Control device for internal combustion engine

Abstract

The present invention addresses the problem of obtaining a control device for an internal combustion engine, the control device being capable of both ensuring combustion stability and achieving PN suppression. A control device (150) for an internal combustion engine (10) according to the present invention performs, in accordance with a prescribed ignition retard amount based on the operation state of the internal combustion engine: ignition control based on an ignition timing which is delayed as compared to a required ignition timing set after catalyst warming-up; and injection control on at least two multistage fuel injections corresponding to a required injection amount in one combustion cycle. Under a condition that the ignition retard amount is smaller than a first threshold value (1201), a weak stratified-charge combustion mode in which a fuel injection timing is set to a compression stroke (803) is selected, and under a condition that the ignition retard amount is greater than or equal to the first threshold value (1201), a first stratified-charge combustion mode in which the fuel injection timing is set to an expansion stroke (804) is selected. The fuel injection amount or injection period is controlled such that an injection ratio in the first stratified-charge combustion mode is smaller than an injection ratio in the weak stratified-charge combustion mode.

Description

Control device for internal combustion engine

[0001] The present invention relates to a control device for controlling a fuel injection device of an internal combustion engine.

[0002] In recent years, with the tightening of exhaust emission regulations, engines are required to reduce the total amount and number of unburned particulate matter (PM), the unburned particle number (PN), which is the number of particles, as well as HC (hydrocarbons) and NOx (nitrogen oxides) during mode driving. PN and HC are generated when fuel injected from a fuel injector adheres to the piston and bore walls of the combustion chamber. The number of unburned particles tends to increase when the equivalence ratio (air-to-fuel ratio) is high immediately before ignition, i.e., when the fuel is rich. In other words, reducing fuel adhesion is effective in suppressing PN and HC. However, since HC is emitted in large amounts during engine startup when the catalyst is not yet activated, a technology is required to retard the ignition timing from idle after warm-up, increase exhaust loss, raise the exhaust temperature, and quickly warm up the catalyst.

[0003] In ignition retard, ignition is retarded from the optimal ignition timing that maximizes fuel economy. Specifically, ignition occurs during the expansion period between the end of the compression stroke and the piston's movement from top dead center to bottom dead center, which can easily lead to unstable combustion. Therefore, to ensure reliable ignition, a technology is required to create a rich (rich) mixture around the spark plug, which is necessary for ignition. Effective methods for creating a rich mixture around the spark plug at the time of ignition include forming a cavity on the piston crown, injecting fuel during the compression stroke, and stirring up the mixture that enters the cavity to concentrate the mixture around the spark plug, or positioning a fuel injector near the spark plug (center injection) and injecting fuel just before ignition. However, in the case of stratified charge combustion, which concentrates the mixture around the spark plug, the mixture becomes richer than the stoichiometric air-fuel ratio at the ignition timing, which can increase PN.

[0004] One method for reducing exhaust particulates containing PN as described above is disclosed in Patent Document 1. Patent Document 1 discloses a control method for suppressing PN generated after warm-up by switching from stratified combustion to homogeneous combustion after warm-up is complete.

[0005] JP 2022-93782 A

[0006] When the catalyst is warming up after starting the engine, it is effective to inject fuel just before ignition to ensure a stable mixture around the spark plug, which is necessary for combustion stability. This is particularly true for center-injection systems, where the fuel injection device is installed near the spark plug, as the spark plug and the fuel injection position are close together. Therefore, in order to form a mixture around the spark plug at the ignition timing, it is necessary to inject fuel just before the ignition timing. When fuel is injected just before the ignition timing, the time it takes for the fuel to vaporize is short, which increases the equivalence ratio, making the air-fuel ratio richer than the stoichiometric air-fuel ratio, which can increase PN.

[0007] The present invention has been made in consideration of the above points, and its purpose is to provide a control device for an internal combustion engine that can achieve both PN and combustion stability improvement and PN suppression under catalyst warm-up conditions after engine start.

[0008] The control device for an internal combustion engine of the present invention that solves the above-mentioned problem is a control device for an internal combustion engine that performs ignition control using an ignition timing that is retarded from the required ignition timing set after catalyst warm-up, in accordance with a predetermined ignition retard amount based on the operating state of the internal combustion engine, and injection control of at least two multi-stage fuel injections corresponding to the required injection amount in one combustion cycle, wherein the control device selects a weak stratified combustion mode in which the fuel injection timing is set to the compression stroke when the ignition retard amount by the ignition control is smaller than a first threshold value, and selects a first stratified combustion mode in which the fuel injection timing is set to the expansion stroke when the ignition retard amount is equal to or greater than the first threshold value, and controls the fuel injection amount or injection period so that the injection ratio in the first stratified combustion mode is smaller than the injection ratio in the weak stratified combustion mode when calculating an injection ratio with the sum of the fuel injection amounts in one combustion cycle as the denominator and the fuel injection amount of the at least two injections immediately before the ignition timing as the numerator.

[0009] According to the present invention, under catalyst warm-up conditions, when the ignition retard amount is small, which makes it easier to ensure combustion stability, weak stratified combustion is performed to suppress PN, and when the ignition retard amount is large, stratified combustion is performed to ensure combustion stability, thereby providing a control device for an internal combustion engine that can achieve both combustion stability and PN suppression.

[0010] Further features related to the present invention will become apparent from the description of the present specification and the accompanying drawings. In addition, problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.

[0011] 1 is a schematic diagram of a case in which a fuel injection device, a pressure sensor, and a control device described in a first embodiment are mounted on a direct-injection engine. FIG. 2 is a longitudinal sectional view of a fuel injection device according to a first embodiment of the present invention, and a diagram showing the configuration of a drive circuit and an engine control unit (ECU) connected to the fuel injection device. FIG. 3 is an enlarged sectional view of a drive section structure of a fuel injection device according to a first embodiment of the present invention. FIG. 4 is a diagram showing a general injection pulse for driving a fuel injection device, timing of a drive voltage and a drive current supplied to the fuel injection device, and the relationship between a valve element displacement amount and time. FIG. 5 is a diagram showing details of a control device and an ECU (engine control unit) of an internal combustion engine according to a first embodiment of the present invention. FIG. 6 is a schematic diagram of a direct-injection engine according to a first embodiment of the present invention, which injects fuel directly into a cylinder of the engine. FIG. 7 is a diagram showing a configuration of an engine system according to the first embodiment. FIG. 8 is a diagram showing an example of injection control of a crank angle and injection timing according to the first embodiment, showing an example of injection control during stratified charge combustion. FIG. 9 is a diagram showing an example of injection control of a crank angle and injection timing according to the first embodiment, showing an example of injection control during weakly stratified charge combustion. 7 is a diagram showing the relationship between the ignition retard amount, COV, and PN in the weak stratified combustion mode and the stratified combustion mode of the first embodiment of the present invention. FIG. 8 is a projection diagram of a fuel spray injected from the orifice of the fuel injection device when viewed from the A-A' cross section of FIG. 6 toward the fuel injection device in the first embodiment. FIG. 9 is a diagram showing the relationship between the engine speed, the ignition retard amount, and COV at the time of engine start in the first embodiment. FIG. 10 is a diagram showing the distribution of rich equivalence ratios at the ignition timing in the weak stratified combustion mode and the stratified combustion mode in the second embodiment. FIG. 11 is a diagram showing an example of a control method for the weak stratified combustion mode and the stratified combustion mode in the second embodiment. FIG. 12 is a diagram showing an example of a control method for the first stratified combustion mode and the second stratified combustion mode in the third embodiment. FIG. 13 is a diagram showing the relationship between the injection pulse width and the injection amount supplied to the fuel injection device in the third embodiment. FIG. 14 is a diagram showing the relationship between the injection pulse and the fuel injection amount.

