Fuel injection control device of internal combustion engine

Abstract

To provide a fuel injection control device of an internal combustion engine capable of appropriately ensuring a fuel injection amount into a combustion chamber even when burnt gas flows into an injector.SOLUTION: A fuel injection control device of an internal combustion engine sets a backflow gas injection period for injecting backflow gas having flowed into an injector into a combustion chamber, and sets the backflow gas injection period to be longer as an amount of backflow gas having flowed into the inside of the injector increases (step ST3). Consequently, an appropriate period for injecting gas fuel into the combustion chamber is ensured, and a shortage of hydrogen gas injected into the combustion chamber is prevented. Therefore, it is possible to prevent deterioration in output from the internal combustion engine and accidental fire.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a fuel injection control device provided in an internal combustion engine, typically a gas engine. [Background technology]

[0002] Conventionally, as disclosed in Patent Document 1, a gas engine that uses gas such as hydrogen as fuel is provided with an injector (direct injection injector) that injects gas fuel supplied from a fuel supply system into the combustion chamber.

[0003] In a typical configuration of this type of injector, a needle biased by a spring in a valve closing direction is housed in a body so as to be able to move back and forth. A seat against which the needle can abut is attached to the tip of the body. An injection port is formed in the seat. An injector configured in this manner can be switched between an open valve state in which the needle moves backward from the seat due to the electromagnetic force of an electromagnetic solenoid, opening the injection port and injecting fuel into the combustion chamber, and a closed valve state in which the electromagnetic force is released, causing the needle to move forward due to the biasing force of the spring and abut against the seat, closing the injection port and stopping fuel injection. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2021-105350 A Summary of the Invention [Problem to be solved by the invention]

[0005] In this type of engine, if abnormal combustion such as pre-ignition occurs in the combustion chamber, the pressure in the combustion chamber may rise more than expected, causing burnt gases to flow into the injector (causing a backflow of burnt gas).

[0006] In this case, when the injector injects fuel in the next cycle, burnt gas is injected first, and then the original fuel (gas fuel) is injected into the combustion chamber. Since the fuel injection period of the injector has been set assuming that gas fuel is injected from the initial valve opening time, if burnt gas has flowed into the injector, the amount of gas fuel injected into the combustion chamber will be insufficient, which may result in a decrease in engine output or a misfire.

[0007] The present invention has been made in consideration of the above points, and its object is to provide a fuel injection control device for an internal combustion engine that can properly ensure the amount of fuel injected into the combustion chamber even if burnt gas flows into the inside of the injector. [Means for solving the problem]

[0008] The solution of the present invention for achieving the above object is based on a fuel injection control device for an internal combustion engine having a fuel injection valve configured to be switchable between an open state in which a needle moves backward to open an injection port to enable injection of gas fuel into a combustion chamber, and a closed state in which the needle moves forward to close the injection port to stop injection of the gas fuel. The fuel injection control device includes a backflow gas amount calculation unit that calculates an amount of backflow gas that has flowed from the combustion chamber into the fuel injection valve, and a backflow gas injection period setting unit that sets a backflow gas injection period for injecting the backflow gas that has flowed into the fuel injection valve into the combustion chamber as a period different from a period for injecting the gas fuel into the combustion chamber, and the backflow gas injection period setting unit sets the backflow gas injection period to be longer as the amount of the backflow gas that has flowed into the fuel injection valve increases.

[0009] When backflow gas flows into the fuel injection valve from the combustion chamber, the backflow gas injection period is set as a period different from the period during which the gas fuel, which is the original fuel, is injected from the fuel injection valve into the combustion chamber. The backflow gas injection period is set longer as the amount of backflow gas flowing into the fuel injection valve increases, so that most of the backflow gas is injected from the fuel injection valve into the combustion chamber during the backflow gas injection period (so-called waste injection). This ensures an appropriate period during which the gas fuel, which is the original fuel, is injected into the combustion chamber, and prevents the amount of gas fuel injected into the combustion chamber from becoming insufficient. This prevents a decrease in the output of the internal combustion engine and misfires. The backflow gas injection period may be set as a period during which the gas fuel, which is the original fuel, is injected from the fuel injection valve continuously, or may be set as another period (for example, during the exhaust stroke or the intake stroke). Effect of the Invention

