCYL2NDT is used as the required fuel injection amount TCYL in the stratified combustion mode. The required fuel injection amount TCYL2NDT is calculated by multiplying various correction coefficients, a target air-fuel ratio KCMD2ND for compression stroke injection, an F / B correction coefficient KAF, and a basic fuel injection amount TIM2ND for compression stroke injection.

  Next, a temporary required fuel injection amount TCYLLMT is calculated (step 22). This calculation process will be described later. Next, a required fuel injection amount TCYL3RD for expansion stroke injection is calculated (step 23). In this expansion stroke injection, fuel is injected into the cylinder during the expansion stroke in order to recover the adsorption capacity of the catalyst device 17 by reducing and desorbing NOx and sulfur adsorbed on the catalyst device 17 respectively. is there. The description of the calculation method of the required fuel injection amount TCYL3RD is omitted.

  Next, it is determined whether or not the stratified combustion permission flag F_DISCOK is “1” (step 24). If the answer to step 24 is YES and the stratified combustion execution condition is satisfied, the provisional required fuel injection amount TCYLLMT calculated in step 22 is set as the required fuel injection amount TCYL (step 25). finish.

  On the other hand, if the answer to step 24 is NO and the stratified combustion execution condition is not satisfied, it is determined whether or not the expansion stroke injection flag F_DIBC is “1” (step 26). The expansion stroke injection flag F_DIBC is set to “1” when the above-described expansion stroke injection execution condition is satisfied.

  If the answer to step 26 is YES and the execution conditions for the expansion stroke injection are satisfied, the sum of the temporary required fuel injection amount TCYLLMT and the required fuel injection amount TCYL3RD for the expansion stroke injection is set as the required fuel injection amount TCYL. The setting is made (step 27), and this process ends. On the other hand, when the answer to step 26 is NO, the step 25 is executed, and this process is terminated.

  Next, the temporary required fuel injection amount TCYLLMT calculation process executed in step 22 will be described with reference to the flowcharts of FIGS. 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, when switching between the two combustion modes, it is set to one of first to fourth limit values TCYLDS, TCYLDL, TCYLSD, and TCYLLD (required fuel amount at switching) according to the switching pattern. Is done.

  The reason why the required fuel amount at the time of switching different from the normal time is used at the time of 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, and the stratified combustion mode is larger, and when the combustion mode is switched, the intake air amount depends on the operation of the throttle valve. Changes with a response delay. On the other hand, the required fuel injection amounts TCYL1STT and TCYL2NDT for intake / compression stroke injection are set according to the actual intake air amount actually taken into the cylinder. For this reason, at the time of switching to the uniform combustion mode, the required fuel injection amount TCYL1STT for 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, the required fuel injection amount TCYL2NDT for compression stroke injection tends to be too small when switching to the stratified combustion mode.

  The above-mentioned required fuel amount at the time of switching is to limit these in order to prevent the required fuel injection amount TCYL1STT / 2NDT from becoming too large or too small until the intake air amount becomes stable at the time of switching the combustion mode. Used for. Therefore, the first limit value TCYLDS or the like 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, the restriction of the required fuel injection amount by the first limit value TCYLDS or the like at the time of switching the combustion mode is referred to as “limit processing”.

  First, in step 30 of FIG. 5, 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 amount for the compression stroke injection in the stratified combustion mode according to the stratified combustion permission flag F_DISCOK. TCYL2NDT is set as the normal time required fuel injection amount TCYLT.

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) Other than (a) to (d): “0”

  In this process, when the combustion mode is switched, the provisional required fuel injection amount TCYLLMT obtained immediately before the combustion mode is set as the required fuel injection amount TCYLMINI immediately before switching. Further, during the change of the combustion mode, the change amount of the required torque PMCMD immediately before the change of the combustion mode is obtained, and the obtained change amount is converted into the fuel amount, thereby calculating the torque change amount correction term TCYLDPM.

  In step 31 following step 30, 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 up-count type post-switching elapsed time timer is set to a predetermined time TTCYLREF (for example, 6.0 sec) (step 32), and the provisional request The fuel injection amount TCYLLMT is set to the normal required fuel injection amount TCYLT (step 33), and the limit execution flag F_TCYLLMT is set to “0” (step 34), and the limit processing is prohibited.