[0012] [First Embodiment] Hereinafter, a fuel injection system including a fuel injection device and a control device according to this embodiment will be described.

[0013] First, a description will be given of the configuration of a fuel injection system 100. Fig. 1 is a schematic diagram of a case in which the fuel injection device, pressure sensor, and control device described in the first embodiment are mounted on an engine (direct injection engine) that is an internal combustion engine of a cylinder direct injection type.

[0014] Fuel injection devices 101A to 101D are installed in each cylinder so that fuel spray from their injection holes is injected directly into combustion chamber 107. Fuel is pressurized by fuel pump 106 and sent to fuel pipe 105, and then delivered to fuel injection devices 101A to 101D. Fuel pressure varies depending on the balance between the flow rate of fuel discharged by fuel pump 106 and the amount of fuel injected into each combustion chamber 107 by the fuel injection device provided for each cylinder of the engine, but the amount of fuel discharged from fuel pump 106 is controlled based on information from pressure sensor 102, with a predetermined pressure as a target value.

[0015] Fuel injection from fuel injection devices 101A to 101D is controlled by an injection pulse width sent from an engine control unit (ECU) 104. This injection pulse is input to a drive circuit 103 of the fuel injection device, which determines a drive current waveform based on a command from ECU 104 and supplies the drive current waveform to fuel injection devices 101A to 101D for a period based on the injection pulse. Note that drive circuit 103 may be implemented as a component or board integrated with ECU 104. A device in which drive circuit 103 and ECU 104 are integrated is referred to as a control device 150. Furthermore, fuel injection devices 101A to 101D may also be simply referred to as fuel injection devices 101.

[0016] Next, a description will be given of the configuration and basic operation of the fuel injection device 101 and its control device 150. Figure 2 is a vertical cross-sectional view of the fuel injection device 101 and a diagram showing an example of the configuration of the control device 150 for driving the fuel injection device 101. In Figure 2, the same symbols are used for parts that are equivalent to those in Figure 1.

[0017] The control device 150 includes a drive circuit 103 and an ECU 104. The ECU 104 includes a CPU and a memory, and realizes various functions by executing software programs stored in the memory with the CPU, and includes, for example, a fuel injection control unit as an internal function.

[0018] The fuel injection control unit of the control device 150 receives signals indicating the engine status from various sensors and calculates the width and timing of an injection pulse to control the amount of fuel injected from the fuel injector in accordance with the engine operating conditions. The ECU 104 is equipped with an A / D converter and an I / O port for receiving signals from the various sensors. The injection pulse output from the ECU 104 is input to a drive circuit 103 of the fuel injector 101 via a signal line 110. The drive circuit 103 controls the voltage applied to the solenoid 205 and supplies current. The ECU 104 communicates with the drive circuit 103 via a communication line 111, and is able to switch the drive current generated by the drive circuit 103 and change the current and time settings depending on the pressure of the fuel supplied to the fuel injector 101 and the operating conditions.

[0019] Next, the configuration and operation of the fuel injection device will be described. Figure 3 is an enlarged cross-sectional view of the drive structure of the fuel injection device according to this embodiment. Note that in Figure 3, the same reference numerals are used for parts that are the same as those in Figure 2.

[0020] The fuel injection device 101 is a normally closed solenoid valve (electromagnetic fuel injection device). When the solenoid 205 is not energized, the valve element 214 is biased in the valve closing direction by the first spring 210, and the valve element 214 is in close contact with the valve seat 218, resulting in a closed valve state. In the closed valve state, a force acting in the valve opening direction by the return spring 212 of the second spring acts on the armature 202. At this time, the force acting on the valve element 214 by the spring 210 is greater than the force by the return spring 212, so that an end face 302 of the armature 202 contacts the valve element 214, and the armature 202 remains stationary. The valve element 214 and the armature 202 are configured to be relatively displaceable and are contained within the nozzle holder 201. The nozzle holder 201 has an end face 303 that serves as a spring seat for the return spring 212. The force of the spring 210 is adjusted during assembly by the amount of pressure applied to a spring retainer 224 fixed to the inner diameter of the fixed core 207 .

[0021] In addition, the fuel injection device has a magnetic circuit formed by a fixed core 207, a movable element 202, a nozzle holder 201, and a housing 203, with a gap between the movable element 202 and the fixed core 207. A magnetic restriction 211 is formed in a portion of the nozzle holder 201 corresponding to the gap between the movable element 202 and the fixed core 207. The solenoid 205 is attached to the outer periphery of the nozzle holder 201 while being wound around a bobbin 204. A rod guide 215 is provided near the tip of the valve element 214 on the valve seat 218 side so as to be fixed to the nozzle holder 201. The movement of the valve element 214 in the valve axis direction is guided by two sliding points: the spring seat of the valve element 214 and the rod guide 215. An orifice 216 having a valve seat 218 and a fuel injection hole 219 is fixed to the tip of the nozzle holder 201, sealing the internal space (fuel passage) formed between the movable element 202 and the valve body 214 from the outside.

[0022] Fuel supplied to the fuel injector is supplied from a fuel pipe 105 located upstream of the fuel injector, flows through a first fuel passage hole 231 to the tip of the valve disc 214, and is sealed by a seat formed at the end of the valve disc 214 on the valve seat 218 side and the valve seat 218. When the valve is closed, fuel pressure generates a pressure difference between the top and bottom of the valve disc 214. The pressure difference, calculated by multiplying the fuel pressure by the pressure-receiving area of ​​the seat inner diameter at the valve seat position, and the load of the spring 210 push the valve disc 114 in the valve closing direction. When current is supplied to the solenoid 205 in the valve closed state, a magnetic field is generated in the magnetic circuit, and magnetic flux passes between the fixed core 207 and the armature 202, exerting a magnetic attraction force on the armature 202. When the magnetic attraction force acting on the armature 202 exceeds the pressure difference and the load of the spring 210, the armature 202 begins to displace toward the fixed core 207.