[0010] In the present invention, a backflow gas injection period for injecting the backflow gas that has flowed into the fuel injection valve into the combustion chamber is set, and the greater the amount of backflow gas that has flowed into the fuel injection valve, the longer the backflow gas injection period is set. This ensures an appropriate period for injecting gas fuel into the combustion chamber, and prevents the amount of gas fuel injected into the combustion chamber from becoming insufficient. This makes it possible to prevent a decrease in the output of the internal combustion engine and misfires. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing a schematic configuration of a hydrogen engine system. [Diagram 2] FIG. 2(a) is a cross-sectional view of the entire injector, FIG. 2(b) is an enlarged view of the area surrounded by the dashed line in FIG. 2(a), and FIG. 2(c) is a schematic diagram showing the state in which burnt gas has flowed into the inside of the injector. [Diagram 3] FIG. 11 is a flowchart showing a procedure for backflow gas injection control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, the present invention will be described as being applied to a system equipped with a four-cylinder hydrogen engine (an internal combustion engine fueled by hydrogen gas) mounted on a vehicle.

[0013] -Overview of hydrogen engine system- First, before describing the configuration of the injector and the control of the injector, a brief description will be given of the schematic configuration of the hydrogen engine system according to this embodiment.

[0014] Fig. 1 is a diagram showing a schematic configuration of a hydrogen engine system 1 according to this embodiment. As shown in Fig. 1, the hydrogen engine system 1 according to this embodiment includes an intake system 3, an exhaust system 4, and a fuel supply system 5, which are connected to an engine body (internal combustion engine) 2. Each of these will be briefly described below.

[0015] The engine body 2 includes four cylinders #1 to #4, and generates a rotational driving force by reciprocating movement of pistons (not shown) associated with combustion of a mixture (a mixture of hydrogen gas and air) in the combustion chambers (inside the cylinders) of these cylinders #1 to #4. A cylinder head (not shown) is attached to the upper end of a cylinder block 21 in the engine body 2, and spark plugs 22 (not shown) are disposed in the cylinder head so as to face the combustion chambers of each of the cylinders #1 to #4. Also, an injector (direct injection injector: fuel injection valve) 54 is disposed in each of the cylinders #1 to #4, which injects hydrogen gas (gas fuel) supplied from a fuel supply system 5 into the combustion chamber. A water temperature sensor 23 for detecting the temperature of engine cooling water, a crank angle sensor 24 for detecting the crank angle, and the like are disposed in the cylinder block 21. The configuration of the engine body 2 is not limited to this.

[0016] The intake system 3 includes an intake passage 31, a surge tank 32, and an intake manifold 33 for supplying intake air (air) toward the combustion chambers of each of the cylinders #1 to #4. An air cleaner 34, an air flow meter 35, an intake air temperature sensor 36 (built into the air flow meter 35), and an electronically controlled throttle valve 37 are arranged on the upstream side of the intake passage 31 (upstream side of the flow of intake air). The throttle valve 37 is driven by a throttle motor 38. An intake valve (not shown) is arranged at the downstream end of an intake port formed in the cylinder head, and intake air is supplied into the combustion chamber by opening this intake valve. The configuration of the intake system 3 is not limited to this. For example, the configuration may be such that the surge tank 32 is not included.

[0017] The exhaust system 4 includes an exhaust manifold 41 and an exhaust passage 42. A catalytic converter 43 for purifying exhaust (mainly NOx in the exhaust) is disposed in the exhaust passage 42. An exhaust valve (not shown) is disposed at the upstream end of an exhaust port formed in the cylinder head, and exhaust gas is discharged from the combustion chamber when this exhaust valve is opened. The configuration of the exhaust system 4 is not limited to this.