  On the other hand, if the answer to step 31 is YES and PMCMD> 0, it is determined whether or not the switching status EMOD_STS is “0” (step 35). If the answer is YES and the combustion mode is not being switched, the steps 32 to 34 are executed.

  On the other hand, if the answer to step 35 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 36). If the answer is YES and the switching status EMOD_STS has not changed and the current loop is not immediately after the switching of the combustion mode, it is determined whether or not the limit execution flag F_TCYLLMT is “1” (step 37). When the answer is NO and the limit process is not executed, the steps 32 to 34 are executed. On the other hand, if the answer to step 37 is YES and the limit process is being executed, the process proceeds to step 39.

  On the other hand, when the answer to step 36 is NO and EMOD_STS ≠ EMOD_STSZ, that is, when the current loop is immediately after switching of the combustion mode, the timer value TTCYLMC of the post-switching elapsed time timer set in step 32 is set to the value 0. (Step 38), and the process proceeds to step 39.

  In this step 39, it is determined whether or not the timer value TTCYLMC of the post-switching elapsed time timer is smaller than the limit time TMTCYLMT. When the answer is YES, that is, when the limit time TMTCYLMT has not elapsed after switching of the combustion mode, it is determined whether or not the switching status EMOD_STS is “1” (step 40). If the answer is YES and the switching pattern is stratified combustion mode → stoichiometric combustion mode, a first limit value TCYLDS for this switching pattern is calculated (step 41). Next, the calculated first limit value TCYLDS is set as the provisional required fuel injection amount TCYLLMT (step 42), and the limit execution flag F_TCYLLMT is set to the value of the first limit value calculation flag F_TCYLDS (step 43).

  On the other hand, when the answer to step 40 is NO, steps 44 to 54 are executed in the same manner as steps 40 to 43 described above. First, in steps 44 and 45, it is determined whether or not the switching status EMOD_STS is “2” and “3”, respectively. When the answer to step 44 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 46). The value TCYLDL is set as the provisional required fuel injection amount TCYLLMT (step 47), and the limit execution flag F_TCYLLMT is set to the value of the second limit value calculation flag F_TCYLDL (step 48).

  If the answer to step 45 is YES (EMOD_STS = 3) and the switching pattern is stoichiometric combustion mode → stratified combustion mode, the third limit value TCYLSD for this switching pattern is calculated (step 49). The limit value TCYLSD is set as the provisional required fuel injection amount TCYLLMT (step 50), and the limit execution flag F_TCYLLMT is set to the value of the third limit value calculation flag F_TCYLSD (step 51). Further, when the answer to step 45 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 52). The limit value TCYLLD 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 fourth limit value calculation flag F_TCYLLD (step 54).

  On the other hand, if the answer to step 39 is NO and TTCYLMC ≧ TMTCYLMT, that is, if the limit time TMTCYLMT has elapsed after switching of the combustion mode, the steps 33 and 34 are executed assuming that the execution period of the limit process has ended. Then, the limit process ends.

  In step 55 following step 34, 43, 48, 51 or 54, it is determined whether or not a 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 56). If the answer is YES and the stratified combustion execution condition is not satisfied, the timer value TAFDTOS of the down-count delay timer is set to a predetermined standby time TMAFDTOS (eg, 3.0 sec) (step 57), and step 58 Proceed to On the other hand, when the answer to step 55 is NO and F_TCYLLMT = 0, or when the answer to step 56 is NO and F_DISCOK = 1, step 57 is skipped and the process proceeds to step 58.

  In step 58, it is determined whether or not the timer value TAFDTOS of the delay timer set in step 57 is 0. When this answer is NO, in order to prohibit the stratified combustion mode, the stratified combustion execution flag F_TAFDTOS0 is set to “0” (step 59), and this process is terminated. On the other hand, if the answer is YES and TAFDTOS = 0, the stratified combustion execution flag F_TAFDTOS0 is set to “1” (step 60), and this process is terminated.

  As apparent from steps 55 to 59 above, after the limit process is completed from the state in which 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 combustion mode is prohibited until the standby time TMAFDTOS elapses. Thereby, at the time of switching from the stratified combustion mode to the uniform combustion mode, it is possible to prevent the stratified combustion from being immediately executed according to the establishment of the execution condition of the stratified combustion or the end of the limit process.

