Injection control device

Abstract

To suppress limitation on the number of injections in multi-stage injection. [Solution] An injection control device 100 includes an injection valve 17 that injects fuel into a combustion chamber of an internal combustion engine, a drive circuit 20 having an on-board battery 21, a boost circuit 22 that boosts the power from the battery, and a current supply circuit 23 that supplies a drive current to the injection valve using the power boosted by the boost circuit, and a control unit that controls the drive circuit. The control unit determines whether a first interval from a first injection time to a second injection time that are successive injection times is equal to or greater than a first threshold value based on the target number of injections and the target injection time, and determines whether a second interval from a second injection time to a third injection time that are successive injection times is equal to or greater than a second threshold value, and corrects the number of injections to be less than the target number of injections when it is determined that the first interval is less than the first threshold value and the second interval is less than the second threshold value.

Description

[Technical field]

[0001] The present invention relates to an injection control device for controlling fuel injection in a direct injection internal combustion engine that performs multi-stage injection. [Background technology]

[0002] In recent years, research and development has been conducted on multi-stage injection for internal combustion engines, which contributes to energy efficiency, in order to ensure access to affordable, reliable, sustainable, and modern energy for all people. As a conventional technology of this type, a device that adjusts the number of injections and the injection interval of multi-stage injection is known (see, for example, Patent Document 1). In the device described in Patent Document 1, the number of injections is set so as to ensure the charging time of the boost capacitor of the high-voltage generation circuit that generates the high voltage applied to the electromagnetic solenoid of the fuel injection valve, and injection later than the injection possible deadline is prohibited. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-106350 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the number of injections is set so as to ensure the charging time of the boost capacitor, as in the device described in Patent Document 1 above, the number of injections in multi-stage injection is limited, which may reduce the effect of multi-stage injection. [Means for solving the problem]

[0005] The injection control device according to one aspect of the present invention includes an injection valve that injects fuel into a combustion chamber of an internal combustion engine, a battery, and a booster that boosts the power from the battery. and charge the capacitor A boost circuit that boosts the The capacitor is chargedThe control unit includes an injection setting unit that sets a target number of injections and a target injection timing per combustion cycle of the internal combustion engine based on an operating condition of the internal combustion engine, and a control unit that sets a first interval from the valve opening timing of the first injection to the valve opening timing of the second injection based on the target number of injections and the target injection timing set by the injection setting unit when the number of injections in a single combustion cycle or the total number of injections in two consecutive combustion cycles is at least three injections is defined as a first injection, a second injection, and a third injection. , which is the charging time after the capacitor is discharged corresponding to the first injection It is determined whether the second interval from the valve opening timing of the second injection to the valve opening timing of the third injection is equal to or greater than the first threshold value. , which is the charging time after the capacitor is discharged corresponding to the second injection. The fuel injection control system includes an interval determination unit that determines whether the first interval is equal to or greater than a second threshold value, and an injection number correction unit that corrects the number of injections per combustion cycle to be less than the target injection number set by the injection setting unit when the interval determination unit determines that the first interval is less than the first threshold value and that the second interval is less than the second threshold value. Effect of the Invention

[0006] According to the present invention, it is possible to suppress limitations on the number of injections in multi-stage injection. [Brief description of the drawings]

[0007] [Figure 1] 1 is a diagram showing a schematic configuration of a main part of an engine to which an injection control device according to an embodiment of the present invention is applied; [Diagram 2] 2 is a diagram showing a schematic configuration of a main part of a drive circuit that drives the injector shown in FIG. 1; [Diagram 3] 1 is a block diagram showing a configuration of a main part of an injection control device according to an embodiment of the present invention; [Figure 4] 2 is a diagram for explaining a temperature rise on the piston crown surface of FIG. 1; FIG. [Diagram 5] FIG. 6 is a diagram showing an example of an injection characteristic map corresponding to an adhesion reduction mode. [Figure 6]FIG. 6 is a diagram for explaining an injection interval in an adhesion reduction mode. [Figure 7] FIG. 6 is a diagram for explaining an injection interval in a knock suppression mode. [Figure 8] 2 is a diagram for explaining a boost recovery time of the capacitor in FIG. 1; [Figure 9] 13 is a diagram for explaining a case where the boosted state of a capacitor does not recover. [Figure 10] 13A and 13B are diagrams for explaining a case where the boosted state of a capacitor is restored. [Figure 11] FIG. 11 is a diagram for explaining modified examples of the first injection, the second injection, and the third injection. [Figure 12] 4 is a flowchart showing an example of a process performed by an injection control device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to Fig. 1 to Fig. 12. An injection control device according to an embodiment of the present invention is applied to a direct injection internal combustion engine that performs multi-stage injection. In particular, an example in which the injection control device is applied to a direct injection gasoline engine mounted on a vehicle will be described below.

[0009] Fig. 1 is a diagram that shows a schematic configuration of a main part of an engine 1 to which an injection control device according to an embodiment of the present invention is applied. The engine 1 is a spark-ignition internal combustion engine, and is a four-stroke engine that undergoes four strokes during one combustion cycle: an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. The engine 1 has multiple cylinders, such as four cylinders, but Fig. 1 shows the configuration of a single cylinder. Note that the configuration of each cylinder is the same as each other.

[0010] As shown in Fig. 1, the engine 1 has a cylinder 2a formed in a cylinder block 2, a piston 3 slidably disposed inside the cylinder 2a, and a combustion chamber 5 formed between a crown surface (piston crown surface) 3a of the piston 3 and a cylinder head 4. A recess 3b is formed in the piston crown surface 3a so as to follow, for example, a tumble flow in the cylinder. The piston 3 is connected to a crankshaft 7 via a connecting rod 6, and the crankshaft 7 rotates as the piston 3 reciprocates along the inner wall of the cylinder 2a.