[0018] The fuel supply system 5 includes a hydrogen storage tank (high pressure tank) 51, a fuel supply pipe 52, a delivery pipe 53, and an injector 54 for each cylinder. The hydrogen storage tank 51 is a tank that stores hydrogen under high pressure. The fuel supply pipe 52 is provided with a pressure reducing valve 55 for reducing the pressure of the hydrogen gas supplied to the delivery pipe 53, a relief valve 56 that opens when the fuel pressure inside the fuel supply pipe 52 exceeds a predetermined value, and a shutoff valve 6 for adjusting the pressure of the fuel supplied to the delivery pipe 53. The delivery pipe 53 is provided with a pressure sensor 57 for detecting the pressure of the hydrogen gas in the delivery pipe 53, and a temperature sensor 58 for detecting the temperature of the hydrogen gas in the delivery pipe 53.

[0019] Each injector 54 injects hydrogen gas supplied via a delivery pipe 53 into the combustion chamber at a predetermined timing (for example, a predetermined timing during the compression stroke). The hydrogen gas injected from this injector 54 into the combustion chamber mixes with air supplied from the intake system 3 to form an air-fuel mixture in the combustion chamber. This mixture is ignited by the spark plug 22 and combusted. The high-temperature, high-pressure combustion gas generated thereby pushes the pistons down from top dead center during the expansion stroke of each of the cylinders #1 to #4, rotating the crankshaft and generating a rotational driving force (output torque).

[0020] Here, a specific configuration of the injector 54 will be described. Fig. 2(a) is a cross-sectional view of the entire injector 54. As shown in Fig. 2(a), the injector 54 has a body 54a, a seat 54b, a needle 54c, a spring 54d, and an electromagnetic coil 54e. The body 54a is cylindrical. A seat 54b is held at a tip portion 54g of the body 54a. An injection port 54f for injecting hydrogen gas into the combustion chamber is formed in the seat 54b.

[0021] The needle 54c is housed in the body 54a in a state in which it can move toward the seat 54b (forward direction) and away from the seat 54b (rearward direction). When the needle 54c is seated on the valve seat of the seat 54b, the injection port 54f is closed. On the other hand, when the needle 54c is away from the valve seat of the seat 54b as shown in FIG. 2(b), which is an enlarged view of the area surrounded by the dashed line in FIG. 2(a), the injection port 54f is opened.

[0022] An internal fuel passage 54h through which hydrogen gas flows is formed between the inner circumferential surface of the body 54a and the needle 54c. The internal fuel passage 54h is connected to the delivery pipe 53. Therefore, when the injector 54 is opened, the internal fuel passage 54h is connected to the injection port 54f. At this time, if the pressure in the internal fuel passage 54h is higher than the pressure in the combustion chamber, fuel is injected from the injection port 54f into the combustion chamber as shown by the solid arrow in FIG. 2(b).

[0023] The spring 54d biases the needle 54c in a direction to press the needle 54c against the seat 54b. That is, when the injector 54 is closed, the greater the biasing force of the spring 54d, the greater the force pressing the needle 54c against the seat 54b. When the electromagnetic coil 54e is energized, an electromagnetic force is generated in a direction to move the needle 54c away from the seat 54b. Then, the needle 54c moves away from the seat 54b against the force of the spring 54d pressing the needle 54c against the seat 54b. This opens the injector 54. On the other hand, when the energization of the electromagnetic coil 54e is stopped, the needle 54c is pressed against the seat 54b by the biasing force of the spring 54d. This closes the injector 54.

[0024] The force with which the spring 54d presses the needle 54c against the seat 54b when the injector 54 is closed is called the "set load". At this time, the set load is set to a value large enough to maintain the needle 54c seated on the valve seat of the seat 54b when normal combustion is occurring in the combustion chamber. That is, when the electromagnetic coil 54e is de-energized, the needle 54c will maintain its seated state on the valve seat of the seat 54b unless abnormal combustion such as pre-ignition occurs in the combustion chamber. In other words, if abnormal combustion occurs in the combustion chamber and the pressure in the combustion chamber becomes excessively high, the needle 54c may move in a direction away from the seat 54b against the fuel pressure supplied to the injector 54 and the set load. In this case, the needle 54c will move away from the seat 54b and the injection port 54f will not be closed.

[0025] The ECU (Electronic Control Unit) 100 is a known device that includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and a backup RAM. The CPU executes various arithmetic processing based on various control programs and maps stored in the ROM. The RAM temporarily stores the results of calculations performed by the CPU and data input from each sensor, and the backup RAM stores data that should be saved when the engine is stopped, for example.