  At the time of switching the combustion mode (step 35: NO), any one of the first to fourth limit values TCYLDS, TCYLDL, TCYLSD, and TCYLLD according to the switching pattern at that time is performed in steps 40 to 54. Is calculated, and a limit process using the calculated limit value is executed. Then, when the limit time TMTCYLMT elapses after the combustion mode is switched (step 39: NO), the limit processing is ended by the steps 33 and 34.

  Next, on behalf of the above first to fourth limit value calculation processes (steps 41, 46, 49, 52), executed at step 52, when switching from the lean combustion mode to the stratified combustion mode The fourth limit value TCYLLD calculation process will be described with reference to FIG.

  First, in step 70, the combustion efficiency parameter KTCLLD (combustion efficiency) is obtained by searching the KTCLLD table shown in FIG. 8 according to the timer value TTCYLMC of the post-switching elapsed time timer. In this table, the combustion efficiency parameter KTCLLD is set to gradually increase as the timer value TTCYLMC increases.

Next, at step 71, the fourth limit value TCYLLD is calculated by the following equation (1) using the combustion efficiency parameter KTCLLD, the fuel injection amount TCYLMMINI immediately before switching calculated at step 30 of FIG. 5 and the torque change amount correction term TCYLDPM. To do.
TCYLLD
= (TCYLMINI + TCYLDPM) × (1-KTCLLD) (1)

  The second term (1-KTCLLD) of this equation (1) represents the degree of increase in combustion efficiency with reference to immediately before switching. That is, the combustion efficiency is lower in the uniform combustion mode than in the stratified combustion mode in a low-load operation state where the combustion mode is switched. For this reason, at the time of switching from the uniform combustion mode to the stratified combustion mode, the combustion efficiency gradually increases, and accordingly, the required fuel injection amount TCYL for outputting the same torque tends to decrease. The combustion efficiency parameter KTCLLD represents the degree of increase in the combustion efficiency. Therefore, according to the table shown in FIG. 8 described above, the combustion efficiency parameter KTCLLD is set to gradually increase as the elapsed time after switching TTCYLMC increases. Therefore, by multiplying the second term (1-KTCLLD), the fourth limit value TCYLLD can be appropriately set according to the actual transition of the combustion efficiency after switching the combustion mode.

  Next, it is determined whether or not the calculated fourth limit value TCYLLD is larger than the requested fuel injection amount TCYLMINI immediately before switching (step 72). If the answer to this question is YES and the fourth limit value TCYLLD exceeds the fuel injection amount TCYLMINI immediately before switching, the fourth limit value TCYLLD is set to the fuel injection amount TCYLMINI immediately before switching (step 73). If NO, the process proceeds to step 74 as it is.

  The purpose of the steps 72 and 73 is as follows. As described above, since the combustion efficiency tends to increase when switching from the uniform combustion mode to the stratified combustion mode, the fourth limit value TCYLLD is usually smaller than the required fuel injection amount TCYLMINI immediately before switching, and step 72 is performed. The answer is no. On the other hand, if the auxiliary equipment is turned on during the limit process after the combustion mode is switched to the stratified combustion mode by turning off the auxiliary equipment such as an air conditioner during low load operation, the request is made accordingly. As the torque PMCMD increases, the fourth limit value TCYLLD may be excessively calculated. If limit processing is executed using the fourth limit value TCYLLD as it is, the air-fuel ratio may become extremely rich, and combustion may become unstable. The determination at step 72 assumes such a situation, and when the fourth limit value TCYLLD exceeds the fuel injection amount TCYLMINI immediately before switching, the fourth limit value TCYLLD is exceeded at step 73 by the fuel injection required immediately before switching. By setting the amount to TCYLMINI and maintaining the air-fuel ratio on the lean side, stable combustion can be ensured.

  In step 74 following step 72 or 73, it is determined whether or not the normal required fuel injection amount TCYLT is smaller than the fourth limit value TCYLLD. When the answer is YES, the fourth limit value calculation flag F_TCYLLD is set to “1” to indicate that the limit process based on the fourth limit value TCYLLD is being executed (step 75), and this process ends. .