[0011] The cylinder head 4 is provided with an intake port 8 and an exhaust port 9. An intake passage 10 communicates with the combustion chamber 5 via the intake port 8, and an exhaust passage 11 communicates with the combustion chamber 5 via the exhaust port 9. The intake port 8 is opened and closed by an intake valve 12, and the exhaust port 9 is opened and closed by an exhaust valve 13. A throttle valve 14 is provided in the intake passage 10 upstream of the intake valve 12. The throttle valve 14 is formed of, for example, a butterfly valve, and adjusts the amount of intake air to the combustion chamber 5. The intake valve 12 and the exhaust valve 13 are driven to open and close by a valve mechanism 15.

[0012] An ignition plug 16 and a direct injection type injector 17 are attached to the cylinder head 4 so as to face the combustion chamber 5. The ignition plug 16 is disposed between the intake port 8 and the exhaust port 9, and generates a spark using electrical energy to ignite the mixture of fuel and air in the combustion chamber 5.

[0013] The injector 17 is disposed near the intake valve 12 and is driven by electrical energy to inject fuel. More specifically, high-pressure fuel is supplied to the injector 17 from a fuel tank via a fuel pump. The injector 17 atomizes the fuel and injects the fuel diagonally downward into the combustion chamber 5 at a predetermined timing. The location of the injector 17 is not limited to this, and it may be disposed near the spark plug 16, for example.

[0014] The valve train 15 has an intake camshaft 18 and an exhaust camshaft 19. The intake camshaft 18 has an intake cam 18a that corresponds to each cylinder (cylinder 2a) and the exhaust camshaft 19 has an exhaust cam 19a that corresponds to each cylinder. The intake camshaft 18 and the exhaust camshaft 19 are connected to the crankshaft 7 via a timing belt (not shown) and each rotates once for every two rotations of the crankshaft 7.

[0015] The intake valve 12 opens and closes at a predetermined timing according to the profile of an intake cam 18a via an intake rocker arm (not shown) as the intake camshaft 18 rotates. The exhaust valve 13 opens and closes at a predetermined timing according to the profile of an exhaust cam 19a via an exhaust rocker arm (not shown) as the exhaust camshaft 19 rotates.

[0016] FIG. 2 is a diagram showing a schematic configuration of a main part of a drive circuit 20 that drives the injector 17. FIG. 2 shows an example in which the engine 1 is an in-line four-cylinder engine. In this engine 1, ignition occurs every time the crank angle increases by 180° in the order of the first cylinder #1, the third cylinder #3, the fourth cylinder #4, and the second cylinder #2. In the following, it is assumed that the injector 17a injects fuel into the combustion chamber 5a of the first cylinder #1, the injector 17b injects fuel into the combustion chamber 5b of the third cylinder #3, the injector 17c injects fuel into the combustion chamber 5c of the fourth cylinder #4, and the injector 17d injects fuel into the combustion chamber 5d of the second cylinder #2.

[0017] 2, the drive circuit 20 has a single boost circuit 22 that boosts the power (voltage) from the vehicle-mounted battery 21, and a current supply circuit 23 that supplies drive currents to the injectors 17a to 17d using the power boosted by the boost circuit 22. The boost circuit 22 has a single capacitor 22a. By sharing the single boost circuit 22 having the single capacitor 22a in this way among the four injectors 17a to 17d, it is possible to reduce the number of parts, hold down costs, and simplify the configuration.

[0018] The boost circuit 22 includes a capacitor 22a, a boost coil 22b, a FET 22c as a switching element, a diode as a rectifying element, a resistor, etc. One end of the boost coil 22b is connected to the vehicle battery 21, and the other end of the boost coil 22b is connected to the drain of the FET 22c and to the capacitor 22a via the diode. The source of the FET 22c is connected to the resistor.

[0019] When a switching signal is input to the gate of FET 22c and FET 22c is turned on, the battery voltage is applied to boost coil 22b and electrical energy is stored. When a switching signal is input to the gate of FET 22c and FET 22c is turned off, the electrical energy stored in boost coil 22b is supplied to and stored in capacitor 22a. By repeatedly turning FET 22c on and off, the battery voltage is boosted up to a predetermined boost voltage corresponding to the capacitance of capacitor 22a.

[0020] The current supply circuit 23 has FETs 23a, 23b, and 23c as switching elements, and diodes, resistors, and the like as rectifying elements. The source of the FET 23a is connected to the output side of the boost circuit 22, and the drain of the FET 23a is connected to one end of the solenoid actuator of each of the injectors 17a to 17d. The source of the FET 23b is directly connected to the vehicle battery 21, and the drain of the FET 23b is connected to one end of the solenoid actuator of each of the injectors 17a to 17d via a diode. The drain of the FET 23c is connected to the other end of the solenoid actuator of each of the injectors 17a to 17d. A diode is interposed between the gate and drain of the FET 23c, and a resistor is interposed between the gate and source of the FET 23c.

[0021] When each of the injectors 17a to 17d is opened from a closed state, a switching signal is input to the gate of the FET 23a and FET 23c corresponding to each of the injectors 17a to 17d, and the FET 23a and FET 23c are turned on. This causes the capacitor 22a of the boost circuit 22 to discharge, and the boosted voltage is applied to the solenoid actuator of each of the injectors 17a to 17d, thereby opening each of the injectors 17a to 17d from a closed state.

[0022] To maintain the open state of each of the injectors 17a to 17d after opening them, a switching signal is input to the gates of the FETs 23a and 23b corresponding to each of the injectors 17a to 17d, turning off the FET 23a and turning on the FET 23b. As a result, the battery voltage from the vehicle-mounted battery 21 is applied to the solenoid actuators of each of the injectors 17a to 17d instead of the boosted voltage from the boost circuit 22, and the open state of each of the injectors 17a to 17d is maintained.

