Fuel injection control device and fuel injection control method

Abstract

Provided is a fuel injection control device for controlling a fuel injection device capable of injecting fuel a plurality of times in one combustion cycle of an internal combustion engine, said fuel injection control device comprising a control unit that performs control such that, when the environmental temperature of the internal combustion engine at the starting or re-starting of the internal combustion engine is lower, there is a greater increase in the injection amount in a later fuel injection among a plurality of fuel injections in a compression stroke.

Description

[Technical Field]

[0001] The present invention relates to a fuel injection control device and a fuel injection control method for controlling a fuel injection device that injects fuel into a combustion chamber of an internal combustion engine. [Background technology]

[0002] Internal combustion engines must comply with exhaust regulations, and it is expected that exhaust regulations will become stricter and the exhaust measurement temperature will be expanded in the future. In other words, there is a demand for reducing emissions at lower temperatures (reducing unburned particles, etc.) than under previous exhaust regulations. When performing catalyst warm-up operation after engine start, sufficient combustion stability must be ensured to retard the ignition timing. For example, it is known that early catalyst warm-up is essential to reduce emissions when starting the engine at low outside temperatures such as -7°C.

[0003] Retarding the ignition timing during catalyst warm-up causes ignition to occur during the expansion stroke after top dead center of compression, burning the mixture. Therefore, retarding the ignition timing during catalyst warm-up can easily lead to unstable combustion. Therefore, combustion stability can be improved by placing a rich mixture around the spark plug and forming a stratified mixture toward the wall of the combustion chamber (the end of the combustion chamber). An effective method for forming a rich stratified mixture around the spark plug is to create a cavity in the piston and inject fuel during the compression stroke. Spraying fuel into the cavity causes the mixture to be stirred up, allowing a rich mixture to collect around the spark plug.

[0004] Patent Document 1 discloses a fuel injection control method that improves combustion stability while suppressing HC and PN emitted from the combustion chamber when the catalyst is warmed up after engine start by injecting fuel at least twice during the compression stroke. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-204447 A Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, future stricter exhaust emission regulations will require reduced emissions at low temperatures. During cold start, environmental temperatures around the engine, including fuel temperature, fuel injector temperature, coolant temperature, and piston and combustion chamber wall temperatures, are reduced. In particular, the reduced fuel and fuel injector temperatures increase fuel viscosity, reducing the spray penetration and vaporization rate within the combustion chamber. Reduced coolant temperature and piston and combustion chamber wall temperatures also reduce the spray temperature, resulting in reduced spray penetration and vaporization rate. When the fuel injection control disclosed in Patent Document 1 is performed during cold start, the equivalence ratio of the mixture in the combustion chamber decreases overall due to insufficient spray penetration and reduced vaporization rate, even though the mixture is stratified. Furthermore, a fuel-rich (hereinafter referred to as "rich") mixture does not reach the area around the spark plug, which poses a problem of insufficient combustion stability required for retarding the ignition timing during catalyst warm-up during cold start.

[0007] Given the above circumstances, it was desirable to ensure combustion stability so that ignition timing could be stably retarded to warm up the catalyst when starting or restarting the engine, even when the engine's ambient temperature was low. [Means for solving the problem]

[0008] In order to solve the above problem, one embodiment of the fuel injection control device of the present invention is a fuel injection control device that controls a fuel injection device that can inject fuel multiple times during one combustion cycle of an internal combustion engine, and is equipped with a control unit that controls the injection amount to increase during the later fuel injection of multiple fuel injections during the compression stroke, the lower the environmental temperature of the internal combustion engine when the internal combustion engine is started or restarted. [Effects of the Invention]

[0009] According to at least one aspect of the present invention, even when the ambient temperature of the engine is low, combustion stability can be ensured when the engine is started or restarted, and ignition timing can be retarded stably to warm up the catalyst. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing an example of a fuel injection system including a fuel injection device according to a first embodiment of the present invention and an ECU. [Figure 2] 1 is a diagram showing an example of a vertical cross section of a fuel injection device according to a first embodiment of the present invention and an example of the configuration of an ECU connected to this fuel injection device. [Figure 3] 1 is an enlarged cross-sectional view of a drive portion structure of a fuel injection device according to a first embodiment of the present invention. [Figure 4] 3 is a timing chart showing the time variations of an injection pulse, a drive voltage, a drive current, and a valve element displacement amount when a fuel injection device is driven. [Figure 5] FIG. 2 is a circuit diagram showing details of an ECU of the fuel injection device according to the first embodiment of the present invention. [Figure 6] 1 is a schematic diagram showing an example of the configuration inside a cylinder of an engine and the periphery of the engine according to a first embodiment of the present invention. [Figure 7] 1 is a configuration diagram showing a part of an intake system and an exhaust system of an engine according to a first embodiment of the present invention. [Figure 8] 3 is a diagram showing an example of a crank angle, an injection timing, and a lift amount of a fuel injection valve in the first embodiment of the present invention. FIG. [Figure 9] 9 is a diagram showing the in-cylinder equivalence ratio distribution when the outside air temperature is normal and when the outside air temperature is low, when the fuel injection control shown by the solid line in FIG. 8 is performed. [Figure 10] 3 is a diagram showing the amount of fuel adhering to the combustion chamber wall surface and the piston crown surface under fuel injection control according to the first embodiment of the present invention. FIG. [Figure 11]9 is a diagram showing an in-cylinder equivalence ratio distribution near the ignition timing at low temperatures when the fuel injection control according to the first embodiment of the present invention shown by the broken line in FIG. 8 is performed. FIG. [Figure 12] FIG. 10 is a diagram showing an example of the crank angle, injection timing, and lift amount of the fuel injection valve when the PL injection in the latter part of the compression stroke is divided in the second embodiment of the present invention. [Figure 13] 13 is a diagram showing an in-cylinder equivalence ratio distribution near the ignition timing at an assumed low temperature when the fuel injection control indicated by the broken line in FIG. 12 is performed in the second embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, examples of embodiments of the present invention will be described with reference to the accompanying drawings. In this specification and the accompanying drawings, components having substantially the same functions or configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0012] First Embodiment [Fuel injection system configuration] A fuel injection system to which a fuel injection control device according to a first embodiment of the present invention is applied will be described with reference to FIGS. 1 to 11. FIG.

[0013] First, an outline of a fuel injection system according to a first embodiment will be described with reference to FIG. 1 is a schematic diagram showing an example of a fuel injection system according to a first embodiment. The fuel injection system 1 is an example in which the present invention is applied to a direct injection engine (an example of an internal combustion engine), but the present invention is not limited to this example. In this specification, the direct injection engine will be simply referred to as an "engine."

[0014] The direct injection engine according to this embodiment has four cylinders 108 (engine cylinders). The fuel injection system 1 has four fuel injection devices 101A to 101D corresponding to the four cylinders 108, and an ECU (Engine Control Unit) 150 as an example of a fuel injection control device. In the following description, when there is no need to distinguish between the fuel injection devices 101A to 101D, they will be referred to as "fuel injection device 101."

[0015] Fuel injection devices 101A-101D for side injection are installed in each cylinder 108 of the fuel injection system 1 so that atomized fuel is injected directly into the combustion chamber 107 from fuel injection holes 219 (see FIG. 2 described later). Fuel stored in a fuel tank (not shown) is pressurized by a fuel pump 106 and sent to a rail-shaped fuel pipe 105 via a high-pressure pipe 120, and then delivered from the fuel pipe 105 to each of the fuel injection devices 101A-101D. A pressure sensor 102 for measuring the pressure of the fuel in the fuel pipe 105 is installed at one end of the fuel pipe 105.