[0023] After the valve element 214 starts its valve-opening operation, the movable element 202 moves to the position of the fixed core 207 and collides with the fixed core 207. After colliding with the fixed core 207, the movable element 202 bounces back due to the reaction force from the fixed core 207, but the magnetic attraction force acting on the movable element 202 causes the movable element 202 to be attracted to the fixed core 207 and eventually stop. At this time, a force is applied to the movable element 202 in the direction of the fixed core 207 by the return spring 212, so the time until the bouncing converges can be shortened. Because the bouncing operation is small, the time during which the gap between the movable element 202 and the fixed core 207 becomes large is shortened, and stable operation can be performed even with a smaller injection pulse width.

[0024] After completing the valve-opening operation in this manner, the moving element 202 and the valve element 214 remain stationary in the open state. In the open state, a gap is formed between the valve element 214 and the valve seat 218, and fuel is injected from the fuel injection holes 219. The fuel flows downstream through a central hole in the fixed core 207 and a lower fuel passage hole 305 in the moving element 202.

[0025] When the solenoid 205 is de-energized, the magnetic flux generated in the magnetic circuit disappears, and the magnetic attractive force also disappears. As the magnetic attractive force acting on the armature 202 disappears, the armature 202 and the valve element 214 are pushed back to the valve-closed position in which they contact the valve seat 218 by the load of the spring 210 and the differential pressure.

[0026] Furthermore, when the valve element 214 closes from an open state, after the valve element 214 comes into contact with the valve seat 218, the movable element 202 separates from the valve element 214 and the movable element 202, moves in the valve closing direction, and after moving for a certain period of time, is returned to the initial position in the closed state by the return spring 212. By the movable element 202 separating from the valve element 214 at the moment the valve element 214 completes opening, the mass of the movable member at the moment the valve element 214 collides with the valve seat 218 can be reduced by the mass of the movable element 202. Therefore, the collision energy when the valve element 214 collides with the valve seat 218 can be reduced, and the bounding of the valve element 214 caused by the collision of the valve element 214 with the valve seat 218 can be suppressed.

[0027] In the fuel injection device 101 of this embodiment, the valve body 214 and the movable element 202 undergo relative displacement for a short period of time at the moment when the movable element 202 collides with the fixed core 207 when the valve is opened, and at the moment when the valve body 214 collides with the valve seat 218 when the valve is closed, thereby suppressing the bounding of the movable element 202 against the fixed core 207 and the bounding of the valve body 214 against the valve seat 218.

[0028] Next, we will explain the relationship between the injection pulse output from the ECU 104 in this embodiment and the drive voltage across the terminals of the solenoid 205 of the fuel injection device, the drive current (excitation current) and the displacement amount (valve body behavior) of the valve body 214 of the fuel injection device, and the relationship between the injection pulse and the fuel injection amount (Figure 4).

[0029] When an injection pulse is input to drive circuit 103, drive circuit 103 energizes switching elements 505 and 506 to apply high voltage 401 to solenoid 205 from a high voltage source boosted to a voltage higher than the battery voltage, thereby starting to supply current to solenoid 205. When the current value reaches a peak current value Ipeak pre-defined in ECU 104, application of high voltage 401 is stopped. Thereafter, when switching elements 505 and 506 are de-energized, diodes 509 and 510 are energized due to the back electromotive force caused by the inductance of fuel injector 101, and the current is fed back to voltage source VH, causing the current supplied to fuel injector 101 to rapidly decrease from peak current value Ipeak as shown by current 402. If switching element 506 is turned ON during the transition period from peak current value Ipeak to current 403, the current due to back electromotive force energy flows toward ground potential 515, the current regenerates within the circuit, a voltage of approximately 0 V is applied to solenoid 205, and the current gradually decreases. When the current value becomes smaller than predetermined current value 404, drive circuit 103 energizes switching element 508 and applies battery voltage VB by energizing and de-energizing switching element 507, providing a switching period during which control is performed to maintain predetermined current 403. If the fuel pressure supplied to fuel injector 101 increases, the fluid force acting on valve element 214 increases, and the time it takes for valve element 214 to reach the target opening becomes longer. As a result, the timing at which the target opening is reached may be delayed relative to the time required for the peak current value Ipeak to be reached, but if the current is reduced rapidly as in 402, the magnetic attractive force acting on the armature 202 also reduces rapidly, making the behavior of the valve element 214 unstable and, in some cases, causing the valve to start closing even while current is still flowing. If the switching switch 505 is turned ON to gradually reduce the current while the current is transitioning from the peak current value Ipeak to the current 403, the reduction in magnetic attractive force can be suppressed, ensuring the stability of the valve element 214 at high fuel pressures and suppressing variations in the injection amount.

[0030] The fuel injection device 101 is driven by this supply current profile. Between the application of the high voltage 401 and the time when the peak current value Ipeak is reached, the moving element 202 and the valve element 214 start to displace at timing t41, and then the moving element 202 and the valve element 214 reach their maximum height positions. At the timing when the moving element 202 reaches its maximum height position, the moving element 202 collides with the fixed core 207, and the moving element 202 performs a bounding motion between the moving element 202 and the fixed core 207.

[0031] Because the valve element 214 is configured to be displaceable relative to the armature 202, the valve element 214 separates from the armature 202, and the displacement of the valve element 214 overshoots beyond the maximum height position. Thereafter, the magnetic attraction force generated by the holding current 403 and the force of the return spring 212 in the valve opening direction cause the armature 202 to stop at a predetermined maximum height position, and the valve element 214 seats on the armature 202 and stops at the maximum height position, thereby achieving an open valve state. In the case of a fuel injection device having a movable valve in which the valve element 214 and the armature 202 are integrated, the amount of displacement of the valve element 214 does not exceed the maximum height position, and the amounts of displacement of the armature 202 and the valve element 214 after reaching the maximum height position are equal.

[0032] Next, a description will be given of the configuration of the engine control device in the first embodiment. Fig. 5 is a diagram showing details of the drive circuit 103 and ECU 104 of the fuel injection device.

[0033] The CPU 501 is built into the ECU 104, for example, and receives signals indicating the state of the engine 10 from the various sensors described above, such as the pressure sensor 102 attached to the fuel pipe 105 upstream of the fuel injection device 101, the A / F sensor that measures the amount of air flowing into the engine cylinder, the oxygen sensor that detects the oxygen concentration of exhaust gas discharged from the engine cylinder, and the crank angle sensor, and calculates the width and injection timing of an injection pulse to control the injection amount injected from the fuel injection device 101 in accordance with the operating conditions of the engine 10. The CPU 501 also calculates an appropriate pulse width (i.e., injection amount) and injection timing of an injection pulse width Ti in accordance with the operating conditions of the engine 10, and outputs the injection pulse width Ti to a drive IC 502 of the fuel injection device 101 through a communication line 504. The drive IC 502 then switches between energized and de-energized states of switching elements 505, 506, and 507 to supply a drive current to the fuel injection device 101.