  On the other hand, if the answer to step 74 is NO and TCYLT ≧ TCYLLD, it is assumed that the limit process cannot be performed with the fourth limit value TCYLLD, and the normal-time required fuel injection amount TCYLT is set as the fourth limit value TCYLLD (step). 76), in order to indicate that the calculation of the fourth limit value TCYLLD is completed, the fourth limit value calculation flag F_TCYLLD is set to “0” (step 77), and this process ends.

  Although not shown, the calculation processing (steps 41, 46, and 49) of the first to third limit values TCYLDS, TCYLDL, and TCYLSD is also basically performed in the same manner as the above-described fourth limit value TCYLLD. These limit values are also calculated according to the fuel injection amount TCYLMMINI immediately before switching, the torque change amount correction term TCYLDPM, and the combustion efficiency parameter.

  As described above, when the combustion mode is switched, the first to fourth limit values TCYLDS, TCYLDL, TCYLSD, and TCYLLD are calculated based on the required fuel injection amount TCYLMINI immediately before switching. The transition of the combustion mode can be performed smoothly without causing a step. Further, since the fourth limit value TCYLLD and the like are calculated according to the torque change amount correction term TCYLDPM, unlike the required fuel injection injection amounts TCYL1STT and TCYL2NDT for intake / compression stroke injection calculated according to the actual intake air amount, The fourth limit value TCYLLDS and the like can be appropriately set while favorably reflecting the change in the actual required torque PMCMD from immediately before switching to the time point. Furthermore, since the corresponding limit value is calculated according to the combustion efficiency parameter KTCLLD or the like, it can be set appropriately according to the actual combustion efficiency at that time. As described above, at the time of switching the combustion mode, the output torque of the internal combustion engine can be made to agree well with the required torque, thereby improving drivability.

  Next, an AF feedback control execution determination process based on the detection output of the LAF sensor 28 will be described with reference to FIG. First, in step 80, it is determined whether or not the fail safe detected flag F_FSPAFFB is “1”. If the answer is YES and the designated fail safe has already been detected, the limit cause prohibition flag F_TCYSTFB is set to “0” (step 81). As will be described later, this limit cause prohibition flag F_TCYSTFB is set to “1” in step 85 when AF feedback control is prohibited due to the fact that the limit process during combustion mode switching is being performed. is there. Next, the engine-side condition satisfaction flag F_AFFBD is set to “0” (step 82), and the feedback control permission flag F_AFFB is set to “0” (step 83), thereby prohibiting AF feedback control and performing this processing. finish.

  If the answer to step 80 is NO, it is determined whether or not a limit execution flag F_TCYLLMT is “1” (step 84). If the answer is YES and the limit process is being executed, it is determined that AF feedback control should be prohibited, and the limit cause prohibition flag F_TCYSTFB is set to “1” (step 85), and an up-count feedback control start delay is set. After the timer value TAFFBD of the timer is reset to 0 (step 86), the steps 82 and 83 are executed, and the AF feedback control is prohibited.

  When the answer to step 84 is NO and the limit process is not executed, it is determined whether or not the fuel cut flag F_FC or the expansion stroke injection execution flag F_SPGDIBC is “1” (step 87). The fuel cut flag F_FC is set to “1” during the execution of the fuel cut, and the expansion stroke injection execution flag F_SPGDIBC is set to “1” during the execution of the expansion stroke injection described above. When the answer to step 87 is YES and the fuel cut is being executed or the expansion stroke injection is being executed, the limit cause prohibition flag F_TCYSTFB is set to “0” (step 88) and the execution condition of the AF feedback control is If not established, the steps 86, 82 and 83 are executed, and AF feedback control is prohibited.

  When the answer to step 87 is NO and neither fuel cut nor expansion stroke injection is executed, it is determined whether or not the LAF sensor activation flag F_LAFACT is “1” (step 89). The LAF sensor activation flag F_LAFACT is set to “1” when it is determined from the estimated temperature of the catalyst device 17 that the LAF sensor 28 is activated. If the answer is NO and the LAF sensor 28 is not activated, the limit cause prohibition flag F_TCYSTFB is set to “0” (step 90), and the engine-side condition is determined that the AF feedback control execution condition is not satisfied. After the establishment flag F_AFFBD is set to “0” (step 91), step 83 is executed, and AF feedback control is prohibited.