[0016] The fuel pressure in the fuel pipe 105 varies depending on the balance between the flow rate of the fuel discharged by the fuel pump 106 and the amount of fuel injected into each combustion chamber 107 by each fuel injector 101 .

[0017] In this embodiment, the ECU 150 controls the amount of fuel discharged from the fuel pump 106 based on sensor information (information indicating the fuel pressure value) output from the pressure sensor 102 so that the fuel pressure in the fuel pipe 105 becomes a predetermined target pressure value.

[0018] Fuel injection by fuel injection device 101 is controlled by an injection pulse (see FIG. 4 described later) sent from CPU 104 (an example of a control unit) of ECU 150. For example, a command in the form of an injection pulse (pulse signal) with an adjusted pulse width is input to a drive circuit 103 provided for each fuel injection device 101. Drive circuit 103 determines the waveform of a drive current based on the command (injection pulse) from CPU 104, and supplies drive current of the waveform to fuel injection device 101 for a period of time based on the pulse width.

[0019] When changing the injection amount during fuel injection in one combustion cycle (described later), the control unit of the fuel injection control device (CPU 104 of ECU 150) changes the current waveform that drives the fuel injection device (fuel injection device 101) based on the pulse width of the injection pulse. In this way, by changing the current waveform based on the pulse width of the injection pulse, the injection amount of fuel injected by the fuel injection device can be adjusted. For example, by changing the current value of the drive current supplied to the fuel injection device, the lift amount of the fuel injection valve (valve body 214 in FIG. 2 described later) changes, and the injection amount is adjusted. In addition, by changing the timing (switching between off and on) of the injection pulse sent from CPU 104 to drive circuit 103, the timing at which the fuel injection device injects fuel can be adjusted.

[0020] The drive circuit 103 and the CPU 104 of the ECU 150 may be mounted as an integrated component or board.

[0021] Next, the configurations and basic operations of the fuel injection device 101 and the ECU 150 will be described with reference to FIGS. FIG. 2 is a diagram showing an example of a vertical cross section of the fuel injection device 101 and an example of the configuration of the ECU 150 connected to this fuel injection device 101. FIG. 3 is an enlarged cross-sectional view of the drive structure of the fuel injection device 101.

[0022] The CPU 104 of the ECU 150 receives various signals indicating the state of the engine from various sensors, and calculates the width of an injection pulse, the current value of a drive current, and injection timing to control the amount of fuel injected from the fuel injection device 101 according to the operating conditions of the engine. The CPU 104 outputs an injection pulse corresponding to the calculation result to the drive circuit 103.

[0023] The CPU 104 is equipped with an A / D converter, an I / O port, etc. (not shown) for taking in signals from various sensors. The various sensors include, for example, a temperature sensor that measures the temperature of the engine's cooling water (one example of the engine's environmental temperature), a sensor that measures the engine's rotation speed (rotational speed) (for example, a sensor that detects the rotation angle of the engine's crankshaft (not shown)), a pressure sensor 102 that measures the fuel pressure in the fuel pipe 105, and an exhaust temperature sensor that measures the exhaust temperature.

[0024] An injection pulse output from the CPU 104 is input to the drive circuit 103 through a signal line 110. The drive circuit 103 controls the voltage applied to a solenoid 205 (an example of a coil) of the fuel injection device 101, and supplies a current to the solenoid 205. The CPU 104 is capable of communicating with the drive circuit 103 (a drive IC 502 in FIG. 5 , which will be described later) through a communication line 111. The CPU 104 can control the drive current generated by the drive circuit 103 to be switched depending on the pressure of the fuel supplied to the fuel injection device 101, operating conditions, etc., and can change the set values ​​for the drive current and the time for outputting the current.

[0025] Fuel injection device 101 is a normally closed solenoid valve (electromagnetic fuel injection device) and includes solenoid 205 as an example of a coil, movable element 202, fixed core 207, and a generally rod-shaped valve element 214 (an example of a fuel injection valve). In fuel injection device 101, when solenoid 205 is not energized, spring 210 urges valve element 214 in a valve closing direction (downward in the drawing), and valve element 214 is in close contact with valve seat 218 (closed valve state).

[0026] The movable element 202 is biased in the valve-opening direction by the return spring 212. In the valve-closed state, the force acting on the valve element 214 by the spring 210 is greater than the force of the return spring 212, so that the upper end surface 202A of the movable element 202 comes into contact with the flange portion 302 of the valve element 214, and the movable element 202 is in a stationary state.

[0027] Valve element 214 and movable element 202 are configured to be relatively displaceable, and are both contained within nozzle holder 201. Nozzle holder 201 has an end surface 303 therein that serves as a spring seat for return spring 212. The biasing force of spring 212 is adjusted during assembly by the amount of pressing of spring retainer 224, which is fixed to the inner diameter of fixed core 207.

[0028] In the fuel injection device 101, a magnetic circuit is formed by the fixed core 207, the movable element 202, the nozzle holder 201, and the housing 203. A gap 301 is provided between the movable element 202 and the fixed core 207. A magnetic restriction 211 is formed in a portion of the nozzle holder 201 that corresponds to the gap 301 (on the outer periphery of the gap 301), where the magnetic restriction 211 is formed by forming a groove in the circumferential direction on the outer periphery of the nozzle holder 201.

[0029] The solenoid 205 is wound around the bobbin 204 and attached to the outer periphery of the nozzle holder 201. A rod guide 215 is fixed to the nozzle holder 201 at a position near the tip of the valve element 214 on the valve seat 218 side. With this configuration, the valve element 214 is guided to move in the valve axis direction (the up and down direction in the drawing) by two sliding points: a sliding point where the flange 302 of the valve element 214 slides against the fixed core 207, and a sliding point where the valve element 214 slides against the rod guide 215.

[0030] An orifice 216 having a valve seat 218 and a fuel injection hole 219 formed therein is fixed to the tip of the nozzle holder 201. With this configuration, the tip of the valve body 214 comes into contact with the valve seat 218 of the orifice 216, thereby sealing the internal space (fuel passage) between the nozzle holder 201 and the tip of the valve body 214 (valve closed state).

[0031] When the fuel injection device 101 is in a valve-closed state, fuel supplied from the fuel pipe 105 to the fuel injection device 101 flows through the fuel passage hole 231 to the tip side of the valve element 214, but the tip part of the valve element 214 on the valve seat 218 side comes into contact with the valve seat 218 of the orifice 216, sealing the fuel injection hole 219, and therefore the fuel is not injected to the outside through the fuel injection hole 219. When the fuel injection device 101 is in a valve-closed state, a pressure difference occurs between the upper and lower parts of the valve element 214 due to the fuel pressure, and the valve element 214 is pushed in the valve-closing direction by the load of the spring 210 and the pressure difference calculated by multiplying the fuel pressure by the pressure-receiving area at the valve seat position.

[0032] When fuel injection device 101 is in a valve-closed state, if the supply of current to solenoid 205 begins, a magnetic field is generated in the magnetic circuit, and magnetic flux passes between fixed core 207 and movable element 202, causing a magnetic attractive force to act on movable element 202. At the timing when the magnetic attractive force acting on movable element 202 exceeds the differential pressure and the load of spring 210, movable element 202 begins to displace in a direction toward fixed core 207. Then, after valve element 214 begins the valve-opening operation in accordance with the movement of movable element 202, movable element 202 moves closer to fixed core 207 and collides with fixed core 207.

[0033] After the movable element 202 collides 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 the movable element 202 stops, completing the valve-opening operation. 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. Since the bouncing action 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 injection pulses of shorter pulse widths.

[0034] Having completed 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, allowing fuel to be injected through the fuel injection holes 219. The fuel supplied through the fuel passage hole 231 passes through a central hole formed in the fixed core 207 and a lower fuel passage hole 305 formed in the moving element 202, and flows downstream (towards the fuel injection holes 219).

