Fuel injection controller of internal combustion engine

Abstract

To provide a fuel injection controller of an internal combustion engine capable of suppressing wear of a needle of an injector while minimizing deterioration of a fuel consumption rate and deterioration of exhaust emission.SOLUTION: On the condition that a temperature of an injector is equal to or higher than a predetermined temperature (YES in step ST2) and a pressure of gas fuel acting as a back pressure on a needle is equal to or higher than a predetermined pressure (YES in step ST3), fuel injection timing of the injector is controlled to the retard side. Therefore, it is possible to suppress wear on the needle of the injector while minimizing deterioration of a fuel consumption rate and deterioration of exhaust emissions.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 engines that use liquid fuel such as gasoline, the liquid fuel functions as a lubricant and shock absorber, making it possible to reduce wear caused by the impact load when the needle hits the seat when the valve is closed.

[0006] However, since gas engines cannot use fuel as a lubricant or shock absorber (they run on a dry engine), there is a concern about wear caused by the impact load generated when the needle hits the seat when the valve is closed.

[0007] In particular, when considering the improvement of fuel consumption rate and exhaust emissions, it is preferable to complete fuel injection from the injector (fuel injection during the compression stroke) early to ensure a long time for mixing gas fuel and air in the combustion chamber, but in this case, the movement speed of the needle in the valve closing direction is likely to increase due to the low in-cylinder pressure (the difference between the pressure of the gas fuel acting as the back pressure of the needle and the in-cylinder pressure is large), which creates a situation in which the wear is a concern. In other words, it is possible to retard the fuel injection of the injector in order to reduce the movement speed of the needle in the valve closing direction, but if the fuel injection is always retarded, it will not be possible to improve the fuel consumption rate and exhaust emissions. In this way, suppression of needle wear and improvement of fuel consumption rate and exhaust emissions are in a contradictory relationship.

[0008] 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 suppress wear on the injector needle while minimizing deterioration in fuel consumption rate and exhaust emissions as much as possible. [Means for solving the problem]

[0009] The solution of the present invention for achieving the above object is premised on a fuel injection control device for a fuel injection valve configured to be switchable between an open state in which a needle moves backward to open an injection port and inject gas fuel into a combustion chamber, and a closed state in which the needle moves forward to close the injection port and stop injection of the gas fuel. The fuel injection control device is characterized by including a fuel injection timing control unit that controls the fuel injection timing of the fuel injection valve to the retard side when the gas fuel is injected into the combustion chamber during the compression stroke of an internal combustion engine, under the condition that at least one of the following is satisfied: the temperature of the fuel injection valve estimated or detected is equal to or higher than a predetermined temperature, and the pressure of the gas fuel estimated or detected as a back pressure acting on the needle is equal to or higher than a predetermined pressure.

[0010] When the temperature of the fuel injection valve is equal to or higher than a predetermined temperature, or when the pressure of the gas fuel acting on the needle is equal to or higher than a predetermined pressure, there is a concern that wear may occur due to the impact load acting on the needle when the needle is closed. In this solution, in such a situation, the fuel injection timing of the fuel injection valve is controlled to the retard side, so that the fuel injection valve is closed when the pressure in the combustion chamber (cylinder pressure) is relatively high. In other words, only in a situation where wear is a concern, the fuel injection timing of the fuel injection valve is controlled to the retard side to reduce the moving speed of the needle in the valve closing direction, thereby obtaining the effect of suppressing needle wear. This makes it possible to suppress wear of the injector needle while minimizing deterioration of the fuel consumption rate and exhaust emissions as much as possible. Effect of the Invention

[0011] In the present invention, the fuel injection timing of the fuel injection valve is controlled to the retard side under the condition that at least one of the following conditions is satisfied: the temperature of the fuel injection valve is equal to or higher than a predetermined temperature, and the pressure of the gas fuel acting as the back pressure on the needle is equal to or higher than a predetermined pressure. This makes it possible to suppress wear on the needle of the fuel injection valve while minimizing deterioration of the fuel consumption rate and exhaust emissions as much as possible. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram showing a schematic configuration of a hydrogen engine system. [Diagram 2] FIG. 2 is a cross-sectional view of the injector. [Diagram 3] FIG. 4 is a flowchart showing a procedure of fuel injection retardation control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 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.