  If the answer to step 89 is YES, it is determined that the execution condition is satisfied on the engine 3 side, and the engine-side condition satisfaction flag F_AFFBD is set to “1” to indicate that (step 92). Next, in step 93, it is determined whether or not the feedback control permission flag F_AFFB is “1”. If the answer is NO and the AF feedback control is not permitted, it is determined whether or not a limit cause prohibition flag F_TCYSTFB is “1” (step 94).

  When the answer to step 94 is NO, that is, when the cause of prohibiting the AF feedback control is due to the execution of fuel cut or expansion stroke injection other than the limit processing, the routine proceeds to step 95 and the intake air amount By searching a table (not shown) according to the parameter NTI, a table value TMAFFBD for other than the limit process is obtained and set as the control start determination value TAFBDR. The intake air amount parameter NTI is obtained by multiplying the basic fuel injection amounts TIM1ST and TIM2ND for intake or compression stroke injection calculated in step 5 or 6 of FIG. 2 by the engine speed NE, and the intake air per minute. Corresponds to air volume. The table value TMAFFBD is set to a timing at which a sufficient amount of exhaust gas reaches the LAF sensor 28 after the fuel cut or the expansion stroke injection is completed, and the air-fuel ratio KACT can be properly detected by the LAF sensor 28. ing.

  Next, it is determined whether or not the timer value TAFFBD of the feedback control start delay timer reset in step 86 is equal to or greater than the control start determination value TAFBDR (step 96). If the answer is NO and TAFFBD <TAFBDR, that is, if the time corresponding to the control start determination value TAFBDR has not elapsed after the end of fuel cut or expansion stroke injection, step 83 is executed, and AF feedback control is performed. Hold start of. On the other hand, if the answer to step 96 is YES and TAFFBD ≧ TAFBDR, it is determined that a sufficient amount of exhaust gas has reached the LAF sensor 28 and the air-fuel ratio KACT can be properly detected, so that the feedback control permission flag F_AFFB Is set to “1” (step 97), AF feedback control is started, and this process is terminated.

  On the other hand, when the answer to step 94 is YES, that is, when the cause of prohibiting the AF feedback control is due to execution of the limit process, the process proceeds to step 98, and the table ( The table value TMAFFBDT for limit processing is obtained by searching (not shown) and set as the control start determination value TAFBDR. This table value TMAFFBDT is set to a timing at which a sufficient amount of exhaust gas reaches the LAF sensor 28 after the limit process is completed, so that the air-fuel ratio KACT can be properly detected. It is set to a value different from the table value TMAFFBD for other than processing, for example, a smaller value.

  Next, it is determined whether or not the timer value TAFFBD of the feedback control start delay timer is equal to or greater than the control start determination value TAFBDR (step 99). If the answer is NO and the time corresponding to the control start determination value TAFBDR has not elapsed after the end of the limit process, step 83 is executed, and the start of AF feedback control is suspended. On the other hand, if the answer to step 99 is YES, it is determined that the air-fuel ratio KACT can be properly detected by the LAF sensor 28, and the limit cause prohibition flag F_TCYSTFB is set to “0” (step 100). 97 is executed to start AF feedback control.

  When AF feedback control is prohibited because the LAF sensor 28 is in an inactive state (step 89: NO), step 86 is not executed and the timer value TAFFBD of the feedback control start delay timer is reset. Not. Thereby, after the LAF sensor 28 is activated, the answer of step 96 is immediately YES, so that the AF feedback control can be started promptly.

  When the answer to step 93 is YES, if AF feedback control has already been performed, the process proceeds to step 97 to continue the AF feedback control.

  As described above, according to the present embodiment, since the AF feedback control is prohibited when the limit process is executed when the combustion mode is switched, the target air-fuel ratio KCMD1ST or KCMD2ND increases when the combustion mode is switched. Even if the change and the deviation from the detected air-fuel ratio KACT increase accordingly, fluctuations in the required fuel injection amount TCYL due to the AF feedback control corresponding thereto can be avoided. Thereby, the fluctuation | variation of the output torque and rotation speed of the engine 3 at the time of switching of combustion mode can be suppressed, and drivability can be improved.