[0035] After that, when the solenoid 205 of the fuel injection device 101 is de-energized, the magnetic flux generated in the magnetic circuit disappears, and the magnetic attractive force acting on the moving element 202 also disappears. When the magnetic attractive force acting on the moving element 202 disappears in this way, the moving element 202 and the valve element 214 are pushed back to the valve-closed position where they contact the valve seat 218 by the load of the spring 210 and the differential pressure.

[0036] In this way, when the valve disc 214 changes from the open state to the closed state, after the valve disc 214 comes into contact with the valve seat 218, the movable element 202 separates from the valve disc 214 and moves in the valve closing direction. After moving for a certain period of time, the movable element 202 is returned to its initial position in the closed state by the action of the return spring 212. That is, the movable element 202 separates from the valve disc 214 at the moment the valve disc 214 changes to the closed state. This makes it possible to reduce the mass of the movable element at the moment the valve disc 214 collides with the valve seat 218 by the mass of the movable element 202, thereby making it possible to reduce the collision energy when the movable element (substantially the valve disc 214) collides with the valve seat 218. Therefore, it is possible to suppress the bounding of the valve disc 214 caused by the collision of the valve disc 214 with the valve seat 218.

[0037] In the fuel injection device 101 according to this embodiment, a relative displacement occurs between the valve disc 214 and the movable element 202 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 disc 214 collides with the valve seat 218 when the valve is closed. This makes it possible to suppress the bounding of the movable element 202 against the fixed core 207 and the bounding of the valve disc 214 against the valve seat 218.

[0038] Next, the configuration of the ECU 150 according to the first embodiment will be described with reference to FIG. FIG. 5 is a circuit diagram showing details of the ECU 150 including the drive circuit 103 of the fuel injection device 101.

[0039] The ECU 150 includes a CPU 104 as an example of a control unit, and a drive circuit 103. For example, the drive circuit 103 has a built-in drive IC (Integrated Circuit) 502. The CPU 501 and the drive IC 502 can be collectively referred to as a control unit. The CPU 104 takes in signals (information) indicating the state of the engine output from various sensors, such as the pressure sensor 102, a temperature sensor that measures the temperature of engine coolant, an A / F (Air Flow) sensor, an oxygen sensor, and a crank angle sensor (not shown).

[0040] The pressure sensor 102 is attached to a fuel pipe 105 upstream of the fuel injection device 101 (see FIG. 1). The A / F sensor measures the amount of air flowing into the cylinder 108 (air-fuel ratio). The oxygen sensor detects the oxygen concentration of the exhaust gas discharged from the cylinder 108. Based on signals received from the various sensors, the CPU 104 calculates the pulse width (injection pulse width Ti) of an injection pulse, injection timing, etc., for controlling the amount of fuel injected from the fuel injection device 101 in accordance with the operating conditions of the internal combustion engine.

[0041] Then, the CPU 104 calculates the injection pulse width Ti (i.e., injection amount), injection timing, etc., and then outputs an injection pulse with the injection pulse width Ti at an appropriate timing to the driving IC 502 of the driving circuit 103 via the communication line 504. Thereafter, the driving IC 502 switches the energization / de-energization of the switching elements 505, 506, and 507 to supply a driving current to the fuel injection device 101 (solenoid 205).

[0042] The ECU 150 is equipped with a register and a memory for storing numerical data necessary for controlling the engine, such as calculating the injection pulse width. The register and the memory may be included in the CPU 104 or may be arranged outside the CPU 104. FIG. 5 shows an example in which the memory 104M (an example of a storage medium) is arranged outside the CPU 104.

[0043] The memory 104M may store a computer program that the CPU 104 uses to control the operation of the fuel injection device 101. In this case, the CPU 104 reads and executes the computer program stored in the memory 104M, thereby realizing all or part of the function of controlling the operation of the fuel injection device 101. Note that the CPU 104 may be replaced by another arithmetic processing device such as an MPU (Micro Processing Unit).

[0044] The switching elements 505, 506, and 507 are configured by, for example, FETs (Field Effect Transistors) or bipolar transistors, and can switch between energizing and de-energizing the fuel injector 101.

[0045] The switching element 505 is connected between a boost circuit 514 (high voltage source) that supplies a boost voltage VH and a high-voltage terminal (power supply terminal 590) of the solenoid 205 included in the fuel injection device 101. The boost voltage VH output by the boost circuit 514 is higher than a low voltage (battery voltage VB) that a low-voltage source (e.g., a battery) (not shown) supplies to the drive circuit 103. Here, the voltage value of the battery voltage VB is, for example, approximately 12 to 14 V. The boost voltage VH, which is the initial voltage value of the boost circuit 514, is, for example, 60 V, and is generated by boosting the battery voltage VB by the boost circuit 514.

[0046] The boost circuit 514 may be configured with, for example, a DC / DC converter or the like, or may be configured with a solenoid 530 (coil), a transistor 531 (switching element), a diode 532, and a capacitor 533, as shown in FIG. 5. In the boost circuit 514 shown in FIG. 5, when the transistor 531 is turned on, a current due to the battery voltage VB flows to the ground potential 534 via the solenoid 530. On the other hand, when the transistor 531 is turned off, a high voltage generated in the solenoid 530 is rectified through the diode 532, and a charge is accumulated in the capacitor 533. By repeatedly turning on and off the transistor 531, the voltage of the capacitor 533 rises to the boost voltage VH. The transistor 531 is connected to the driving IC 502 or the CPU 104, and its on / off state is controlled by the driving IC 502 or the CPU 104. The voltage output from the boost circuit 514 can be detected by the driving IC 502 or the CPU 501.

[0047] 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 boost circuit 514 (high voltage source) to the solenoid 205 and 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 a low voltage source (for example, a battery) to the solenoid 205 and ground potential 515. Therefore, while the switching element 506 is conducting, no current flows from ground potential 515 to the battery and boost circuit 514 via the solenoid 205.

[0048] Furthermore, switching element 507 is connected between a battery, which is a low-voltage power source, and power supply side terminal 590 of fuel injector 101. Switching element 506 is connected between a low-voltage side terminal of fuel injector 101 and ground potential 515. Drive IC 502 detects the value of a current flowing through fuel injector 101 (each part of drive circuit 103) using current detection resistors 508, 512, and 513. Drive IC 502 switches between energized and de-energized states of switching elements 505, 506, and 507 depending on the detected current value, thereby generating a desired drive current.

[0049] Diodes 509 and 510 are provided to apply a reverse voltage to solenoid 205 of fuel injection device 101 to rapidly reduce the current supplied to solenoid 205. CPU 104 communicates with drive IC 502 through communication line 503, and is able to switch the drive current generated by drive IC 502 depending on the pressure of the fuel supplied to fuel injection device 101 and the operating conditions. In addition, both ends of resistors 508, 512, and 513 are connected to an A / D conversion port of drive IC 502, and the voltage applied to both ends of resistors 508, 512, and 513 can be detected by drive IC 502.

[0050] Next, the relationship between the injection pulse output from the CPU 104, the drive voltage across the terminals of the solenoid 205 provided in the fuel injection device 101, the drive current (excitation current), and the displacement amount (valve body behavior) of the valve body 214 of the fuel injection device 101 will be explained with reference to Figure 4.

[0051] FIG. 4 is a timing chart showing the general changes over time in the injection pulse, drive voltage, drive current, and valve element displacement amount when the fuel injection device 101 is driven.