[0023] When each of the injectors 17a to 17d is closed from an open state, a switching signal is input to the gate of the FET 23b and FET 23c corresponding to each of the injectors 17a to 17d, and the FET 23b and FET 23c are turned off. This stops the supply of drive current to the solenoid actuator of each of the injectors 17a to 17d, and each of the injectors 17a to 17d is closed from an open state.

[0024] Fig. 3 is a block diagram showing the configuration of the main parts of an injection control device (hereinafter, referred to as device) 100 according to an embodiment of the present invention. As shown in Fig. 3, the device 100 is mainly configured with a controller 30. A crank angle sensor 31, an accelerator opening sensor 32, a water temperature sensor 33, an intake amount sensor 34, an AF sensor 35, a fuel pressure sensor 36, a fuel temperature sensor 37, and a drive circuit 20 are connected to the controller 30.

[0025] The crank angle sensor 31 is provided on the crankshaft 7 (FIG. 1) and configured to output a pulse signal in accordance with the rotation of the crankshaft 7. Based on the pulse signal from the crank angle sensor 31, the controller 30 determines the rotation angle (crank angle) of the crankshaft 7 based on the position of top dead center TDC when the piston 3 starts the intake stroke, and calculates the engine speed.

[0026] The accelerator opening sensor 32 is provided on an accelerator pedal of the vehicle equipped with the engine 1, and detects the amount of accelerator pedal operation (accelerator opening). A target torque of the engine 1 is commanded according to the detection value of the accelerator opening sensor 32. The water temperature sensor 33 is provided in a path through which engine coolant flows to cool the engine 1, and detects the temperature of the engine coolant (coolant temperature). The intake amount sensor 34 is a sensor that detects the amount of intake air, and is constituted by, for example, an air flow meter disposed in the intake passage 10 (more specifically, upstream of the throttle valve). The AF sensor 35 is provided in the exhaust passage 11, and detects the air-fuel ratio of the exhaust gas in the exhaust passage 11.

[0027] The fuel pressure sensor 36 detects the pressure of the high-pressure fuel supplied to the injector 17 via the fuel pump. The fuel temperature sensor 37 is a sensor that detects the temperature of the fuel supplied to the injector 17, and is provided, for example, in the fuel pipe.

[0028] The controller 30 executes a predetermined process based on signals from the sensors 31-37, and outputs switching signals to the FETs 22c, 23a-23c, thereby controlling the drive circuit 20. More specifically, the controller 30 controls the drive circuit 20 so that after the injector 17a injects fuel into the combustion chamber 5a, the injector 17b injects fuel into the combustion chamber 5b, after the injector 17b injects fuel into the combustion chamber 5b, the injector 17c injects fuel into the combustion chamber 5c, after the injector 17c injects fuel into the combustion chamber 5c, the injector 17d injects fuel into the combustion chamber 5d, and after the injector 17d injects fuel into the combustion chamber 5d, the injector 17a injects fuel into the combustion chamber 5a.

[0029] The controller 30 is configured by an electronic control unit (ECU) including a computer having a calculation unit such as a CPU, a storage unit such as a ROM and a RAM, and other peripheral circuits. The controller 30 has, as functional components, a temperature range determination unit 301, an injection setting unit 302, an interval determination unit 303, and an injection number correction unit 304.

[0030] The temperature range determination unit 301 determines whether the engine 1 is in a low in-cylinder temperature state where the temperature Tp of the piston crown surface 3a (FIG. 1) is less than a predetermined temperature Tp0 (e.g., 100°C) or in a high in-cylinder temperature state where the temperature Tp is equal to or higher than the predetermined temperature Tp0, based on the workload of the engine 1. In the case of a gasoline engine, the output (power) of the engine 1 correlates with the intake air amount G, and the workload (total workload) of the engine 1 correlates with the integrated amount ΣG of the intake air amount G. The cylinder 2a and piston 3 that constitute the combustion chamber 5 each have a heat capacity according to their material and mass, so that a certain amount of heat, i.e., a certain amount of workload, is required to raise the temperatures of these components.

[0031] Fig. 4 is a diagram for explaining the temperature rise of the piston crown surface 3a, and shows an example of the change over time in the amount of soot emission measured by a measuring device when the engine 1 is warmed up from a cold state. The temperature Tp of the piston crown surface 3a shown in Fig. 4 is an estimated value, and the cooling water temperature Tw is a detection value of the water temperature sensor 33. Moreover, the integrated amount ΣG of the intake air amount G is a calculated value calculated based on the intake air amount G detected by the intake air amount sensor 34.

[0032] As shown in FIG. 4, when the engine 1 is in a cold state, the temperature of the entire engine 1 including the piston crown surface 3a and the engine coolant is uniform, and the cold state of the engine 1 can be detected by the water temperature sensor 33 as the coolant temperature Tw at the start of the engine 1. When the engine 1 is warming up, the integrated amount ΣG (amount of heat generated by combustion, amount of work) of the intake air amount G increases, and the temperature Tp of the piston crown surface 3a rises. When the temperature Tp of the piston crown surface 3a rises, the entire engine 1 including the piston crown surface 3a is gradually warmed up from the combustion chamber 5 side, and the coolant temperature Tw rises. When the engine 1 is warmed up, the engine coolant passes through a radiator (not shown) to maintain the coolant temperature Tw at or below a predetermined temperature Tw0 (for example, 90° C.), and the engine 1 is cooled by the engine coolant.