[0034] Switching element 505 is connected between a high-voltage source higher than voltage source VB input to drive circuit 103 and a high-voltage terminal of fuel injector 101. Switching elements 505, 506, and 507 are configured, for example, by FETs or transistors, and can switch between energizing and de-energizing fuel injector 101. Boost voltage VH, which is the initial voltage value of the high-voltage source, is, for example, 60 V and is generated by boosting the battery voltage using boost circuit 514. Boost circuit 514 can be configured, for example, by a DC / DC converter or by a coil 530, transistor 531, diode 532, and capacitor 533. In the latter case, when transistor 531 is turned ON, battery voltage VB flows to ground potential 534. However, when transistor 531 is turned OFF, the high voltage generated in coil 530 is rectified through diode 532, and charge is accumulated in capacitor 533. This transistor is repeatedly turned on and off to increase the voltage of the capacitor 533 until it reaches the boosted voltage VH. The transistor 531 is connected to the IC 502 or the CPU 501, and the boosted voltage VH output from the boost circuit 514 is detected by the IC 502 or the CPU 501.

[0035] A diode 535 is provided between a power supply terminal 590 of the solenoid 205 and the switching element 505 so that a current flows from the second voltage source to the solenoid 205 and a ground potential 515. A diode 511 is also provided between the power supply terminal 590 of the solenoid 205 and the switching element 507 so that a current flows from the battery voltage source to the solenoid 205 and a ground potential 515. While the switching element 508 is energized, no current flows from the ground potential 515 to the solenoid 205, the battery voltage source, or the second voltage source. The ECU 104 is also equipped with a register and a memory for storing numerical data necessary for controlling the engine 10, such as calculating the injection pulse width. The register and memory are included in the control device 150 or the CPU 501 in the control device 150.

[0036] Furthermore, switching element 507 is connected between a low-voltage power supply and the high-voltage terminal of fuel injector 101. Low-voltage power supply VB is, for example, a battery voltage, and its voltage value is approximately 12 volts [V] to 14 volts [V]. Switching element 506 is connected between the low-voltage terminal of fuel injector 101 and ground potential 515. Drive IC 502 detects the value of the current flowing through fuel injector 101 using current detection resistors 508, 512, and 513, and switches switching elements 505, 506, and 507 between energized and de-energized states based on the detected current value, thereby generating the desired drive current. Diodes 509 and 510 are provided to apply a reverse voltage to solenoid 205 of the fuel injector to rapidly reduce the current supplied to solenoid 205. The CPU 501 communicates with the drive IC 502 via a communication line 503, and can switch the drive current generated by the drive IC 502 depending on the pressure of the fuel supplied to the fuel injection device 101 and the operating conditions. In addition, both ends of the resistors 508, 512, and 513 are connected to the A / D conversion port of the IC 502, and the IC 502 is configured to be able to detect the voltage applied to both ends of the resistors 508, 512, and 513.

[0037] Next, the configuration of the engine 10 and the fuel injection device 101 that are the subject of the control device in this embodiment, and an example of injection control will be described.

[0038] First, the configuration of the engine 10 according to this embodiment will be described. Figure 6 is a schematic diagram of an internal combustion engine (direct injection engine) of a cylinder type in which fuel is injected directly into the cylinder of the engine 10, showing a central cross section of the interior 615 of the engine 10. Note that Figure 6 illustrates the state of the fuel spray in the interior 615 of the engine 10 immediately after fuel is injected from the tip of the orifice 216 of the fuel injection device 101.

[0039] The engine 10 includes a fuel injector 101, a spark plug 604, an intake port 607, an exhaust port 608, a piston 609, an intake valve 605, and an exhaust valve 610. The fuel injector 101 and the spark plug 604 are provided in the cylinder head of the engine 10. The fuel injector 101 and the spark plug 604 are arranged adjacent to each other in pairs in each cylinder. The fuel injector 101 has a fuel injection hole for multi-stage fuel injection and is arranged at the center of the combustion chamber 107. The fuel injector 101 has a center injection structure that injects fuel from the center of the combustion chamber 107 along the axial direction of the cylinder. The fuel injection hole of the fuel injector 101 is arranged near the spark plug 604. The spark plug 604 is arranged in a position biased toward the exhaust valve 610 of the fuel injector 101. A piston t connected to a crankshaft (not shown) is accommodated in a cylinder of a cylinder block 614 of the engine 10 so as to be capable of reciprocating motion.

[0040] A crown surface 606 of piston 609 on the spark plug 604 side has a flat surface. A fixed partition wall 602 is attached to intake port 607 to block the flow to an upper portion 620 and a lower portion 611 of intake port 607. A valve 601 is provided upstream of the partition wall, and the opening and closing of valve 601 can be controlled by a control device. Figure 6 shows valve 601 in a closed state. Note that, for the sake of explanation, intake valve 605 and exhaust valve 610 are illustrated in Figure 6, but in a typical direct injection engine equipped with two intake valves 605 and two exhaust valves 610, intake valve 605 and exhaust valve 610 are not visible in a central cross section of cylinder interior 615.

[0041] Next, the system configuration of the engine 10 will be described. FIG. 7 is a configuration diagram of an engine system having the engine shown in FIG. 6. In FIG. 7, the same components and parts as those in FIGS. 1 and 6 are designated by the same reference numerals. Air flowing into the cylinder interior 615 passes through an air cleaner 701, a supercharging chamber 704 containing a supercharger turbine 702, an intercooler 705, a throttle valve 706, and an intake port 607. The air cleaner 701 is installed at the inlet and serves to remove dust particles from the air and prevent them from being drawn into the engine 10, thereby reducing wear on the internal components of the engine 10. The supercharging chamber 704 is also equipped with supercharger turbines 702 on both the intake and exhaust sides. The turbines 702 are connected by a shaft 707, which rotates the turbines 702 in response to the flow rate of the exhaust gas, increasing the amount of air flowing into the cylinder interior 615 and improving output. The air passing through the supercharging chamber 704 is cooled by an intercooler 705, passes through a throttle valve 706 that adjusts the amount of air, and an intake port 607, and then flows into the cylinder interior 615. In the cylinder interior 615, the air is mixed with fuel and ignited by a spark plug 604, resulting in combustion and transmitting driving force to a crankshaft 710. Then, during the expansion stroke, an exhaust valve 610 opens, discharging exhaust gases through an exhaust port 608, rotating the turbine 702 at the rate of its flow. The exhaust then passes through a catalyst 703, where it reduces HC, NOx, and CO before being discharged outside the vehicle. The catalyst 703 is, for example, a three-way catalyst, which uses palladium, rhodium, platinum, or the like to remove HC, NOx, and CO (carbon monoxide) contained in the exhaust gas through reduction and oxidation reactions. However, when the temperature is low, the reducing ability is low, and therefore, under low temperature conditions such as when the engine is started, combustion is required to quickly warm up the temperature of the catalyst 703 .