[0052] When an ejection pulse (ON) is input from the CPU 104 to the driving IC 502, the driving IC 502 energizes the switching elements 505 and 506 to apply a high voltage 401 (boosted voltage VH boosted by the boost circuit 514) higher than the battery voltage to the solenoid 205, thereby starting to supply current to the solenoid 205. The driving IC 502 adjusts the current value to the solenoid 205 to a peak current value I peak When the voltage reaches the predetermined value, the application of the high voltage 401 is stopped.

[0053] Thereafter, the driving IC 502 de-energizes the switching elements 505, 506, and 507. As a result, the diodes 509 and 510 are energized by the counter electromotive force due to the inductance of the fuel injector 101, and the current is fed back to the high-voltage power supply (booster circuit 514). The current supplied to the fuel injector 101 reaches a peak current value I 402. peak It drops rapidly from

[0054] The peak current value I peak The switching element 506 may be turned on during the transition period from the current 401 to the current 403 (holding current), and in this way the current due to the back electromotive force energy flows to the ground potential 515 side, the current is regenerated in the circuit, and a voltage of approximately 0 V is applied to the solenoid 205, causing the current to gradually decrease.

[0055] When the current value becomes smaller than a predetermined current value 404, the driving IC 502 turns on the switching element 506 and applies the battery voltage VB by turning on / off the switching element 507, thereby providing a switching period during which the predetermined current 403 is maintained.

[0056] Here, when the fuel pressure supplied to the fuel injection device 101 increases, the fluid force acting on the valve element 214 in the valve closing direction increases, and the time it takes for the valve element 214 to reach the target opening becomes longer. As a result, the peak current I peak However, if the current is rapidly reduced as in the case of current 402, the magnetic attraction force acting on the moving element 202 also rapidly decreases, causing the behavior of the valve element 214 to become unstable, and in some cases the valve may start to close even while the current is still flowing. peak A rapid decrease in the magnetic attractive force can be suppressed by turning on switching element 505 to gradually decrease the current during the transition from current 403 to current 404. This ensures the stability of valve element 214 at high fuel pressures and makes it possible to suppress variations in the injection amount.

[0057] The fuel injector 101 is driven by such a driving current profile. peak t , the movable element 202 and the valve element 214 are rotated at timing t 41 The displacement starts at time t , and then the movable element 202 and the valve element 214 reach the maximum height position. 42 At this moment, the movable element 202 collides with the fixed core 207, and the movable element 202 performs a bounding motion between the movable element 202 and the fixed core 207. Since the valve element 214 is configured to be displaceable relative to the movable element 202, the valve element 214 moves away from the movable element 202, and the displacement of the valve element 214 overshoots beyond the maximum height position. Thereafter, the magnetic attraction force generated by the current 403 and the force of the return spring 212 in the valve opening direction cause the movable element 202 to stop at a predetermined maximum height position, and the valve element 214 is seated on the movable element 202 and stops at the maximum height position, thereby achieving an open valve state (timing t43 ).

[0058] In the case of a fuel injection device having a movable valve in which the valve body and the moving element are integrated, the displacement of the valve body does not exceed the maximum height position, and the displacement of the moving element and the valve body after reaching the maximum height position is equal.

[0059] Next, the configuration inside the cylinder 108 of the engine according to the first embodiment and around the engine will be described with reference to FIG. Fig. 6 is a schematic diagram showing an example of the configuration inside a cylinder 108 of an engine and the surrounding area of ​​the engine in the first embodiment. Fig. 6 shows a schematic cross section at the center inside a cylinder 108 of the engine.

[0060] The engine 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. In a direct injection engine that includes two intake valves 605 and two exhaust valves 610, the intake valve 605 and the exhaust valve 610 are not visible in a cross section at the center of the cylinder 108, but for the sake of explanation, the intake valve 605 and the exhaust valve 610 are shown in FIG.

[0061] In the engine, a fuel injection device 101 is disposed so as to inject fuel toward a combustion chamber 107 from a direction (angle) intersecting the stroke direction of a piston 609 on the intake port 607 side. Fuel is injected into a cylinder 108 (combustion chamber 107) from the tip of an orifice 216 of the fuel injection device 101. In a direct injection engine, fuel is injected directly into the cylinder 108.

[0062] A cavity 606 (recess) is formed in the surface (crown surface) of piston 609 facing spark plug 604, and is lower than the upper end (right side in the drawing) of piston 609 facing spark plug 604. Cavity 606 has the function of temporarily holding at least a portion of the mixture made up of air taken in from intake port 607 and fuel injected from fuel injector 101.

[0063] In this embodiment, cavity 606 refers to the deepest portion (farthest from the spark plug 604 side) from the upper end of the crown surface of piston 609 on the spark plug 604 side. Cavity 606 is formed in a range such that an extension line 618 of a dashed dotted line drawn from a center gap 617 between negative electrode 612 and positive electrode 613 of spark plug 604 in the stroke direction (sliding direction) of piston 609 is within cavity 606. Center gap 617 is a region including an ignition position where a spark is generated between negative electrode 612 and positive electrode 613.

[0064] In this embodiment, cavity 606 is formed in a direction perpendicular to the stroke direction from intake port 607 (left side in the drawing) to exhaust port 608 (right side in the drawing) beyond the intersection with an extension 618 passing through center gap 617 of spark plug 604. With this configuration, the air-fuel mixture held in cavity 606 is positioned directly below center gap 617 of spark plug 604 (on extension 618). With this configuration, the air-fuel mixture in cavity 606 is pushed up toward spark plug 604, and can be effectively combusted by ignition by spark plug 604.

[0065] A fixed partition wall 602 is attached to the intake port 607 to separate the air flow between an upper flow path (first flow path) 620 and a lower flow path (second flow path) 611 of the intake port 607. A valve 601 that opens and closes (opens / shuts off) the lower flow path 611 side is provided upstream of the lower flow path 611. The valve 601 is configured so that its opening / closing can be controlled by the CPU 104 of the ECU 150. FIG. 6 shows the valve 601 in a closed state.

[0066] Next, a portion of the configuration relating to intake and exhaust in the engine will be described with reference to Fig. 7. Fig. 7 is a configuration diagram showing a portion of the intake system and exhaust system of the engine in the first embodiment.

[0067] Air is drawn into cylinder 108 (combustion chamber 107) of the engine from an intake port (not shown) through air cleaner 701, supercharging chamber 704, intercooler 705, throttle valve 706, and intake port 607. Air cleaner 701, which is provided at the entrance of supercharging chamber 704, removes dust from the drawn-in air, preventing dust from being drawn into the engine. This suppresses wear and tear on the inside of the engine.

[0068] The supercharger 702 is provided in the supercharger chamber 704. The supercharger 702 includes a compressor 702A disposed on the intake side for compressing air, a turbine 702B disposed on the exhaust side for being rotated by the flow of exhaust gas, and a shaft 707 connecting the compressor 702A and the turbine 702B. In the supercharger 702, the turbine 702B is rotated in accordance with the flow velocity of the exhaust gas, which in turn rotates the compressor 702A via the shaft 707. As a result, the air that has passed through the air cleaner 701 is compressed by the rotation of the compressor 702A and is then directed to the intercooler 705 side. This increases the amount of air that flows into the combustion chamber 107 of the engine, thereby improving engine output. The air that has passed through the supercharger chamber 704 is compressed by the compressor 702A, and therefore its temperature increases.

[0069] Intercooler 705 cools the air that has been compressed by compressor 702A and has increased in temperature. Throttle valve 706 adjusts the amount of air that flows into cylinder 108 (combustion chamber 107) from intake port 607. The opening of throttle valve 706 is controlled by ECU 150 based on the opening of an accelerator pedal (not shown) and the like.

[0070] An intake valve 605 is provided in the intake port 607. The lift amount of the intake valve 605 (and the exhaust valve 610) relative to a reference position is controlled by the ECU 150. When the intake valve 605 opens at a predetermined timing, air flows into the combustion chamber 107 of the engine.