[0026] The ECU 100 is connected to the above-mentioned water temperature sensor 23, crank angle sensor 24, air flow meter 35, intake air temperature sensor 36, pressure sensor 57, temperature sensor 58, etc. Also connected to the ECU 100 is an in-cylinder pressure sensor 101 that detects the pressure in the combustion chamber. This in-cylinder pressure sensor 101 is provided for each cylinder. Furthermore, the ECU 100 is connected to the ignition plug 22 (more specifically, an igniter), throttle motor 38, injector 54, etc.

[0027] Based on signals from the various sensors, the ECU 100 executes various controls including drive control of the injector 54 (control of the amount of fuel injection), control of the ignition timing of the spark plug 22, and drive control of the throttle motor 38 (control of the amount of intake air).

[0028] As described above, when abnormal combustion such as pre-ignition occurs in the combustion chamber, the pressure in the combustion chamber increases more than expected, which may cause a situation in which burnt gas (combustion gas) flows into the injector 54 (a backflow of burnt gas occurs) (see the dashed arrow in FIG. 2(b)). Pre-ignition is likely to occur during the compression stroke. In a hydrogen engine, hydrogen gas is generally injected from the injector 54 into the combustion chamber during the compression stroke. Therefore, when pre-ignition occurs while the injector 54 is open, the pressure in the combustion chamber may become higher than the supply fuel pressure, which may cause a situation in which burnt gas flows into the injector 54. Even if the power supply to the injector 54 has already been terminated when pre-ignition occurs, if the pressure in the combustion chamber is higher than the sum of the supply fuel pressure and the set load, the pressure in the combustion chamber may move the needle 54c to the valve opening side, which may cause a situation in which burnt gas flows into the injector 54. FIG. 2(c) is a schematic diagram showing a state in which burnt gas has flowed into the injector 54. In FIG. 2(c), the dotted portion of the internal fuel passage 54h of the injector 54 is the burnt gas. Hereinafter, the burnt gas that has flowed into the injector 54 may be referred to as backflow gas. When such a situation occurs, in the fuel injection from the injector 54 in the next cycle, the burnt gas is injected first, and then the original fuel (hydrogen gas) is injected into the combustion chamber. The fuel injection period of a conventional general injector is set on the assumption that hydrogen gas is injected from the initial opening of the valve. Therefore, when burnt gas flows into the injector, the amount of hydrogen gas injected into the combustion chamber is insufficient, which may cause a decrease in engine output or a misfire.

[0029] In consideration of this point, the ECU 100 is provided with a backflow gas amount calculation unit 110 and a backflow gas injection period setting unit 120 as functional units realized by the control program. The backflow gas amount calculation unit 110 is a functional unit that calculates the amount of burnt gas (backflow gas) that has flowed from the combustion chamber into the inside of the injector 54 (internal fuel passage 54h). The backflow gas injection period setting unit 120 is a functional unit that sets a backflow gas injection period for injecting the backflow gas that has flowed into the inside of the injector 54 into the combustion chamber as a period different from the period for injecting hydrogen gas (gas fuel) toward the combustion chamber. In this embodiment, the backflow gas injection period is set as a period that continues with the period for injecting hydrogen gas, which is the original fuel, from the injector 54. In other words, the backflow gas injection period is set as a period preceding the period for injecting hydrogen gas, and the injector 54 is set to be in an open state continuously during the backflow gas injection period and the injection period of hydrogen gas. Hereinafter, the functions of the backflow gas amount calculation unit 110 and the backflow gas injection period setting unit 120 will be specifically described.

[0030] The backflow gas amount calculation unit 110 calculates the amount of backflow gas from each piece of information on the pressure inside the combustion chamber, the supply fuel pressure, the engine speed, and the end timing of fuel injection by the injector 54. The pressure inside the combustion chamber is detected by the in-cylinder pressure sensor 101. The supply fuel pressure is detected by the pressure sensor 57. The engine speed is calculated based on a crank angle detection signal from the crank angle sensor 24. The end timing of fuel injection is detected based on a control signal for the injector 54.