[0042] Next, an example of injection control of catalyst warm-up conditions by the control device of this embodiment and the configuration of the fuel injection device 101 will be described. FIG. 8 is a diagram showing an example of injection control in stratified charge combustion mode. In FIG. 8, the horizontal axis represents the crankshaft angle, with the TDC of the intake stroke corresponding to -360 degrees, the BDC corresponding to -180 degrees, and the TDC of the compression stroke corresponding to 0 degrees. The lift amount of the intake valve 605 is represented by a dotted line, the average turbulence velocity in the cylinder 615 is represented by a dashed line, and the tumble in the cylinder 615 is represented by a solid line. FIG. 11 is a projection diagram of the fuel spray injected from the orifice 216 of the fuel injection device 24, viewed from the A-A' cross section of FIG. 6 toward the fuel injection device. In FIG. 11, the same components as in FIG. 6 are designated by the same symbols.

[0043] Fuel injection device 101 in this embodiment is a multi-hole type fuel injection device having multiple fuel injection holes, and is composed of eight sprays, for example, sprays D1 and D2 directed toward spark plug 604, sprays D5, D6, D7, and D8 injected in a direction closer to intake valve 605, and sprays D3 and D4 directed toward piston 609. The concept is that during injection during the expansion stroke immediately before ignition, the air-fuel mixture formed by sprays D1 and D2 can be positioned around the area between negative electrode 612 and positive electrode 613 of spark plug 604.

[0044] Under catalyst warm-up conditions, intake valve 605 begins to open at timing t81 when piston 609 reaches top dead center (TDC) and immediately before or simultaneously with exhaust valve 610 closing, to draw air into combustion chamber 107. The fuel injection control unit of control device 150 causes fuel injector 101 to perform at least two multi-stage fuel injections corresponding to the required injection amount during one combustion cycle. In the example shown in FIG. 8 , fuel injector 101 injects the required injection amount during one combustion cycle in three injections. First, a first injection 805 is performed during intake stroke 802 at timing t82, between when intake valve 605 begins to open and when maximum lift is reached.

[0045] Thereafter, at timing t83 before the piston reaches bottom dead center (BDC), a second injection 806 is performed. Then, after the piston reaches BDC and enters the compression stroke 803, and the piston 609 reaches TDC, a third injection 807 is performed at timing t84 immediately before the ignition timing t86.

[0046] With this third injection 807, the spray injected from the fuel injection device 101 is placed as a mixture around the spark plug 604, and the control device 150 controls the injection timing so as to form a mixture at the spark plug 604 that is richer in fuel (hereinafter referred to as rich) than the theoretical air-fuel ratio (hereinafter referred to as stoichiometric).

[0047] If the injection timing is set to the expansion stroke 804 in order to inject fuel immediately before the ignition timing, the time between the ignition timing and the end of the injection timing t85 becomes shorter, making it easier to maintain the air-fuel mixture around the spark plug 604. In this case, the fuel injection amount split ratio between the intake stroke 802 and the expansion stroke 804 should be set so that the intake stroke receives more fuel, preferably at about 8:2 or 9:1.

[0048] Ignition is performed immediately after timing t85, when a rich air-fuel mixture is formed around the area between the negative electrode 612 and the positive electrode 613 of the spark plug 604, to ignite the mixture. In order to ensure a good air-fuel mixture around the spark plug 604 at this ignition timing t86, it is advisable to bring the ignition timing t86 and the timing t85, when the third injection ends, close together. By injecting fuel during the expansion stroke 804 immediately before the ignition timing t86, a rich equivalence ratio is formed, and the coefficient of variation (COV) of the indicated mean effective pressure, which is an index of combustion stability, can be improved. However, the rich equivalence ratio amount increases, which may increase PN.

[0049] The higher the pressure of the fuel supplied to the fuel injector 101, the more the fuel injection control unit of the control device 150 controls the fuel injection timing immediately before the ignition timing (for example, the timings t85 and t92 at the end of fuel injection) to approach an ignition timing that is retarded from the required ignition timing. Increasing the fuel pressure shortens the fuel vaporization time, which has the effect of improving combustion stability.

[0050] The ignition timing is controlled by an ignition timing control device (not shown). The ignition timing control device is realized, for example, by executing a software program in the ECU 104 of the control device 150. The ignition timing control device has a catalyst warm-up control unit that executes ignition control using ignition timing that is retarded from the required ignition timing set after catalyst warm-up, in accordance with a predetermined ignition retard amount based on the operating state of the engine 10. The catalyst warm-up control unit sets the ignition timing to the expansion stroke 804 and executes ignition control that gradually increases the ignition retard amount from the start of control.

[0051] Next, an example of the configuration of catalyst warm-up injection control by the control device of this embodiment will be described. FIG. 9 shows an example of injection control in the weak stratified charge combustion mode. In FIG. 9, as in FIG. 8, the horizontal axis represents the crankshaft angle, with the TDC of the intake stroke corresponding to -360°, the BDC corresponding to -180°, and the TDC of the compression stroke corresponding to 0°. The lift amount of the intake valve 605 is shown by a dotted line, the average turbulence velocity in the cylinder 615 is shown by a dashed line, and the tumble in the cylinder 615 is shown by a solid line. FIG. 10 shows the relationship between the ignition retard amount and COV and PN. In FIG. 10, the characteristics of weak stratified charge combustion are shown by a dashed line, and the characteristics of stratified charge combustion are shown by a solid line. The ignition retard amount in FIG. 10 is defined as the amount of retardation from the optimal ignition timing MBT.

[0052] 9, when the injection start timing of the third injection 807 before the ignition timing is set to timing t91 of the compression stroke 803, the injected fuel flows and circulates within the combustion chamber 107, enabling weakly stratified combustion, which forms a slightly rich mixture over a relatively wide area around the area between the negative electrode 612 and the positive electrode 613 of the spark plug 604 at the ignition timing. In this case, the fuel split ratio between the intake stroke 802 and the compression stroke 803 should be, for example, about 6:4 or 7:3.