[0071] In the combustion chamber 107 of the engine, the air that has flowed in is mixed with the fuel injected from the fuel injector 101 to form an air-fuel mixture, which is then ignited by the spark plug 604 and burned. The force generated by the combustion of this air-fuel mixture is transmitted to a crankshaft (not shown) via a piston 609 and a connecting rod 710.

[0072] The engine is provided with a cooling device for cooling the engine and maintaining an appropriate temperature. For example, a water-cooled cooling device removes heat generated in the engine by passing coolant through a water jacket (reference number omitted) provided around the cylinders 108 of the engine, thereby maintaining an appropriate temperature. The temperature of the engine coolant (hereinafter referred to as engine water temperature) is adjusted by a thermostat 711 provided in the water jacket. The engine water temperature is an example of an ambient temperature. A coupler for a temperature sensor is attached to the top of the thermostat 711. The temperature sensor (not shown) detects changes in the resistance value of the thermostat 711 via the coupler and outputs the detection result (output signal) to the ECU 150. The coolant is guided to a radiator (not shown) via the water jacket, thermostat 711, and radiator hose 712, where heat is dissipated.

[0073] When the exhaust valve 610 is opened during the expansion stroke, the exhaust gas generated by the combustion of the air-fuel mixture in the combustion chamber 107 passes through the exhaust port 608 and rotates the turbine 702B of the turbocharger 702. The exhaust gas that rotates the turbine 702B passes through the catalyst 703, where HC, NOx, and CO (carbon monoxide) are reduced before being discharged to the outside. The catalyst 703 is a three-way catalyst made of, for example, palladium, rhodium, platinum, or the like. The catalyst 703 removes the HC, NOx, and CO contained in the exhaust gas by causing reduction and oxidation reactions using the catalyst. Because the reduction ability of this catalyst 703 is low at low temperatures, combustion (catalyst warm-up) is required to quickly warm up the temperature of the catalyst 703 under low-temperature conditions, such as when the engine is started.

[0074] Next, a method for controlling fuel injection by the fuel injection device 101 in the first embodiment will be described with reference to FIG. FIG. 8 is a diagram showing an example of the crank angle, injection timing, and lift amount of the fuel injector (valve element 214) in the first embodiment. In FIG. 8, the horizontal axis represents the crank angle when the top dead center of the intake stroke is −360 [deg. ATDC (After Top Dead Center)], and the vertical axis represents the lift amount of the fuel injector. Note that the solid line represents fuel injection at an assumed normal temperature according to this embodiment, and the dashed line represents fuel injection at an assumed low temperature according to this embodiment. In this embodiment, as an example, the normal outside air temperature is 25°C, and the low temperature is −7°C. The lower the outside air temperature, the lower the engine water temperature, which is an example of environmental temperature.

[0075] Fuel injection control during catalyst warm-up will be described using the solid line in Figure 8. Under catalyst warm-up conditions, ECU 150 starts opening intake valve 605 when piston 609 reaches top dead center (TDC) and immediately before or simultaneously with exhaust valve 610 closing, thereby drawing air into combustion chamber 107. Fuel injector 101 performs fuel injection during intake stroke 801 at times t81 and t82, from when intake valve 605 starts opening until it reaches the maximum lift position. Then, fuel injector 101 injects fuel during compression stroke 802 when piston 609 reaches bottom dead center (BDC) and enters compression stroke 802, at times t83 and t84 before piston 609 reaches top dead center. This causes a mixture of the spray injected from the fuel injector 101 and air to enter the cavity 606 and push the mixture up from the cavity 606 in the direction of the spark plug 604 .

[0076] By controlling the fuel injection timing in this manner, it is desirable to form a mixture richer than the theoretical air-fuel ratio (hereinafter referred to as stoichiometry) near spark plug 604. That is, a rich mixture is formed around the area between negative electrode 612 and positive electrode 613 of spark plug 604 (center gap 617 in FIG. 6), and ignition is performed at timing t85 after top dead center to ignite and burn the mixture.

[0077] On the other hand, when the temperature of the engine cooling water is low, the fuel viscosity increases, which reduces the penetration power of the spray and causes fuel to adhere to the combustion chamber wall and the crown surface of the piston 609, making it impossible to ensure a rich mixture around the spark plug 604.

[0078] The fuel injection control and its effects in the first embodiment of the present invention will be described with reference to FIGS. 8 to 11. In this embodiment, a total of four fuel injections are assumed during the intake stroke and compression stroke. However, the technical concept of this embodiment also applies to multi-stage fuel injection, such as three or more fuel injections during at least the compression stroke. In the example shown in FIG. 8, for example, at injection start timing t81 during intake stroke 801, a first fuel injection 803 assuming normal temperature, indicated by a solid line, is performed when the outside air temperature is normal, and a first fuel injection 810 assuming low temperature, indicated by a dashed line, is performed when the outside air temperature is low. Thereafter, one fuel injection (timing t82) is performed during intake stroke 801, and two fuel injections (timings t83 and t84) are performed during compression stroke 802, and ignition is performed at timing t85 after top dead center of compression stroke 802.

[0079] In this embodiment, the duration of first injection 810 at an assumed low temperature during intake stroke 801 is shorter than the duration of first injection 803 at an assumed normal temperature. Similarly, the duration of second injection 811 at an assumed low temperature during intake stroke 801 is shorter than the duration of second injection 804 at an assumed normal temperature. Furthermore, the duration of first injection 805 at an assumed normal temperature during compression stroke 802 and the lift amount of valve element 214 are the same as those of first injection 812 at an assumed low temperature during compression stroke 802. Therefore, in FIG. 8, fuel injection 805 and fuel injection 812 overlap. Furthermore, the lift amount of valve element 214 by second injection 813 at an assumed low temperature during compression stroke 802 is greater than the lift amount by second injection 806 at an assumed normal temperature. In the example shown in FIG. 8, fuel injections 803-805 and 811-812 are full lift (hereinafter, referred to as FL) injections in which the valve element 214 is displaced to the maximum lift amount. Furthermore, the fuel injections 806 and 813 are partial lift (hereinafter referred to as PL) injections in which the valve body 214 does not displace to the maximum lift amount.

[0080] Next, the analysis results of the in-cylinder air-fuel mixture when fuel injection control is performed assuming normal temperature when the ambient temperature is low will be described with reference to FIG. FIG. 9 shows the equivalence ratio distribution in the cylinder when the outside air temperature is normal and when the outside air temperature is low, when the fuel injection control shown by the solid line in FIG. 8 is performed. The example shown in FIG. 9 shows the equivalence ratio distribution of the mixture in the cylinder after the third fuel injection in one combustion cycle (the first during the compression stroke), after the fourth fuel injection (the second during the compression stroke), and at the time of ignition. The equivalence ratio is a value that indicates how many times the theoretical air-fuel ratio there is fuel relative to the amount of air in the cylinder. In FIG. 9, the larger the value, the higher the equivalence ratio, indicating a richer mixture.

[0081] When the fuel injection control shown by fuel injections 803, 804, 805, and 806 in FIG. 8 is performed at engine start, a rich, stratified air-fuel mixture 901 is formed around spark plug 604 at ignition on the left side of FIG. 9, which assumes a normal temperature (25°C). On the other hand, on the right side of FIG. 9, which assumes a low temperature (-7°C), when the same fuel injection control is performed, a rich, stratified air-fuel mixture 903 gathers below spark plug 604 but does not rise up to spark plug 604. As a result, combustion stability is reduced at low temperatures compared to normal temperatures. One possible reason for this is that the penetration power of the third spray 902 decreases as the fuel viscosity increases with a decrease in ambient temperature, and even when the fourth injection is performed, the air-fuel mixture 903 is not pushed up around spark plug 604.