[0033] As shown in Fig. 4, the amount of soot emission is generally constant until time t0, at which point it drops sharply and falls below the target emission amount. To explain this point, as shown in Fig. 1, the fuel injected from the injector 17 adheres to the piston crown surface 3a (recess 3b). At this time, if the temperature Tp of the piston crown surface 3a reaches a predetermined temperature Tp0 (e.g., 100°C), the adhered fuel immediately evaporates, and soot is unlikely to be generated. On the other hand, if the temperature Tp of the piston crown surface 3a does not reach the predetermined temperature Tp0, the adhered fuel is incompletely combusted, and soot is likely to be generated.

[0034] 4, it is possible to previously grasp the integrated amount (threshold value) ΣG0 of the intake air amount G required for the temperature Tp of the piston crown surface 3a to reach a predetermined temperature Tp0 from the cooling water temperature Tw at the start of the engine 1. When the integrated amount ΣG of the intake air amount G is less than the threshold value ΣG0, the temperature range determination unit 301 determines that the engine 1 is in a low in-cylinder temperature state, and when it is equal to or greater than the threshold value ΣG0, the temperature range determination unit 301 determines that the engine 1 is in a high in-cylinder temperature state. This makes it possible to determine whether the temperature Tp of the piston crown surface 3a, which reciprocates in the cylinder 2a facing the high-temperature combustion chamber 5, has reached the predetermined temperature Tp0 without directly detecting the temperature Tp of the piston crown surface 3a by a sensor.

[0035] 4 differs depending on the cold state of the engine 1, i.e., depending on the coolant temperature Tw at the time of startup. That is, the threshold ΣG0 of the integrated amount ΣG of the intake air amount G required for the engine 1 to reach a high in-cylinder temperature state is larger as the coolant temperature Tw at the time of startup of the engine 1 is lower, and is smaller as the coolant temperature Tw is higher. The characteristics of the threshold ΣG0 with respect to the coolant temperature Tw at the time of startup of the engine 1 are stored in advance in a memory.

[0036] The injection setting unit 302 in FIG. 3 sets a target number of injections and a target injection timing per combustion cycle of the engine 1 based on characteristics that are determined in advance according to the operating conditions of the engine 1.

[0037] <Adhesion reduction mode> When the temperature range determination unit 301 determines that the engine 1 is in a low cylinder temperature state, the injection setting unit 302 sets the target number of injections and the target injection timing so as to suppress the adhesion of fuel to the piston crown surface 3a, the inner wall surface of the cylinder 2a, etc. (adhesion reduction mode). In the adhesion reduction mode, fuel is injected and a mixture is generated in a region other than a predetermined injection prohibition region near the intake top dead center TDC at the start of the intake stroke and the compression top dead center TDC at the end of the compression stroke, that is, in a region (injection possible region) where the piston crown surface 3a is separated from the injector 17. At this time, the amount of fuel injected per injection is suppressed by injecting fuel in multiple stages. As a result, it is possible to suppress the adhesion of fuel to the piston crown surface 3a and the wall surface of the cylinder 2a, and to suppress the generation of soot. The injection prohibition region is set, for example, to a part or almost the entire region of the first half of the intake stroke and a part or almost the entire region of the second half of the compression stroke.

[0038] More specifically, the injection prohibition region is set according to the engine speed. The higher the engine speed, the faster the piston crown surface 3a retreats from the injector 17 during the intake stroke and the faster the piston crown surface 3a approaches the injector 17 during the compression stroke. Therefore, the higher the engine speed, the narrower the injection prohibition region during the intake stroke (the end of the injection prohibition region moves toward the advance side) and the wider the injection prohibition region during the compression stroke (the start of the injection prohibition region moves toward the advance side).

[0039] The target number of injections and the target injection timing in the injection possible region are determined by an injection specific map stored in advance in a memory, for example, a characteristic map shown in FIG. 5. That is, as shown in FIG. 5, the target number of injections and the target injection timing are determined by a predetermined characteristic map in association with a characteristic f of the maximum output torque according to the engine speed Ne and the target injection amount Q. When the number of injections is multiple, the injection amounts per injection are equal to each other. The target injection amount Q is calculated as a value that makes the actual air-fuel ratio the target air-fuel ratio, and is determined according to the intake air amount G. Therefore, the injection characteristic map in FIG. 5 can be rewritten as a map of the engine speed Ne and the intake air amount G.

[0040] In Fig. 5, the crank angle from the start of the intake stroke (intake top dead center TDC) to the end of the compression stroke (compression top dead center TDC) is shown by the angle of a clockwise circle starting from intake top dead center TDC, and the timing of fuel injection is shown by sector-shaped hatching extending radially from the center of the circle. The intake stroke is the crank angle range of 0° to 180°, and the compression stroke is the crank angle range of 180° to 360°. The crank angle range of 0° to 90° is sometimes called the first half of the intake stroke, the range of 90° to 180° is sometimes called the second half of the intake stroke, the range of 180° to 270° is sometimes called the first half of the compression stroke, and the range of 270° to 360° is sometimes called the second half of the compression stroke.

[0041] In order to prevent the adhesion of fuel to the piston crown surface 3a, it is preferable to increase the number of injections and reduce the amount of fuel injected per injection. However, the minimum injection amount Qmin per injection of the injector 17 is determined by the specifications of the injector 17, and the injector 17 cannot inject an amount less than the minimum injection amount Qmin (minimum injection time constraint). Therefore, the target number of injections is set to be smaller as the target injection amount Q is smaller.

[0042] In addition, a minimum pause time from valve closing to valve opening of the injector 17 is regulated by the specifications of the injector 17 (minimum pause time constraint). The minimum pause time is set so that the change in the injection amount (flow rate) due to the residual magnetism effect on the solenoid actuator of each of the injectors 17a to 17d (FIG. 2) falls within an allowable range.