[0053] In weak stratified charge combustion, as shown by dashed line 1001 in FIG. 10 , the coefficient of variation (COV) of indicated mean effective pressure, which is an index of combustion stability, increases compared to stratified charge combustion, as shown by solid line 1002. However, under conditions where the ignition retard amount is smaller than threshold value 1006, the COV becomes smaller than COV threshold value 1005 preset in control device 150.

[0054] Therefore, the specified COV can be met even in the weak stratified combustion mode, and furthermore, PN is smaller than in the stratified combustion mode when compared under the same ignition retard amount conditions. This is because in the weak stratified combustion mode, the injection timing just before the ignition timing is the compression stroke, and the time from the injection timing to the ignition timing is longer than in the stratified combustion mode, so the fuel is more likely to vaporize and the rich equivalence ratio amount decreases.

[0055] Next, a method for controlling switching between the weak stratified combustion mode and the stratified combustion mode after engine start in this embodiment will be described. Figure 12 is a diagram showing the relationship between engine speed, ignition retard amount, and COV at engine start in the first embodiment. The ignition retard amount in Figure 12 is defined as the amount of retard from the optimal ignition timing MBT.

[0056] After engine start, if the ignition retard amount by the catalyst warm-up control unit is less than the first threshold value 1201, the fuel injection control unit of the control device 150 selects a weakly stratified combustion mode in which the ignition timing t93 is set to the expansion stroke 804 and the injection timing (the timing of the end of fuel injection t92) of the third injection 807 immediately before the ignition timing t93 is set to the compression stroke 803. This weakly stratified combustion mode can reduce PN (see FIG. 10 ). In particular, immediately after engine start, the temperatures of the combustion chamber 107 wall and the cylinder interior 615 are low, so selecting the weakly stratified combustion mode enhances the effect of reducing PN. Note that after engine start, homogeneous combustion may be performed for several cycles after cranking, in which fuel is injected during the intake stroke 802 to increase the temperature of the cylinder interior 615 and stabilize combustion.

[0057] When the ignition retard amount increases and exceeds the first threshold value 1201, the injection timing (the end timing t85) of the third injection 807 immediately before the ignition timing t86 is changed to the expansion stroke 804 (see FIG. 8 ), and control is performed to switch to a stratified combustion mode (first stratified combustion mode) in which fuel is injected immediately before the ignition timing t86 (see the start timing t84 and the end timing t85 in FIG. 8 ). As shown in FIG. 10 , as the ignition retard amount increases, COV increases. Therefore, by switching from the weak stratified combustion mode 1001 to the stratified combustion mode 1002, COV can be reduced and combustion stability can be ensured. Furthermore, even in the stratified combustion mode 1002, PN decreases as the ignition retard amount increases. Therefore, the control device 150 of this embodiment can reduce PN while ensuring combustion stability.

[0058] When the ignition retard amount further increases with an increase in engine speed in the first stratified combustion mode and exceeds the second threshold value 1203, the control device 150 performs control to switch from the first stratified combustion mode to the second stratified combustion mode.

[0059] Next, an example of a control method of the control device in this embodiment will be described. In the above example, the ignition retard amount is used as the threshold for determining whether to switch from the weak stratified combustion mode to the stratified combustion mode. However, the control device 150 may use the COV as the threshold for determining whether to switch from the weak stratified combustion mode to the stratified combustion mode.

[0060] The COV can be calculated from the waveform of the in-cylinder pressure inside the cylinder 615. The in-cylinder pressure can be measured by an in-cylinder pressure sensor installed in the combustion chamber 107, but it may also be estimated based on the engine operating state. The control device 150 acquires information about the in-cylinder pressure (in-cylinder pressure acquisition unit). After the engine starts, if the COV is smaller than a third threshold value 1202 preset in the control device 150, the control device 150 sets the weak stratified charge combustion mode and sets the fuel injection timing (end of fuel injection t92) immediately before the ignition timing to the compression stroke 803, as shown in FIG. 9 .

[0061] Then, in the weak stratified combustion mode, the COV increases as the ignition retard amount increases, and when the COV reaches the third threshold 1202 and becomes equal to or greater than the third threshold 1202, the fuel injection timing (end of fuel injection t85) immediately before the ignition timing t86 is set to the expansion stroke 804, and the engine transitions to the first stratified combustion mode. Switching from the weak stratified combustion mode to the first stratified combustion mode temporarily reduces the COV, but it increases as the ignition retard amount further increases. When the COV reaches the fourth threshold 1204, the engine transitions to the second stratified combustion mode. The fourth threshold 1204 is set to a value equal to or less than the third threshold 1202.

[0062] In this way, when the ignition retard amount is small and the COV is smaller than the third threshold value 1202, the weak stratified combustion mode is selected, which makes it possible to maintain combustion stability while lengthening the time from the end of injection time t92 of the injection immediately before the ignition timing to the ignition timing t93, thereby reducing the rich equivalence ratio amount at the ignition timing t93. As a result, the PN suppression effect is enhanced.

[0063] Furthermore, when the ignition retard amount increases in the weak stratified charge combustion mode and COV increases to reach the third threshold 1202, the fuel injection immediately before ignition timing t86 can be set to the expansion stroke 804, thereby switching to the first stratified charge combustion mode. As a result, under conditions where the ignition retard amount is large and combustion becomes unstable, a rich mixture is placed around the spark plug, improving COV. Under conditions where the ignition retard amount is large, the exhaust temperature rises and afterburning is promoted, which may reduce PN. Therefore, even when the first stratified charge combustion mode, in which fuel is injected immediately before ignition timing, is implemented, an increase in PN can be suppressed.

[0064] Using COV as the threshold for determining whether to switch from the weak stratified combustion mode to the first stratified combustion mode provides greater robustness than switching based on the ignition retard amount. Because COV may change even under the same operating conditions depending on factors such as ambient temperature, switching the combustion mode based on COV more reliably ensures combustion stability while suppressing PN. On the other hand, using the first threshold 1201 of the ignition retard amount to switch from the weak stratified combustion mode to the first stratified combustion mode allows switching without detecting COV, thereby reducing engine costs and the computational load on the control device 150.

[0065] When it is difficult to measure COV, the first threshold value 1201 of the ignition retard amount for switching from the weak stratified combustion mode to the first stratified combustion mode should be set to 15 to 25 degrees after the top dead center of compression, and the second threshold value 1203 of the ignition retard amount for switching from the first stratified combustion mode to the second stratified combustion mode should be set to approximately 35 to 45 degrees after the top dead center of compression.

[0066] Increasing the ignition retard amount reduces the flow at the ignition timing, slowing combustion and increasing COV. In particular, in the weak stratified charge combustion mode, the combustion limit is low, so COV increases around 15 to 25 degrees after top dead center of compression. If COV cannot be measured, setting a first threshold value 1201 and a second threshold value 1203 in advance in the control device 150 allows an appropriate combustion state to be selected according to the ignition retard amount, thereby achieving both COV and PN. Note that if COV is not measured, a sensor for measuring the in-cylinder pressure inside the cylinder 615 and COV calculations in the control device are not required, which has the effect of reducing system costs and the calculation load on the control device 150.