[0082] Therefore, in this embodiment, in order to solve the problem that a rich air-fuel mixture 903 does not rise to the vicinity of the spark plug 604 when the engine water temperature is low, fuel injection control is performed as shown by fuel injections 810, 811, 812, and 813 indicated by dashed lines in FIG. 8. The reason for performing multiple (e.g., two) fuel injections during the compression stroke is that the temperature of the air-fuel mixture rises due to compression, making the mixture more likely to vaporize. In this case, ECU 150 performs control to increase the current value of the drive current supplied to fuel injector 101, the pulse width of the injection pulse for applying a drive voltage to fuel injector 101, or the number of injections for fuel injection 813 during the latter part of the compression stroke 802 compared to fuel injection 806 assumed at room temperature. In this specification, the first fuel injection of the multiple fuel injections during compression stroke 802 is referred to as the "early fuel injection during the compression stroke," and the second and subsequent fuel injections are referred to as the "later fuel injection during the compression stroke." In the example of FIG. 8, in fuel injections 806 and 813 in the compression stroke 802, the injection amount is adjusted by changing the current value of the drive current.

[0083] By performing the above control, when the engine water temperature is low, the injection amount of fuel injection 813 assumed to be at a low temperature is increased compared to fuel injection 806 assumed to be at a normal temperature, thereby increasing the penetration force. In this way, the fuel injection control device (ECU 150) according to this embodiment changes the injection amount in the latter part of the compression stroke 802 according to the engine water temperature, thereby maintaining an appropriate penetration force. As a result, in this embodiment, even if the engine water temperature changes, a rich air-fuel mixture 903 can be pushed up near the spark plug 604, and a rich, stratified air-fuel mixture 903 can be collected below the spark plug 604. The relationship between the engine water temperature and the fuel injection amount is determined in advance by experiment or simulation, and is stored in memory 104M (FIG. 5) or a non-volatile recording medium as a look-up table (map data) or function data.

[0084] Furthermore, in this embodiment, the lower the engine water temperature, the greater the control to increase the current value of the drive current or the pulse width of the injection pulse during the later fuel injection in the compression stroke 802, and the greater the control to decrease the current value or pulse width during fuel injections 803 and 804 in the intake stroke 801. That is, in this embodiment, when the environmental temperature is relatively low, the fuel injection amount in the intake stroke 801 is reduced.

[0085] Here, the amount of fuel adhering to the wall surface of the combustion chamber 107 and the crown surface of the piston 609, which was revealed by the inventors' analysis of the air-fuel mixture, will be described with reference to FIG. Fig. 10 is a diagram showing the amount of fuel adhering to the combustion chamber wall surface and the piston crown surface under fuel injection control according to the first embodiment. In Fig. 10, the horizontal axis represents the crank angle [deg], with the top dead center of the intake stroke set to 0 degrees, and the vertical axis represents the amount of fuel adhering [mg]. The left side of Fig. 10 shows the amount of fuel adhering when injections 803, 804, 805, and 806 (see Fig. 8) are performed assuming a normal temperature when the outside air temperature is low (-7°C). The right side of Fig. 10 shows the amount of fuel adhering when fuel injections 810, 811, 812, and 813 are performed assuming a low temperature when the outside air temperature is low (-7°C). Specifically, the amount of fuel adhering to the wall surface 614 of the combustion chamber 107 is shown by solid lines 1001B and 1002B, the amount of fuel adhering to the crown surface of the piston 609 is shown by dashed lines 1001P and 1002P, and the total of these amounts of fuel adhering is shown by dashed lines 1001A and 1002A.

[0086] As shown in FIG. 10, the amount of fuel adhering to the wall surface of the combustion chamber 107 and the crown surface of the piston 609 can be reduced by reducing the pulse width of the injection pulse during fuel injection during the intake stroke (0 to 180 degrees) as the engine water temperature decreases. In the graph on the left side of FIG. 10, the amount of fuel adhering to the crown surface of the piston 609 during the intake stroke is large. In the graph on the right side of FIG. 10, the amount of fuel adhering is reduced by reducing the injection amount during the intake stroke and increasing the injection amount during the compression stroke (180 to 360 degrees). For example, as shown by solid line 1002B, the amount of fuel adhering to the wall surface of the combustion chamber 107 is almost zero. One factor that reduces the amount of fuel adhering is that the temperature and pressure inside the combustion chamber 107 increase during compression, making it easier for the fuel spray to vaporize.

[0087] Furthermore, with regard to the fuel injection amount, as shown in fuel injections 810 and 811 in FIG. 8 , it is possible to equalize the decrease in the fuel injection amount during the intake stroke 801 with the increase in the fuel injection amount during the later fuel injection during the compression stroke 802 at engine start, as described above, compared to fuel injections 803 and 804. That is, the fuel injection amount during one combustion cycle is made equal regardless of the engine coolant temperature. In the example of FIG. 8 , the injection amount during the intake stroke 801 is adjusted by changing the pulse width of the injection pulse. This fuel injection control makes it possible to increase the fuel injection amount during the later fuel injection during the compression stroke without changing the total fuel injection amount, even if the engine coolant temperature drops. As a result, this embodiment can achieve engine operation that suppresses deterioration in fuel efficiency during engine start-up due to a drop in ambient temperature.

[0088] In other words, expressed mathematically, "amount of decrease in fuel injection amount during the intake stroke = amount of increase in fuel injection amount during the compression stroke." Using FIG. 8, the fuel injection amount can be expressed as ["Fuel injection 803 - Fuel injection 810" + "Fuel injection 804 - Fuel injection 811"] = [Fuel injection 813 - Fuel injection 806]. In this embodiment, as the engine water temperature decreases, the fuel injection amount is increased during the compression stroke to push up the air-fuel mixture. This ensures a rich air-fuel mixture around spark plug 604 and improves combustion stability. Furthermore, in this embodiment, by making the amount of increase in fuel injection amount during the compression stroke equal to the amount of decrease in fuel injection amount during the intake stroke, the engine can be operated with sufficient combustion stability to implement ignition retard.

[0089] Next, a detailed description will be given of a method for controlling fuel injection in the later stage of the compression stroke. In the example shown in FIG. 8, fuel injections 806 and 813 in the later stage of the compression stroke 802 are performed by partial lift (PL) injection. In the later stage of the compression stroke 802, the geometric distance between the fuel injector 101 and the crown surface of the piston 609 becomes shorter. If fuel injection in the later stage of the compression stroke 802 is performed with a high spray penetration force, such as full lift (FL) injection, when pushing the mixture up around the spark plug 604, the rich mixture will pass around the spark plug 604. Not only will a rich mixture not be secured around the spark plug 604, but fuel will also adhere to the upper side of the combustion chamber 107. Therefore, in this embodiment, PL injection is performed in the fuel injections 806 and 813 that push up the mixture in the later stage of the compression stroke 802, thereby suppressing the spray penetration force. By performing PL injection, the penetration force of the spray can be maintained appropriately, and a rich mixture that contributes to combustion stability can be maintained around the spark plug 604.

[0090] However, even if full lift (FL) injection is used, if the penetration force of the spray is not higher than a predetermined value, fuel injection in the latter part of the compression stroke does not have to be performed as PL injection.

[0091] During catalyst warm-up, in order to create a rich, stratified air-fuel mixture around spark plug 604, cavity 606 must be used to swirl the mixture up to the area around spark plug 604. Therefore, just as with fuel injections 806, 813 by PL injection in the latter part of compression stroke 802, using cavity 606 for fuel injections 805, 812 by FL injection performed first in compression stroke 802 also makes it easier to collect a rich air-fuel mixture around spark plug 604. Therefore, it is desirable to start fuel injections 805, 812 by FL injection in the middle or later part of compression stroke 802. The middle part of the compression stroke here refers to the second period when the compression stroke is divided into three parts based on the crank angle.