[0043] On the other hand, in order to increase the number of injections, it is necessary to drive the injector 17 at high speed, and it is necessary to repeatedly charge and discharge the capacitor 22a in the drive circuit 20 (FIG. 2) in a short time. In this case, the higher the engine speed Ne, the faster the drive speed of the injector 17 needs to be, and the electrical load of the controller 30 that outputs a switching signal to the FET 22c of the drive circuit 20 increases, and the amount of heat generated by the controller 30 increases. As a result, the number of injections is limited by the thermal constraints of the controller 30 (maximum injection number constraint). Therefore, the target number of injections is set to be smaller as the engine speed Ne increases.

[0044] <Knock suppression mode> When the temperature range determination unit 301 determines that the engine 1 is in a high in-cylinder temperature state, if a predetermined knock suppression condition is satisfied, the injection setting unit 302 sets a target number of injections and a target injection timing so as to suppress the occurrence of knocking (knock suppression mode). The knock suppression condition is satisfied when the amount of retardation of the ignition timing required to suppress the occurrence of knocking at low revolutions and high load is equal to or greater than a predetermined value.

[0045] In the knock suppression mode, the retarded ignition timing is returned to the optimal ignition timing side, and fuel is injected once during the intake stroke (e.g., the first half of the intake stroke) and once during the compression stroke (e.g., the first half of the compression stroke) (intake pressure two-stage injection). In this case, the injection amount during the compression stroke is the minimum injection amount Qmin, and the amount obtained by subtracting the minimum injection amount Qmin from the target injection amount Q is injected during the intake stroke. By injecting fuel during the compression stroke, the end gas temperature of the combustion chamber 5 is reduced by the latent heat of vaporization. This makes it possible to suppress the occurrence of knocking while suppressing the amount of retardation of the ignition timing. Therefore, it is possible to improve combustion efficiency compared to the case where fuel is injected only during the intake stroke by retarding the ignition timing.

[0046] 6 is a diagram for explaining the injection interval Δt in the adhesion reduction mode, and shows the injection interval Δt when the injector 17a injects fuel into the combustion chamber 5a of the first cylinder #1 and then the injector 17b injects fuel into the combustion chamber 5b of the third cylinder #3. The injection interval Δt is the time between two successive injections in a single combustion cycle or two successive combustion cycles, and is the time from the valve opening timing of the previous injection (target injection timing) to the valve opening timing of the next fuel injection.

[0047] 6, in the adhesion reduction mode in which multiple injections are performed, the injection interval Δt1 from the final injection (fourth injection in the illustrated example) in the first cylinder #1 to the first injection in the third cylinder #3 may be shorter than the injection interval Δt2 from the first injection to the second injection in the third cylinder #3. That is, in the adhesion reduction mode, the injection intervals in a single combustion cycle in the same cylinder are equal to each other, but the injection interval from the final injection in the previous combustion cycle to the first injection in the next combustion cycle in two consecutive combustion cycles between cylinders may be shorter than the injection interval in the same cylinder.

[0048] Fig. 7 is a diagram for explaining the injection interval Δt in the knock suppression mode. As shown in Fig. 7, even in the knock suppression mode in which injections are performed in the intake stroke and the compression stroke, the injection interval Δt1 from the final injection (e.g., in the first half of the intake stroke) of the first cylinder #1 to the first injection (e.g., in the first half of the compression stroke) of the third cylinder #3 may be shorter than the injection interval Δt2 from the first injection to the second injection of the third cylinder #3. That is, even in the knock suppression mode, the injection interval from the final injection of the previous combustion cycle to the first injection of the next combustion cycle of two consecutive combustion cycles between cylinders may be shorter than the injection interval within the same cylinder.

[0049] FIG. 8 is a diagram for explaining the boost recovery time of the capacitor 22a (FIG. 2). As shown in FIG. 8, after the capacitor 22a is discharged, a predetermined boost recovery time is required until the boosted state in which the voltage is boosted to the boost voltage is restored. More specifically, a predetermined first recovery time Δta is required from opening (discharging) one injector 17 (solenoid actuator) in the boosted state until the boosted state is restored. The first recovery time Δta is determined by the specifications of the injector 17 and the drive circuit 20. After the previous discharge, a predetermined second recovery time Δtb longer than the first recovery time Δta is required from performing the next discharge in a state in which the boosted state has not been restored until the boosted state is restored. The second recovery time Δtb is longest when the previous discharge and the next discharge are performed simultaneously, and in this case, the second recovery time Δtb is about twice the first recovery time Δta.

[0050] 6 and 7, when the injection interval Δt1 is short, particularly at high speed and high load, the injection interval Δt1 falls short of the first return time Δta, and the charge of the capacitor 22a becomes insufficient, which may cause the valve opening of the injector 17 to be delayed or insufficient. In such a case, if the number of injections is reduced so that all injection intervals Δt are equal to or longer than the first return time Δta, the effects of the multi-stage injection, such as reducing adhesion of fuel to the piston crown surface 3a and the inner wall surface of the cylinder 2a, and suppressing knocking, may be lost. Therefore, in this embodiment, the device 100 is configured as follows to prevent the number of injections of the multi-stage injection from being limited.