[0014] -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.

[0015] 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.

[0016] The engine body 2 includes four cylinders #1 to #4, the first to fourth cylinders #1 to #4, and obtains a rotational driving force by the reciprocating movement of pistons (not shown) that accompany the 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 are arranged 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 that injects hydrogen gas (fuel) supplied from a fuel supply system 5 into the combustion chamber is arranged in each of the cylinders #1 to #4. A water temperature sensor 23 that detects the temperature of engine cooling water, a crank angle sensor 24 that detects the crank angle, and the like are arranged in the cylinder block 21. The configuration of the engine body 2 is not limited to this.

[0017] 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.

[0018] 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 middle of 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 exhaust system 4 is also provided with a urea SCR (Selective Catalytic Reduction) device (not shown). This urea SCR device is a well-known device that purifies NOx in the exhaust by selective reduction using urea water as a reducing agent. The configuration of the exhaust system 4 is not limited to this.

[0019] 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.

[0020] Each injector 54 injects hydrogen gas supplied via a delivery pipe 53 into the combustion chamber at a predetermined timing. The hydrogen gas injected from the 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).

[0021] Here, a specific configuration of the injector 54 will be described. Fig. 2 is a cross-sectional view of the injector 54. As shown in Fig. 2, 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.

[0022] 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.

[0023] 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).

[0024] 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.

[0025] 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 magnitude that allows the needle 54c to remain seated on the valve seat of the seat 54b when normal combustion is occurring in the combustion chamber. In other words, when the electromagnetic coil 54e is de-energized, the needle 54c remains seated on the valve seat of the seat 54b unless abnormal combustion such as pre-ignition occurs in the combustion chamber.

[0026] With this configuration, the pressures that determine the moving speed of the needle 54c when the injector 54 is closed (during the valve closing operation) include the pressure in the valve closing direction, which is the set load, and also the hydrogen gas pressure (approximately equal to the internal pressure of the delivery pipe 53) acting as a back pressure on the needle 54c. Therefore, the higher the hydrogen gas pressure, the higher the moving speed of the needle 54c when the injector 54 is closed. On the other hand, the pressure in the opposite direction to the valve closing direction, that is, the pressure in the direction that hinders the valve closing operation, is the pressure in the combustion chamber. Therefore, the higher the pressure in the combustion chamber, the lower the moving speed of the needle 54c when the injector 54 is closed.

[0027] 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.

[0028] 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 accelerator opening sensor 101 that outputs a detection signal corresponding to the depression amount of an accelerator pedal (not shown). Furthermore, the ECU 100 is connected to the ignition plug 22 (more specifically, an igniter), throttle motor 38, injector 54, etc.

[0029] 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).

[0030] As described above, when considering the improvement of the fuel consumption rate and the exhaust emission, it is preferable to complete the fuel injection from the injector 54 early to secure a long time for mixing the hydrogen gas and the air in the combustion chamber, but in this case, the movement speed of the needle 54c in the valve closing direction is likely to increase due to the low pressure in the cylinder, and there is a concern about wear due to the impact load caused by the needle 54c colliding with the seat 54b. In other words, it is possible to retard the fuel injection of the injector 54 in order to reduce the movement speed of the needle 54c in the valve closing direction, but if the fuel injection is always retarded, it will not be possible to improve the fuel consumption rate and the exhaust emission. In addition, if an attempt is made to improve the exhaust emission, this will lead to an increase in the consumption of urea water in the urea SCR device.

[0031] In consideration of this, the ECU 100 is provided with a fuel injection timing control unit 110 as a functional unit realized by the control program. The fuel injection timing control unit 110 is a functional unit that controls the fuel injection timing of the injector 54. A characteristic function of the fuel injection timing control unit 110 is to control the fuel injection timing of the injector 54 to the retard side under the conditions that the temperature of the injector 54 is equal to or higher than a predetermined temperature and the pressure of hydrogen gas acting as a back pressure on the needle 54c of the injector 54 is equal to or higher than a predetermined pressure. In other words, by opening and closing the injector 54 on the retard side in the compression stroke, the valve closing operation is performed in a situation where the pressure in the combustion chamber is relatively high, thereby slowing down the moving speed of the needle 54c in the valve closing direction.