[0092] Furthermore, in this embodiment, the fuel injection amount control for the later-stage PL injection during the compression stroke increases the current value of the drive current or the pulse width of the injection pulse as the engine water temperature decreases. In this case, the injection timing of the later-stage fuel injection during the compression stroke is not changed regardless of the engine water temperature. For example, the injection timing t84 is the same for fuel injection 806 assumed at normal temperature and fuel injection 813 assumed at low temperature. By performing the above control, even when the engine water temperature is low, the penetration force of the spray can be increased and the air-fuel mixture formed by FL injection during the compression stroke can be pushed up. Furthermore, according to this embodiment, ECU 150 only needs to calculate the injection amount for the later-stage fuel injection during the compression stroke in accordance with the engine water temperature; there is no need to calculate the fuel injection timing separately.

[0093] Next, the analysis results of the in-cylinder air-fuel mixture when the outside air temperature is low in the first embodiment will be described with reference to FIG. Fig. 11 is a diagram showing the in-cylinder equivalence ratio distribution near the ignition timing at low temperatures when the fuel injection control according to the first embodiment of the present invention shown by the dashed line in Fig. 8 is performed. As shown in Fig. 11, even if the engine water temperature drops when the engine is started, a rich, stratified air-fuel mixture 1101 can be collected around the spark plug 604 by performing fuel injections 810, 811, 812, and 813 assuming a low temperature. Furthermore, even when the engine water temperature drops, it can be seen that the equivalence ratio of the air-fuel mixture 1102 near the end of the combustion chamber 107 (the wall surface of the combustion chamber 107) also increases, compared to the analysis result at low temperatures on the right side of Fig. 9.

[0094] The reason for not changing the injection timing is that, as shown in FIG. 8, PL injection occurs during the latter half of the compression stroke, and the distance between fuel injector 101 and piston 609 is short. Here, the latter half of the compression stroke refers to the latter half when the compression stroke is divided into two parts based on the crank angle. That is, this is to eliminate changes in spray angle, penetration force, and spray roll-up due to in-cylinder pressure and flow velocity. Explaining this using the fuel injection pattern shown in FIG. 8, when the engine water temperature is low, the current value of the drive current or the pulse width of the injection pulse is increased at the timing of fuel injection 806, thereby increasing the fuel injection amount as in fuel injection 813. Therefore, in this embodiment, combustion stability can be ensured even when the engine water temperature is low.

[0095] As described above, the fuel injection control device (ECU 150) according to the first embodiment controls a fuel injection device (fuel injection device 101) that can inject fuel multiple times during one combustion cycle of an internal combustion engine (for example, an engine consisting of four cylinders 108). The fuel injection control device includes a control unit (CPU 104) that controls the injection amount to increase during a later fuel injection (fuel injection 813) among multiple fuel injections during the compression stroke, as the environmental temperature (for example, engine water temperature) of the internal combustion engine decreases when the internal combustion engine is started or restarted.

[0096] The fuel injection control device (ECU 150) configured as described above increases the current value of the drive current or the pulse width of the injection pulse during fuel injection (e.g., PL injection) in the later stage of the compression stroke to increase the injection amount. This fuel injection control pushes the mixture in the cylinder 108 from the cavity 606 toward the spark plug 604. As shown on the right side of FIG. 9 , with fuel injection control assuming normal temperatures, a rich mixture 903 does not reach the spark plug 604 during cold start, and the equivalence ratio of the mixture 904 near the end of the combustion chamber 107 decreases. However, with fuel injection control assuming low temperatures, these problems are resolved. As shown in FIG. 11 , a rich mixture 1101 reaches the spark plug 604, and the equivalence ratio of the mixture 1102 near the end of the combustion chamber 107 also increases. Therefore, in this embodiment, ignition retard can be stably performed even when the engine water temperature drops, thereby reducing exhaust emissions during cold start or restart.

[0097] In this embodiment, ignition retard is not performed immediately after starting the engine at extremely low temperatures (for example, below a certain ambient temperature) to avoid engine stall. This is because under these conditions, fuel is not easily vaporized, and the combustion stability required for ignition retard cannot be sufficiently ensured. When a large amount of engine torque is required, such as when accelerating at full throttle during catalyst warm-up, ignition retard control is suspended to avoid engine stall.

[0098] In this embodiment, engine water temperature is used as an example of the engine's environmental temperature. However, the environmental temperature may also be the temperature of the engine's intake air, the temperature of the engine's cylinders 108, or the temperature of the fuel. For example, the fuel temperature may drop significantly immediately after refueling (refueling). When the fuel temperature drops, the fuel viscosity decreases, and the spray penetration decreases. Since the same issues as those during cold start occur immediately after refueling, the lower the fuel temperature, the greater the increase in the current value of the drive current or the pulse width of the injection pulse for fuel injection 806 in the latter part of the compression stroke. By performing the above fuel injection control, sufficient combustion stability can be ensured even immediately after refueling, and ignition retard can be performed.

[0099] In this embodiment, the environmental temperature may be determined comprehensively using two or more of the engine water temperature, the engine intake air temperature, the temperature of the engine cylinders 108, and the fuel temperature. In other words, the environmental temperature may be at least one of the engine water temperature, the engine intake air temperature, the temperature of the engine cylinders 108, and the fuel temperature.

[0100] <Second embodiment> A fuel injection system to which a fuel injection control device according to a second embodiment of the present invention is applied will be described with reference to Figures 12 and 13. The fuel injection control according to the second embodiment differs from the fuel injection control according to the first embodiment in that the lower the engine water temperature, the more frequently fuel is injected by PL injection in the latter part of the compression stroke. The configuration other than the characteristic configuration of this second embodiment is the same as that of the first embodiment, and redundant description will be omitted.

[0101] FIG. 12 is a diagram showing an example of the crank angle, injection timing, and lift amount of the fuel injector (valve element 214) when splitting the PL injection in the latter part of the compression stroke in the second embodiment. As in FIG. 8, in FIG. 12, the horizontal axis represents the crank angle when the top dead center of the intake stroke is −360 degrees ATDC, and the vertical axis represents the lift amount of the fuel injector. The solid line represents fuel injection assumed at room temperature, and the dashed line represents fuel injection assumed at low temperature according to this embodiment. FIG. 12 shows that a second fuel injection by PL injection is performed as a fuel injection in the latter part of the compression stroke, as in fuel injection 1201 performed at timing t121 of compression stroke 802.

[0102] As a specific example of the second embodiment, fuel injection control when performing two PL injections will be described. The fuel injection control during intake stroke 801 is the same as the method of increasing the fuel injection amount of PL injection shown in FIG. 8 , and the lower the engine water temperature, the smaller the injection amount is, as in fuel injections 810 and 811, at timings t81 and t82 of fuel injections 803 and 804. Furthermore, fuel injection control during compression stroke 802 remains unchanged for fuel injection 812 by FL injection, and fuel injection 813′ by PL injection is also performed in the same manner as fuel injection 806 assumed at room temperature. For fuel injection 813′ by PL injection, the injection timing (timing t84) is not changed, but the fuel injection amount is the same as fuel injection 806 assumed at room temperature. Then, fuel injection 1201 is performed at timing t121, which is after timing t83 of fuel injection 812 by FL injection during compression stroke 802 and before timing t84 of fuel injection 813′ by PL injection.