[0051] FIG. 9 is a diagram for explaining a case where the boosted state of the capacitor 22a does not recover, and shows the injection interval Δt between the first injection, the second injection, and the third injection successively performed by the injector 17, and the charging state of the capacitor 22a. As shown in FIG. 9, when the injection interval Δt1 between the first injection and the second injection is shorter than the first return time Δta, and the injection interval Δt2 between the second injection and the third injection is shorter than the second return time Δtb, the voltage drop of the capacitor 22a accumulates. Such an accumulation of the voltage drop of the capacitor 22a leads to a significant decrease in the injection amount (flow rate) of the injector 17, and is therefore unacceptable. Therefore, it is necessary to ensure an appropriate injection amount by the injector 17 by reducing the number of injections per combustion cycle. In this case, it is necessary to reduce the number of injections by, for example, prohibiting the final injection in each combustion cycle, and to review the injection amount per injection so as to ensure the target injection amount Q.

[0052] FIG. 10 is a diagram for explaining a case where the boosted state of the capacitor 22a is restored. As shown in FIG. 10, even if the injection interval Δt1 between the first injection and the second injection is shorter than the first return time Δta, if the injection interval Δt2 between the second injection and the third injection is equal to or longer than the second return time Δtb, the voltage drop of the capacitor 22a does not accumulate and the boosted state is restored. Since such a temporary voltage drop of the capacitor 22a only limits the reduction in the injection amount by the injector 17, even if the number of injections is maintained, the reduction in combustion performance and emission performance due to the reduction in injection amount may be within an acceptable range. For example, when the previous discharge and the next discharge are performed simultaneously, the operating conditions under which the reduction in combustion performance and emission performance due to the reduction in injection amount is within an acceptable range can be determined in advance by testing.

[0053] Fig. 11 is a diagram for explaining a modified example of the first injection, the second injection, and the third injection, and shows the injection interval Δt when performing two-stage injection. As shown in Fig. 11, the first and second (final) injections of a previous combustion cycle of two consecutive combustion cycles may be the first injection and the second injection, and the first injection of the next combustion cycle may be the third injection. In this case, the previous combustion cycle and the next combustion cycle may be two consecutive combustion cycles in the same cylinder, or may be two consecutive combustion cycles between different cylinders.

[0054] 3 determines whether the injection interval Δt1 between the first injection and the second injection is equal to or longer than the first return time Δta, based on the target number of injections and the target injection timing set by the injection setting unit 302. Then, when it is determined that the injection interval Δt1 is shorter than the first return time Δta, it further determines whether the injection interval Δt2 between the second injection and the third injection is equal to or longer than the second return time Δtb. The second return time Δtb may be predetermined as, for example, a value approximately twice the first return time Δta, or may be calculated according to the injection interval Δt1 between the first injection and the second injection.

[0055] When the interval determination unit 303 determines that the injection interval Δt2 from the second injection to the third injection is less than the second return time Δtb, the injection number correction unit 304 corrects the injection number per combustion cycle to be less than the target injection number. That is, even if the injection interval Δt1 from the first injection to the second injection is less than the first return time Δta, the target injection number is maintained as long as the injection interval Δt2 from the second injection to the third injection is equal to or greater than the second return time Δtb. This makes it possible to prevent the injection number of multi-stage injections from being limited, and to improve emission performance and combustion performance even at relatively high rotation speeds and high loads.

[0056] The controller 30 calculates a target injection amount Q per combustion cycle according to the intake air amount detected by the intake air amount sensor 34 while performing feedback control so that the actual air-fuel ratio detected by the AF sensor 35 becomes the target air-fuel ratio (for example, the theoretical air-fuel ratio). Then, the controller 30 calculates a target injection amount (unit target injection amount) per injection of the injector 17 according to the target injection number set by the injection setting unit 302. More specifically, in the adhesion reduction mode, a value obtained by dividing the target injection amount Q by the target injection number is calculated as the unit target injection amount, and in the knock suppression mode, an amount obtained by subtracting the minimum injection amount Qmin from the minimum injection amount Qmin (compression stroke) and the target injection amount Q is calculated as the target injection amount. The controller 30 controls the drive circuit 20 according to the crank angle θ detected by the crank angle sensor 31 so that the injector 17 injects the unit target injection amount of fuel at the target injection timing. That is, the controller 30 controls the drive circuit 20 by outputting a switching signal to the FETs 22c, 23a to 23c of the drive circuit 20.

[0057] 12 is a flowchart showing an example of processing by the device 100, which is executed by the controller 30 in accordance with a program stored in advance in the memory. The processing shown in this flowchart is started, for example, when the engine 1 starts operating, and is repeated at a predetermined interval.

[0058] As shown in Fig. 12, first, in step S1, signals from the sensors 31-37 are read. Next, in step S2, a target number of injections per combustion cycle from the injector 17 and a target injection timing are set based on the signal read in step S1. Next, in step S3, it is determined whether the target number of injections set in step S2 is multiple, i.e., whether it is a multi-stage injection. If the result in step S3 is affirmative, the process proceeds to step S4, and if the result is negative, the process proceeds to step S8.

[0059] In step S4, it is determined whether or not the injection interval Δt1 between the first injection and the second injection is equal to or longer than the first return time Δta, based on the target number of injections and the target injection timing set in step S2. If the result in step S4 is negative, the process proceeds to step S5, and if the result is positive, the process proceeds to step S8. In step S5, it is determined whether or not the injection interval Δt2 between the second injection and the third injection is equal to or longer than the second return time Δtb, based on the target number of injections and the target injection timing set in step S2. If the result in step S5 is positive, the process proceeds to step S6, and if the result is negative, the process proceeds to step S7.

[0060] In step S6, it is determined based on the signal read in step S1 whether the current operating conditions of the engine 1 are operating conditions in which the deterioration of combustion performance and emission performance due to a decrease in the injection amount is within an acceptable range. If the answer is YES in step S6, the process proceeds to step S8, and if the answer is NO, the process proceeds to step S7. In step S7, the number of injections is decreased by one, and the process returns to step S3. In step S8, a target injection amount and a unit target injection amount are calculated based on the signal read in step S1 and the number of injections set and corrected in steps S2 to S7, and a switching signal is output to the FETs 22c, 23a to 23c of the drive circuit 20 so that the injector 17 injects the unit target injection amount of fuel at the target injection timing.