[0067] [Second embodiment] Next, the configuration and control method of an injection control device according to a second embodiment will be described. Fig. 13 is a diagram showing the distribution of rich equivalence ratios at ignition timing in the weak stratified combustion mode and the stratified combustion mode in the second embodiment. Fig. 14 is a diagram showing the configuration of injection control in (a) the weak stratified combustion mode and (b) the stratified combustion mode in the second embodiment. In Fig. 14, the same symbols are used for components equivalent to those in Fig. 8.

[0068] A characteristic feature of the second embodiment is that in the weak stratified combustion mode, the control device 150 controls the injection ratio between the injection 1407 immediately before the ignition timing t93 and the injections 1405 and 1406 before that so that the injection 1407 is larger than the injection ratio in the stratified combustion mode.

[0069] 13A, the injected fuel flows in the weak stratified charge combustion mode, and the air-fuel mixture is distributed over a wider area 1302 around the spark plug 604 than in the stratified charge combustion mode, so the control device 150 controls the fuel injection amount or injection period to be larger than in the stratified charge combustion mode. As a result, the equivalence ratio around the spark plug 604 can be secured, and the effect of improving combustion stability is enhanced.

[0070] 14B, in the stratified charge combustion mode, the control device 150 controls the injection amount or injection period of the fuel injection 1410 immediately before the ignition timing so as to reduce the ratio of the injection amount or injection period to the injections 1408 and 1409 immediately before the ignition timing. As a result, in the stratified charge combustion mode, as shown in FIG. 13B, a rich equivalence ratio 1301 is placed in a narrow range around the spark plug 604, and an increase in the rich equivalence ratio amount is suppressed while maintaining COV, thereby reducing PN.

[0071] For example, when the COV is equal to or less than the third threshold value 1202, the control device 150 switches to the weak stratified combustion mode, and when the COV exceeds the third threshold value 1202 in the weak stratified combustion mode, the control device 150 controls to the stratified combustion mode. The control device 150 calculates an injection ratio in which the sum of the fuel injection amounts in one combustion cycle is used as the denominator and the fuel injection amount of the fuel injection 807 immediately before the ignition timing (in the compression stroke 803 or the expansion stroke 804) out of the at least two injections is used as the numerator.

[0072] The control device 150 compares the injection ratio in the stratified combustion mode with the injection ratio in the weak stratified combustion mode, and controls the fuel injection amount or injection period so that the injection ratio in the stratified combustion mode is smaller than the injection ratio in the weak stratified combustion mode. By making the injection ratio in the stratified combustion mode smaller than that in the weak stratified combustion mode in the injection immediately before the ignition timing, a rich equivalence ratio 1301 can be formed in a narrow range around the spark plug 604, and combustion stability, i.e., COV, can be improved while suppressing an increase in the rich equivalence ratio.

[0073] [Third Embodiment] Next, the configuration and control method of an injection control device according to a third embodiment will be described. Fig. 15 is a diagram showing the configuration of injection control in stratified combustion mode in the third embodiment. Fig. 15(b) shows the injection control method in the third embodiment, and for comparison, Fig. 15(a) shows a diagram equivalent to Fig. 8 in the first embodiment. In Fig. 15(b), the same symbols are used for components equivalent to Fig. 8.

[0074] A characteristic feature of this embodiment is that, under conditions in which the ignition retard amount is increased in the stratified combustion mode to be equal to or greater than a second threshold value 1203 that is greater than the first threshold value 1201, the control device 150 controls the mode to enter the second stratified combustion mode in which the injection ratio of the injection 1507 before the ignition timing becomes greater than the injection ratio of the injection 1507 before the ignition timing to the injections 1505 and 1506 before that, as the ignition retard amount deviates from the second threshold value 1203.

[0075] When the injection amount or injection period of injection 1507 is reduced, the injection amount or injection period of intake stroke 802 is increased to adjust the average mixture amount in cylinder 615, but it is preferable to set the injection amount or injection period of second injection 1506 in the intake stroke to be increased without changing the injection amount or injection period of first injection 1505 in the intake stroke 802. Since the piston is close to TDC at injection start timing t82 for first injection 1505 in the intake stroke 802, increasing the injection amount may increase fuel adhesion and increase PN, but by increasing the injection amount or injection period of second injection 1506 in the intake stroke 802, it is possible to suppress fuel adhesion and reduce PN.

[0076] [Fourth Embodiment] Next, the configuration and control method of an injection control device according to a fourth embodiment will be described. FIG. 16 is a diagram showing the relationship between the injection pulse output from the ECU 104, the drive voltage across the terminals of the solenoid 205 of the fuel injection device, the drive current (excitation current), and the displacement (valve behavior) of the valve element 214 of the fuel injection device 101 in the fourth embodiment. In FIG. 16, the same symbols are used for components equivalent to those in FIG. 4. In FIG. 16, the injection pulse, drive voltage, drive current, and valve element displacement under the conditions of FIG. 4 are indicated by dashed lines, and the injection pulse, drive voltage, drive current, and valve element displacement in the fourth embodiment are indicated by solid lines. FIG. 17 is a diagram showing the relationship between the injection pulse and the fuel injection amount.

[0077] In the stratified charge combustion mode, the control device 150 in this embodiment controls the height position of the valve body 214 in a height position region lower than the maximum height position so that the injection immediately before the ignition timing changes over time as shown in 1601.

[0078] As the ignition retard amount increases, the time from TDC to ignition timing becomes longer, and the pressure inside the cylinder decreases, increasing the penetration of the spray. Therefore, the control device 150 controls the valve element 214 at a height position lower than the maximum height position to increase the pressure loss at the seat portion and reduce the penetration of the spray. This makes it easier to maintain the air-fuel mixture around the spark plug 604 at the ignition timing, improving combustion stability and reducing COV.

[0079] On the other hand, in the weak stratified charge combustion mode, the control device 150 performs pre-ignition injection during the compression stroke 803 and controls the valve element 214 so that the valve element 214 reaches its maximum height position. This increases the spray penetration force, causing the spray to flow and providing a rich mixture over a slightly wider area around the spark plug 604, improving combustion stability. As a result, the COV can be reduced.

[0080] Furthermore, in the stratified charge combustion mode, the control device 150 may decrease the maximum height position of the valve element 214 as the ignition retard amount increases. As the displacement of the valve element 214 decreases, pressure loss occurs at the seat portion of the valve element 214, slowing the spray flow rate. Therefore, even if the ignition timing is retarded and the in-cylinder pressure in the cylinder 615 at the injection timing decreases, it becomes easier to form an air-fuel mixture near the spark plug 604, improving combustion stability.