[0103] In this embodiment, it is assumed that the current value of the drive current or the pulse width of the injection pulse in fuel injection 1201, i.e., the fuel injection amount, is the same as that in fuel injection 813', but a penetration force equivalent to that in the case of increasing the penetration force during PL injection (see FIG. 8) is required. Therefore, even if the injection amount division ratio between fuel injection 813' and fuel injection 1201 increases on either side, there is no problem as long as a penetration force equivalent to that in the case of increasing the penetration force during PL injection is obtained. Also, the amount of decrease in the fuel injection amount during intake stroke 801 and the amount of increase in the fuel injection amount during compression stroke 802 can be made equal. This is the same concept as in the first embodiment.

[0104] Next, the analysis results of the in-cylinder air-fuel mixture when the outside air temperature is low in the second embodiment will be described with reference to FIG. Fig. 13 is a diagram showing the in-cylinder equivalence ratio distribution near the ignition timing at low temperatures when fuel injection control according to the second embodiment of the present invention, shown by the dashed line in Fig. 12, is performed. As shown in Fig. 13, even if the engine water temperature drops when the engine is started, by performing fuel injections 810, 811, 812, 1201, and 813' assuming low temperatures, a rich air-fuel mixture 1301 reaches the area around the spark plug 604, and a stratified air-fuel mixture is formed in the combustion chamber 107. In other words, this embodiment can increase the injection amount and improve the penetration of the spray by increasing the number of PL injections, even under conditions where the engine water temperature is low and the penetration of the spray is reduced.

[0105] Therefore, this embodiment can push up the air-fuel mixture formed by FL injection (fuel injection 812) during the compression stroke toward the area around the spark plug 604. In this way, this embodiment can obtain the effect of providing a rich air-fuel mixture around the spark plug 604, similar to the method of increasing the current value of the drive current or the pulse width of the injection pulse during fuel injection in the later part of the compression stroke. Therefore, this embodiment can perform stable ignition retard during cold start by increasing the number of fuel injections by PL injection in the later part of the compression stroke.

[0106] As described above, in this embodiment, two fuel injections 1201, 813' are performed by PL injection during the fuel injection in the latter part of the compression stroke 802, and the timing of the second PL injection (timing t84) is not changed, but a configuration in which this timing is changed is not excluded. That is, the lower the engine water temperature, the more delayed the timing of the second PL injection performed as fuel injection 813' in the latter part of the compression stroke may be, as long as the amount of fuel adhesion does not increase beyond a predetermined amount.

[0107] The present invention is not limited to the above-described embodiments, and various other applications and modifications are possible without departing from the spirit of the present invention as defined in the claims. For example, the above-described embodiments have described the configurations of the fuel injection device and fuel injection system in detail and specifically in order to clearly explain the present invention, and are not necessarily limited to those including all of the components described. Furthermore, it is possible to replace part of the configuration of one embodiment with a component of another embodiment. It is also possible to add a component of another embodiment to the configuration of one embodiment. It is also possible to add, replace, or delete other components from part of the configuration of each embodiment.

[0108] Furthermore, the above-described configurations, functions, processing units, etc. may be partially or entirely realized in hardware, for example, by designing them as integrated circuits, etc. As the hardware, a broad processor device such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) may be used. [Explanation of symbols]

[0109] 1...Fuel injection system, 101...Fuel injection device, 104...CPU, 104M...Memory, 107...Combustion chamber, 108...Cylinder, 150...ECU, 606...Cavity, 609...Piston, 711...Thermostat, 801...Intake stroke, 802...Compression stroke, 803-806...Fuel injection (assumed to be at normal temperature), 810-813, 813', 1201...Fuel injection (assumed to be at low temperature), t81-t85, t121...Timing

Claims

1. A fuel injection control device that controls a fuel injection device that can inject fuel multiple times during one combustion cycle of an internal combustion engine in which an ignition plug ignites an air-fuel mixture, a control unit that, when a first fuel injection among a plurality of fuel injections during a compression stroke is an early fuel injection and second and subsequent fuel injections are late fuel injections, controls the injection amount during the late fuel injection so as to increase as the environmental temperature of the internal combustion engine decreases when the internal combustion engine is started or restarted, the early fuel injection during the compression stroke is a full-lift injection in which the fuel injection valve is displaced to a maximum lift amount, When the penetration force of the spray of the full lift injection in the latter stage during the compression stroke is expected to be higher than a predetermined value, the penetration force of the spray is suppressed by performing a partial lift injection in the latter stage of fuel injection, which does not displace the fuel injection valve to the maximum lift amount, and the spray with suppressed penetration force is controlled so that the air-fuel mixture formed by the full lift injection in the earlier stage is held around the spark plug, When it is assumed that the penetration force of the spray of the later full lift injection during the compression stroke is not higher than a predetermined value, the later fuel injection is performed as a full lift injection, so that the air-fuel mixture formed by the earlier full lift injection is pushed up toward the periphery of the spark plug. Fuel injection control device.

2. the control unit increases a current value of a drive current supplied to the fuel injection device, or a pulse width of a pulse signal for applying a drive voltage to the fuel injection device, or a number of injections, so as to increase an injection amount by the multiple fuel injections in the compression stroke, as the environmental temperature is lower when the internal combustion engine is started or restarted; the control unit reduces a current value of a drive current supplied to the fuel injection device or a pulse width of a pulse signal for applying a drive voltage to the fuel injection device in order to reduce an injection amount of fuel injected during an intake stroke as the environmental temperature decreases when the internal combustion engine is started or restarted, The amount of decrease in the injection amount due to the fuel injection during the intake stroke is made equal to the amount of increase in the injection amount due to the fuel injection during the compression stroke.

2. The fuel injection control device according to claim 1.

3. When increasing the injection amount of the partial lift injection in the fuel injection at the later stage of the compression stroke, the control unit increases the current value of the drive current supplied to the fuel injection device or the pulse width of the pulse signal for applying a drive voltage to the fuel injection device without changing the injection timing depending on the environmental temperature at the time of starting or restarting the internal combustion engine.

3. The fuel injection control device according to claim 2.

4. The control unit increases the number of partial lift injections in the later fuel injection during the compression stroke as the environmental temperature decreases when the internal combustion engine is started or restarted.

3. The fuel injection control device according to claim 2.

5. The environmental temperature is at least one of the temperature of the cooling water that cools the internal combustion engine, the temperature of the intake air of the internal combustion engine, the temperature of the cylinder of the internal combustion engine, and the temperature of the fuel.

2. The fuel injection control device according to claim 1.

6. A fuel injection control method using a fuel injection control device that controls a fuel injection device that can inject fuel multiple times during one combustion cycle of an internal combustion engine in which an ignition plug ignites an air-fuel mixture, comprising: When a first fuel injection among a plurality of fuel injections during a compression stroke is an early fuel injection and second and subsequent fuel injections are late fuel injections, the injection amount is controlled to be increased during the late fuel injection as the environmental temperature of the internal combustion engine decreases when the internal combustion engine is started or restarted, the early fuel injection during the compression stroke is a full-lift injection in which the fuel injection valve is displaced to a maximum lift amount, When the penetration force of the spray of the full lift injection in the latter stage during the compression stroke is expected to be higher than a predetermined value, the penetration force of the spray is suppressed by performing a partial lift injection in the latter stage of fuel injection, which does not displace the fuel injection valve to the maximum lift amount, and the spray with suppressed penetration force is controlled so that the air-fuel mixture formed by the full lift injection in the earlier stage is held around the spark plug, When it is assumed that the penetration force of the spray of the later full lift injection during the compression stroke is not higher than a predetermined value, the later fuel injection is performed as a full lift injection, so that the air-fuel mixture formed by the earlier full lift injection is pushed up toward the periphery of the spark plug. Fuel injection control method.

Images