[0061] According to this embodiment, the following advantageous effects can be obtained. (1) The device 100 includes an injector 17 that injects fuel into a combustion chamber 5 of the engine 1, a drive circuit 20 that has an on-board battery 21, a boost circuit 22 that boosts the power from the on-board battery 21, and a current supply circuit 23 that supplies a drive current to the injector 17 using the power boosted by the boost circuit 22, and a controller 30 that controls the drive circuit 20 (Figures 1 to 3).

[0062] The controller 30 includes an injection setting unit 302 that sets a target number of injections and a target injection timing per combustion cycle of the engine 1 based on the operating conditions of the engine 1, and a control unit 303 that controls the injection interval Δt1 from the valve opening timing of the first injection to the valve opening timing of the second injection based on the target number of injections and the target injection timing set by the injection setting unit 302 when the number of injections in a single combustion cycle or the total number of injections in two consecutive combustion cycles is at least three is defined as a first injection, a second injection, and a third injection. The system has an interval determination unit 303 which determines whether the first interval Δt1 is shorter than the first return time Δta and determines whether the injection interval Δt2 from the valve opening timing of the second injection to the valve opening timing of the third injection is longer than the second return time Δtb, and an injection number correction unit 304 which corrects the number of injections per combustion cycle to be less than the target injection number set by the injection setting unit 302 when the interval determination unit 303 determines that the first interval Δt1 is shorter than the first return time Δta and that the injection interval Δt2 is shorter than the second return time Δtb (FIGS. 3 and 12).

[0063] That is, even if the injection interval Δt1 between the first and second injections is less than the first return time Δta, the target number of injections is maintained as long as the injection interval Δt2 between the second and third injections is equal to or greater than the second return time Δtb (Fig. 10). This makes it possible to prevent the number of injections in multi-stage injection from being restricted, and improves emission and combustion performance even at relatively high speeds and high loads.

[0064] (2) The combustion chamber 5 includes combustion chambers 5a and 5b, and the injector 17 includes injectors 17a and 17b that inject fuel into the combustion chambers 5a and 5b, respectively (FIG. 2). The current supply circuit 23 supplies drive currents to the injectors 17a and 17b, respectively, and the controller 30 controls the drive circuit 20 so that after the injector 17a injects fuel into the combustion chamber 5a, the injector 17b injects fuel into the combustion chamber 5b. The first injection is the final injection of the combustion cycle by the injector 17a, the second injection is the first injection of the combustion cycle by the injector 17b, and the third injection is the second injection of the combustion cycle by the injector 17b (FIGS. 6 to 10).

[0065] That is, when multi-stage injection is performed in a multi-cylinder engine, especially at high speed and high load, the injection interval between the final injection of the previous combustion cycle and the first injection of the next combustion cycle among two consecutive combustion cycles between cylinders becomes short and may fall short of the specified boost recovery time. Even in such a case, if the injection interval between the first injection and the second injection of the next combustion cycle is sufficiently long, the number of injections can be maintained to improve the emission performance and combustion performance even at relatively high speed and high load.

[0066] (3) The controller 30 further includes a temperature range determination unit 301 that determines whether the engine 1 is in a low in-cylinder temperature state where the temperature Tp of the piston crown surface 3a is less than a predetermined temperature Tp0 or in a high in-cylinder temperature state where the temperature Tp is equal to or higher than the predetermined temperature Tp0 (FIG. 3). When the temperature range determination unit 301 determines that the engine 1 is in a low in-cylinder temperature state, the injection setting unit 302 sets a target number of injections and a target injection timing so that fuel is injected multiple times from the intake stroke to the compression stroke of the combustion cycle (FIG. 6). That is, in the adhesion reduction mode, adhesion of fuel to the piston crown surface 3a, the inner wall surface of the cylinder 2a, etc. is suppressed by performing multiple injections, thereby suppressing the generation of soot and improving emission performance.

[0067] (4) The controller 30 further includes a temperature range determination unit 301 that determines whether the engine 1 is in a low in-cylinder temperature state where the temperature Tp of the piston crown surface 3a is less than a predetermined temperature Tp0 or in a high in-cylinder temperature state where the temperature Tp is equal to or higher than the predetermined temperature Tp0 (FIG. 3). When the temperature range determination unit 301 determines that the engine 1 is in a high in-cylinder temperature state, the injection setting unit 302 sets a target number of injections and a target injection timing so that fuel is injected once in each of the intake stroke and the compression stroke of the combustion cycle if a predetermined knock suppression condition is established (FIG. 7). That is, in the knock suppression mode, the intake pressure two-stage injection is performed to reduce the end gas temperature of the combustion chamber 5 by the vaporization latent heat of the fuel injected in the compression stroke, thereby suppressing the occurrence of knocking while suppressing the amount of retardation of the ignition timing, and improving the combustion performance.

[0068] (5) The boost circuit 22 has a single capacitor 22a (FIG. 2). By sharing the single boost circuit 22 having the single capacitor 22a among the multiple injectors 17a to 17d, it is possible to reduce the number of parts, hold down costs, and simplify the configuration.

[0069] In the above embodiment, an example in which the present invention is applied to an on-vehicle gasoline engine has been described, but the present invention can also be applied to internal combustion engines other than on-vehicle engines and internal combustion engines other than gasoline engines. Also, while a specific configuration of the injector 17 has been described as an example in Figure 1 etc., the configuration of the injection valve that injects fuel into the combustion chamber is not limited to the example.