[0081] The control device 150 performs control to decrease the valve disc height as the ignition retard amount increases, but under conditions where the ignition retard amount is small, particularly in the weak stratified combustion mode, the control device 150 may also control the valve disc 214 to reach the maximum height position. As a result, the maximum height position of the valve disc 214 can be changed significantly depending on the ignition timing retard amount, making it easier to maintain the air-fuel mixture near the spark plug despite changes in in-cylinder pressure that change depending on the ignition timing retard amount.

[0082] Next, the injection quantity characteristic Q141 when the current waveform of Fig. 16 is used will be described with reference to Fig. 17. When the injection pulse width Ti does not reach a certain time, the force in the valve opening direction, which is the resultant force of the magnetic attractive force acting on the moving element 202 and the second spring 214, does not exceed the force in the valve closing direction, which is the load of the third spring 234, or the magnetic attractive force required for the moving element 202 to slide through the gap G3 cannot be secured even if the moving element 202 starts to displace, and the moving element 202 does not come into contact with the valve element 214. In this condition, the valve element 214 does not start opening, and fuel is not injected.

[0083] Furthermore, under conditions where the injection pulse width Ti is short and the injection amount is small, for example, as in 1701, the movable element 202 collides with the valve element 214, causing the valve element 214 to separate from the valve seat 218 and begin to lift. However, since the valve element 214 begins to close before reaching its maximum opening, the injection amount becomes smaller than the dashed dotted line 1720 extrapolated from the linear region 1730 where the relationship between the injection pulse width and the injection amount is linear.

[0084] Furthermore, for the pulse width of point 1702, the valve disc 214 begins to close immediately after reaching the maximum height position, and the trajectory of the valve disc 214 exhibits parabolic motion. Under these conditions, the kinetic energy of the valve disc 214 in the valve opening direction is large, and the magnetic attractive force acting on the armature 202 is also large, so the proportion of the time required for valve closing is large, and the injection amount is greater than that indicated by the dashed-dotted line 1720. A region 1740 in which the valve disc 214 does not contact the fixed core 207, i.e., the valve disc 214 does not reach the maximum lift position, and the trajectory of the valve disc 214 exhibits parabolic motion, is referred to as the half-lift region, and a region 1741 in which the valve disc 214 contacts the fixed core 207 is referred to as the full-lift region. The condition indicated by the solid line in FIG. 17 corresponds to the half-lift region.

[0085] At the injection pulse width of point 1703, the valve starts closing at the timing when the bounding of the valve disc 214, caused by the collision of the movable element 202 with the fixed core 207, is maximized. Therefore, the repulsive force generated when the movable element 202 and the fixed core 207 collide acts on the movable element 202, shortening the valve closing delay time from when the injection pulse is turned off until the valve disc 214 closes. As a result, the injection amount is smaller than that indicated by the dashed-dotted line 1720. Point 1704 indicates a state in which the valve starts closing at timing t44, immediately after the bounding of the valve disc 214 subsides. For injection pulse widths Ti greater than point 1704, the fuel injection amount increases substantially linearly with increasing injection pulse width Ti. In the region from the start of fuel injection to the injection pulse width Ti indicated by point 1704, the valve disc 214 does not reach the maximum height position, or even if the valve disc 214 reaches the maximum height position, the bounding of the valve disc 214 is unstable, resulting in fluctuations in the injection amount. Since the fuel injection immediately before the ignition timing has a large impact on combustion stability when the injection amount fluctuates, it is advisable to adjust the injection pulse width in the half-lift region 1440 or the linear region, thereby improving combustion stability.

[0086] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the present invention as defined in the claims. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0087] 10: Engine (internal combustion engine) 100: Fuel injection system 101: Fuel injection device 150: Control device 604: Spark plug

Claims

1. A control device for an internal combustion engine that performs ignition control with an ignition timing retarded from a required ignition timing set after catalyst warm-up according to a predetermined ignition retard amount based on the operating state of the internal combustion engine, and injection control of at least two-stage multi-injection corresponding to a required injection amount during one combustion cycle, wherein the control device selects a weak stratified combustion mode in which the fuel injection timing is set in the compression stroke under the condition that the ignition retard amount by the ignition control is smaller than a first threshold value, and selects a first stratified combustion mode in which the fuel injection timing is set in the expansion stroke under the condition that the ignition retard amount is equal to or greater than the first threshold value. When obtaining an injection ratio with the sum of the fuel injection amounts during one combustion cycle as the denominator and the fuel injection amount immediately before the ignition timing among the at least two injections as the numerator, the fuel injection amount or injection period is controlled so that the injection ratio in the first stratified combustion mode is smaller than the injection ratio in the weak stratified combustion mode. A control device for an internal combustion engine characterized by this.

2. The control device for an internal combustion engine according to claim 1, wherein, under the condition that the ignition retard amount in the first stratified combustion mode is equal to or greater than a second threshold value greater than the first threshold value, as the ignition retard amount deviates from the second threshold value, a second stratified combustion mode in which the injection ratio is increased more than in the first stratified combustion mode is shifted to.

3. The control device for an internal combustion engine according to claim 2, wherein the control device performs control to bring the fuel injection timing immediately before the ignition timing closer to an ignition timing retarded from the required ignition timing as the pressure of the fuel supplied to the fuel injection device is higher.

4. A control device for an internal combustion engine that performs ignition control with an ignition timing retarded from a required ignition timing set after catalyst warm-up according to a predetermined ignition retard amount based on the operating state of the internal combustion engine, and injection control of at least two-stage fuel injection corresponding to a required injection amount during one combustion cycle, wherein the control device selects a weak stratified combustion mode in which the fuel injection timing is set in the compression stroke under the condition that the rate of change of the indicated mean effective pressure in the cylinder calculated from the in-cylinder pressure of the internal combustion engine is smaller than a third threshold value, and selects a first stratified combustion mode in which the fuel injection timing is set in the expansion stroke under the condition that the rate of change of the indicated mean effective pressure is equal to or greater than the third threshold value. When obtaining an injection ratio with the total fuel injection amount during one combustion cycle as the denominator and the fuel injection amount immediately before the ignition timing among the at least two injections as the numerator, the fuel injection amount or injection period is controlled so that the injection ratio in the first stratified combustion mode is smaller than the injection ratio in the weak stratified combustion mode. A control device for an internal combustion engine characterized by this.

5. The fuel injection device that performs the multi-stage fuel injection is provided in the internal combustion engine, and the fuel injection holes of the fuel injection device are arranged in the vicinity of the spark plug of the internal combustion engine. The control device for an internal combustion engine according to claim 1, characterized by this.

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