  Further, when the AF feedback control is started after the inhibition, the control start determination value TAFBDR is set to a different value between the case after the end of the limit process and the case after the end of the fuel cut or the expansion stroke injection. Therefore, the AF feedback control can be started at an optimum timing according to the cause of the previous prohibition, and thereby the air-fuel ratio convergence by the AF feedback control can be improved. Further, the control start determination value TAFBDR can be appropriately set according to the intake air amount parameter NTI that is a multiplication value of the basic fuel injection amounts TIM1ST, TIM2ND and the engine speed NE.

  In addition, this invention can be implemented in various aspects, without being limited to the described embodiment. For example, in the embodiment, the control start determination value TAFBDR that determines the start timing of the AF feedback control is set according to the intake air amount parameter NTI. However, the present invention is not limited to this, and may be obtained by other appropriate methods. . Further, the present invention can be applied to various industrial cylinder injection type internal combustion engine control devices including an engine for a marine propulsion device such as an outboard motor having a crankshaft arranged in a vertical direction. It is. In addition, it is possible to appropriately change the detailed configuration within the scope of the gist of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control apparatus 2 ECU (Operating state detection means, request | requirement fuel amount calculation means, request | requirement torque calculation means,
Storage means, combustion efficiency estimation means, switching required fuel amount calculation means,
Air-fuel ratio detection means, target air-fuel ratio setting means, feedback control means,
(First and second feedback control prohibiting means, start timing setting means)
3 Engine 22 Crank angle sensor (Operating state detection means)
24 Air flow sensor (operating state detection means)
26 Intake pipe absolute pressure sensor (operating state detection means)
28 LAF sensor (air-fuel ratio detection means)
30 accelerator opening sensor (operating state detection means)
TCYL Required fuel injection amount (Required fuel amount)
PMCMD Required torque TCYLMINI Requested fuel injection amount immediately before switching
(Required fuel amount calculated just before the combustion mode is switched)
TCYLDPM Torque change amount correction term (requested torque calculated during switching)
KTCLLD combustion efficiency parameter (combustion efficiency)
TCYLDS first limit value (required fuel amount at switching)
TCYLDL 2nd limit value (required fuel amount at switching)
TCYLSD third limit value (required fuel amount at switching)
TCYLLD 4th limit value (required fuel amount at switching)
KACT detected air-fuel ratio KCMD1ST target air-fuel ratio for intake stroke injection KCMD2ND target air-fuel ratio for compression stroke injection TAFBDR control start determination value (start timing)

Claims (2)

A control device for an in-cylinder internal combustion engine that operates by switching a combustion mode between a stratified combustion mode for stratifying combustion of an air-fuel mixture and a uniform combustion mode for uniformly burning, and controls a fuel injection amount in accordance with a required fuel amount. There,
Operating state detecting means for detecting the operating state of the internal combustion engine;
A required fuel amount calculating means for calculating the required fuel amount according to the detected operating state of the internal combustion engine;
Requested torque calculating means for calculating a required torque of the internal combustion engine according to an operating state of the internal combustion engine;
Storage means for storing the required fuel amount calculated immediately before the combustion mode is switched;
Combustion efficiency estimating means for estimating the combustion efficiency of the internal combustion engine;
When the combustion mode is switched, the required fuel amount is switched according to the stored required fuel amount, the required torque calculated during the switching, and the combustion efficiency estimated during the switching. A required fuel amount calculation unit at the time of switching for calculating the required fuel amount during switching,
Air-fuel ratio detection means for detecting the air-fuel ratio of the air-fuel mixture burned in the internal combustion engine;
Target air-fuel ratio setting means for setting a target air-fuel ratio according to the required torque;
Feedback control means for performing feedback control of the required fuel amount so that the detected air-fuel ratio becomes the set target air-fuel ratio;
First feedback control prohibiting means for prohibiting feedback control by the feedback control means when the combustion mode is switched and the required fuel amount at the time of switching is calculated;
After the prohibition by the first feedback control prohibiting means, feedback that resumes feedback control at a predetermined timing that is estimated that the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine can be detected by the air-fuel ratio detecting means Control restarting means;
A control device for an internal combustion engine, comprising: A second feedback control prohibiting means for prohibiting the feedback control when a fuel cut for stopping fuel supply to the internal combustion engine is being executed;
The feedback control restarting means sets the predetermined timing to different timings after the prohibition by the first feedback control prohibiting means and after the prohibition by the second feedback control prohibiting means, The control device for an internal combustion engine according to claim 1.

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