[0070] In the above embodiment, the target number of injections and the target injection timing in the adhesion reduction mode are determined according to the characteristics map in Fig. 5 etc., which shows the relationship between the engine speed and the target injection amount determined according to the intake air amount detected by the intake air amount sensor 34. That is, the engine output torque is detected based on the signal from the intake air amount sensor 34. However, the injection setting unit, which sets the target number of injections per combustion cycle and the target injection timing based on the operating conditions of the internal combustion engine, may be configured to use other physical quantities that are correlated with the engine output torque.

[0071] In the above embodiment, the temperature range determination unit 301 uses the integrated amount of intake air as the workload of the engine 1 to determine whether the engine 1 is in a low or high in-cylinder temperature state, but the temperature range determination unit that determines whether the temperature of the combustion chamber is equal to or higher than a predetermined temperature is not limited to this. For example, the integrated amount of fuel injection may be used as the workload of the internal combustion engine. Also, although the temperature of the piston crown surface 3a is estimated as the in-cylinder temperature, the temperature of the cylinder wall surface or the rotor surface of a rotary engine may be estimated.

[0072] In the above embodiment, an example has been described in which the interval determination unit 303 determines whether the injection interval Δt1 from the first injection to the second injection is equal to or longer than the first return time Δta in step S4 of Fig. 12, and if the determination is negative, the process proceeds to step S5 to determine whether the injection interval Δt2 from the second injection to the third injection is equal to or longer than the second return time Δtb, but the interval determination unit that determines whether the first interval is equal to or longer than the first threshold value and determines whether the second interval is equal to or longer than the second threshold value is not limited to this. For example, the determination of whether the injection interval Δt1 is equal to or longer than the first return time Δta and the determination of whether the injection interval Δt2 is equal to or longer than the second return time Δtb may be performed in parallel, or the determination of whether the injection interval Δt2 is equal to or longer than the second return time Δtb may be performed first, and then the determination of whether the injection interval Δt1 is equal to or longer than the first return time Δta may be performed.

[0073] The above description is merely an example, and the present invention is not limited to the above-mentioned embodiment and modifications, as long as the features of the present invention are not impaired. The above-mentioned embodiment and one or more modifications can be arbitrarily combined, and modifications can be combined with each other. [Explanation of symbols]

[0074] 1 engine, 2 cylinder, 3 piston, 3a piston crown surface, 5, 5a to 5d combustion chamber, 17, 17a to 17d injector, 20 drive circuit, 21 vehicle battery, 22 boost circuit, 22a capacitor, 22b boost coil, 22c FET, 23 current supply circuit, 23a to 23c FET, 30 controller, 100 injection control device (device 100), 301 temperature range determination unit, 302 injection setting unit, 303 interval determination unit, 304 injection number correction unit

Claims

1. An injection valve that injects fuel into a combustion chamber of an internal combustion engine; a drive circuit including a battery, a boost circuit for boosting power from the battery and charging the power to a capacitor, and a current supply circuit for supplying a drive current to the injector using the power boosted by the boost circuit and charged to the capacitor; A control unit that controls the drive circuit, The control unit is an injection setting unit that sets a target number of injections and a target injection timing per combustion cycle of the internal combustion engine based on an operating condition of the internal combustion engine; an interval determination unit which, when consecutive injections when the number of injections in a single combustion cycle or the total number of injections in two consecutive combustion cycles is at least three are defined as a first injection, a second injection, and a third injection, determines whether or not a first interval from the valve opening timing of the first injection to the valve opening timing of the second injection is equal to or greater than a first threshold value which is a charging time after the capacitor is discharged corresponding to the first injection, and determines whether or not a second interval from the valve opening timing of the second injection to the valve opening timing of the third injection is equal to or greater than a second threshold value which is a charging time after the capacitor is discharged corresponding to the second injection, based on the target number of injections and the target injection timing set by the injection setting unit; and an injection number correction unit that corrects the number of injections per combustion cycle to be less than the target injection number set by the injection setting unit when the interval determination unit determines that the first interval is less than the first threshold value and the second interval is less than the second threshold value.

2. 2. The injection control device according to claim 1, The combustion chamber includes a first combustion chamber and a second combustion chamber, the injector includes a first injector that injects fuel into the first combustion chamber and a second injector that injects fuel into the second combustion chamber, the current supply circuit supplies a drive current to each of the first injector and the second injector; the control unit controls the drive circuit so that the second injector injects fuel into the second combustion chamber after the first injector injects fuel into the first combustion chamber, the first injection is a final injection in a combustion cycle by the first injection valve, the second injection is a first injection in a combustion cycle by the second injection valve, 2. An injection control device according to claim 1, wherein the third injection is a second injection in a combustion cycle by the second injection valve.

3. 3. The injection control device according to claim 1, The control unit further includes a temperature range determination unit that determines whether the temperature of the combustion chamber is equal to or higher than a predetermined temperature, the injection setting unit sets the target injection number and the target injection timing so that fuel is injected a plurality of times from the intake stroke to the compression stroke of the combustion cycle when the temperature range determination unit determines that the temperature of the combustion chamber is lower than the predetermined temperature.

4. 3. The injection control device according to claim 1, The control unit further includes a temperature range determination unit that determines whether the temperature of the combustion chamber is equal to or higher than a predetermined temperature, The injection control device is characterized in that when the temperature range determination unit determines that the temperature of the combustion chamber is equal to or higher than the predetermined temperature, and a predetermined condition is established, the injection setting unit sets the target injection number and the target injection timing so that fuel is injected once during each of the intake stroke and the compression stroke of the combustion cycle.

5. 3. The injection control device according to claim 1, 13. An injection control device according to claim 12, wherein the boost circuit has a single capacitor.

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