[0031] When the injector 54 is not closed due to abnormal combustion such as pre-ignition, the higher the pressure in the combustion chamber (for example, the maximum pressure during the cycle), the greater the pressure difference between the combustion chamber and the injector 54, and therefore the greater the amount of backflow gas flowing from the combustion chamber into the injector 54. Also, the lower the fuel pressure supplied to the injector 54, the greater the pressure difference between the combustion chamber and the injector 54, and therefore the greater the amount of backflow gas flowing from the combustion chamber into the injector 54. Also, the lower the engine rotation speed, the longer the duration of the state in which the injector 54 is not closed due to the excessively high pressure in the combustion chamber, and therefore the greater the amount of backflow gas flowing from the combustion chamber into the injector 54. Also, the later the end timing of fuel injection by the injector 54, the longer the period during which the backflow gas flows from the combustion chamber into the injector 54, and therefore the greater the amount of backflow gas flowing from the combustion chamber into the injector 54.

[0032] Therefore, the backflow gas amount calculation unit 110 calculates the amount of backflow gas so that the amount of backflow gas flowing from the combustion chamber into the injector 54 increases as the maximum in-cylinder pressure during one combustion stroke increases, the fuel pressure supplied to the injector 54 decreases, the engine rotation speed decreases, and the fuel injection by the injector 54 ends later. For example, the backflow gas amount Qr is calculated using the following formula (1). "F1", "F2", "F3", and "F4" in this formula (1) are coefficients set based on the shape of the combustion chamber, the characteristics of the injector 54, and the like. For example, the coefficients are set so that the amount of backflow gas decreases as the design value of the set load of the injector 54 increases.

[0033] Backflow gas volume Qr = F1 x PCY-F2 x PD-F3 x NEA-F4 x TIE … (1) Here, PCY is the cylinder pressure, PD is the supplied fuel pressure, NEA is the engine speed, and TIE is the end timing of fuel injection (a value that becomes smaller as the angle is retarded).

[0034] The backflow gas injection period setting unit 120 uses the backflow gas amount Qr calculated by the backflow gas amount calculation unit 110 to calculate the backflow gas injection period according to the following formula (2).

[0035] Backflow gas injection period Tr = Qr / injector injection rate @ hydrogen gas pressure at the time of calculation...(2) Here, "injector injection rate @ hydrogen gas pressure at time of calculation" is the injection rate of the injector 54 according to the hydrogen gas pressure (supply fuel pressure) at the time of calculating the backflow gas injection period Tr. In other words, the higher the hydrogen gas pressure, the larger the injection rate of the injector. The backflow gas injection period Tr calculated by this formula (2) becomes a larger value (longer period) as the amount of backflow gas that flows into the injector 54 (backflow gas amount Qr) increases.

[0036] The valve opening start timing of the injector 54 is set earlier (to the advance side) by the backflow gas injection period Tr calculated in this way. For example, the valve opening start timing of the injector 54 is set earlier by the backflow gas injection period Tr on the advance side with respect to a reference valve opening start timing (a valve opening start timing set to obtain the amount of hydrogen gas supply calculated to obtain the required output, and a valve opening start timing of the injector 54 when it is assumed that no backflow gas flows into the injector 54) that is set based on the accelerator opening detected by an accelerator opening sensor (not shown). As a result, during this backflow gas injection period Tr, substantially the entire amount of backflow gas is injected, and from the subsequent reference valve opening start timing, the original fuel (hydrogen gas) is injected toward the combustion chamber.

[0037] -Backflow gas injection control- Next, a description will be given of the backflow gas injection control, which is a characteristic control of this embodiment. Fig. 3 is a flowchart showing the procedure of the backflow gas injection control. This flowchart is repeatedly executed at predetermined time intervals while the engine body 2 is in operation.

[0038] First, in step ST1, it is determined whether or not pre-ignition has occurred. This determination is made based on the pressure inside the combustion chamber detected by the in-cylinder pressure sensor 101. Alternatively, a knock sensor (not shown) may be provided to determine whether or not pre-ignition has occurred depending on whether or not knocking has occurred in the engine body 2.

[0039] If pre-ignition has not occurred and the determination in step ST1 is NO, it is determined that there is no situation in which backflow gas would flow into the injector 54, and the process returns. On the other hand, if pre-ignition has occurred and the determination in step ST1 is YES, the process proceeds to step ST2, where the amount of backflow gas that has flowed into the injector 54 is calculated. This calculation is performed using the above-mentioned formula (1).

[0040] In step ST3, the backflow gas injection period Tr is calculated using the calculated amount of backflow gas, using the above-mentioned formula (2).

[0041] In step ST4, it is determined whether the backflow gas injection start time in the next cycle for the cylinder for which the backflow gas injection period Tr has been calculated has been reached. As described above, the backflow gas injection start time is set as the time advanced by the backflow gas injection period Tr from the valve opening start time of the injector 54 when it is assumed that no backflow gas is flowing into the injector 54 (the reference valve opening start time). If the backflow gas injection start time has been reached and the determination is YES in step ST4, the process proceeds to step ST5, where the injector 54 is opened to start injecting the backflow gas.

[0042] In step ST6, it is determined whether or not the fuel injection end time has been reached. This fuel injection end time is set as the time when the injection period of hydrogen gas ends after the aforementioned backflow gas injection period Tr. Until the fuel injection end time is reached, the determination in step ST6 is NO, and the injector 54 is maintained in an open state. If the determination in step ST6 is YES because the fuel injection end time has been reached, the process proceeds to step ST7, and the injector 54 is closed. The above operations are repeatedly performed at predetermined time intervals while the engine body 2 is operating.

[0043] -Effects of the embodiment- As described above, in this embodiment, a backflow gas injection period Tr is set for injecting the backflow gas that has flowed into the injector 54 into the combustion chamber, and the backflow gas injection period Tr is set longer as the amount of backflow gas that has flowed into the injector 54 increases. This ensures an appropriate period for injecting hydrogen gas into the combustion chamber, and prevents the amount of hydrogen gas injected into the combustion chamber from becoming insufficient. This makes it possible to prevent a decrease in engine output and misfires.

[0044] -Other embodiments- The present invention is not limited to the above-described embodiment, and all modifications and applications within the scope of the claims and equivalents thereto are possible.

[0045] For example, in the above embodiment, the present invention has been described as being applied to a system equipped with a four-cylinder hydrogen engine mounted on a vehicle. The present invention is not limited to this, and can also be applied to gas engines used for purposes other than vehicles. The number of cylinders is not limited to four. The fuel is not limited to hydrogen gas.

[0046] In the above embodiment, the backflow gas injection period Tr is a period during which the injector 54 continues to inject gas fuel, which is the original fuel. In other words, the backflow gas injection period Tr is set as a period preceding the period during which hydrogen gas is injected. The present invention is not limited to this, and the backflow gas injection period Tr may be set as another period. For example, this may be during the exhaust stroke or the intake stroke. In other words, it is sufficient that the backflow gas injection period Tr is set as a period during which the backflow gas in the injector 54 is discharged at the start of the period during which hydrogen gas is injected. [Industrial Applicability]

[0047] The present invention is applicable as a fuel injection control device that controls fuel injection from an injector provided in a hydrogen engine. [Explanation of symbols]

[0048] 54... Injector (fuel injection valve) 54c... Needle 54f... Injection port 100... ECU 110... backflow gas amount calculation unit 120... backflow gas injection period setting unit

Claims

[Claim 1] A fuel injection control device for an internal combustion engine equipped with a fuel injection valve configured to be switchable between an open valve state in which a needle moves backward to open an injection port and enable injection of gas fuel into a combustion chamber, and a closed valve state in which the needle moves forward to close the injection port and stop injection of the gas fuel, a backflow gas amount calculation unit that calculates an amount of backflow gas that has flowed from the combustion chamber into the fuel injection valve; a backflow gas injection period setting unit that sets a backflow gas injection period for injecting the backflow gas that has flowed into the fuel injection valve into the combustion chamber as a period different from a period for injecting the gas fuel toward the combustion chamber, 2. A fuel injection control device for an internal combustion engine, wherein the backflow gas injection period setting unit sets the backflow gas injection period to a longer period as an amount of the backflow gas flowing into the fuel injection valve increases.

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