[0032] -Fuel injection retard control- Next, the fuel injection retard control, which is a characteristic control of this embodiment, will be described. This fuel injection retard control is a control of the fuel injection timing of the injector 54 performed by the fuel injection timing control unit 110, and controls the fuel injection timing of the injector 54 to the retard side on the condition that the temperature of the injector 54 is equal to or higher than a predetermined temperature and the pressure of hydrogen gas acting as a back pressure on the needle 54c of the injector 54 is equal to or higher than a predetermined pressure, as described above. In this embodiment, the control of the fuel injection timing to the retard side is also performed on the condition that abnormal combustion such as pre-ignition is not occurring in the combustion chamber or the situation in which such abnormal combustion occurs is not present.

[0033] 3 is a flowchart showing a procedure for fuel injection retard control, which is repeatedly executed at predetermined time intervals while the engine body 2 is in operation.

[0034] First, in step ST1, various state quantities are acquired. The state quantities acquired here include engine rotation speed, engine torque, hydrogen gas pressure, hydrogen gas temperature, etc. The engine rotation speed is calculated based on a crank angle detection signal from the crank angle sensor 24. The engine torque is calculated based on a detection signal from a torque sensor (not shown) or information on the fuel injection amount and fuel injection timing from each injector 54. The hydrogen gas pressure is acquired from a detection signal from the pressure sensor 57. The hydrogen gas temperature is acquired from a detection signal from the temperature sensor 58.

[0035] In step ST2, the temperature of the injector 54 is estimated, and it is determined whether the estimated temperature of the injector 54 is equal to or higher than a preset threshold value. Methods for estimating the temperature of the injector 54 include estimating the temperature of the injector 54 based on the temperature of the cooling water flowing in the cylinder head, the temperature of the hydrogen gas flowing in the fuel supply system 5, the engine rotation speed, the engine output (engine torque), and the like. The temperature of the injector 54 may also be estimated by applying these state quantities to a map created by a pre-test. Instead of estimating the temperature of the injector 54, a temperature sensor may be directly attached to the injector 54 to detect the temperature of the injector 54.

[0036] If the temperature of the injector 54 is not above the threshold and the result of the NO judgment in step ST2 is NO, it is determined that the hardness of the needle 54c is sufficiently high (i.e., the hardness is not reduced by exposure to high temperatures), and there is no risk of wear due to the impact load described above, and the process returns.

[0037] On the other hand, if the temperature of the injector 54 is equal to or higher than the threshold value and the determination in step ST2 is YES, the process proceeds to step ST3, where it is determined whether or not the pressure of the hydrogen gas is equal to or higher than a preset threshold value. The pressure of the hydrogen gas is detected by the pressure sensor 57. Also, instead of detecting the pressure of the hydrogen gas, the pressure of the hydrogen gas may be estimated. For example, the pressure of the hydrogen gas is estimated based on the internal pressure of the hydrogen storage tank 51, the degree of pressure reduction by the pressure reducing valve 55, the degree of pressure adjustment by the shutoff valve 6, etc.

[0038] If the pressure of the hydrogen gas is not above the threshold value and the result of step ST3 is NO, it is determined that there is no risk of wear due to the impact load described above because the speed of the needle 54c is relatively low, and the process returns.

[0039] On the other hand, if the hydrogen gas pressure is equal to or higher than the threshold value and the determination in step ST3 is YES, the process proceeds to step ST4, where it is determined whether or not the current combustion state of the mixture in the combustion chamber is not in a state that would lead to abnormal combustion such as pre-ignition (the engine operating state is in a pre-ignition non-occurrence region). This determination is made based on parameters related to the temperature in the combustion chamber (engine output, lubricating oil temperature, intake and exhaust temperature, etc.).

[0040] If the pre-ignition is not in the non-occurrence region and the judgment in step ST4 is NO, then, taking into consideration the possibility that pre-ignition may occur if fuel injection retard control is implemented, the process returns to the original state so that fuel injection retard control is not implemented.

[0041] On the other hand, if the pre-ignition is in the non-occurrence region and the determination in step ST4 is YES, the process proceeds to step ST5, where fuel injection retard control is performed. That is, by opening and closing the injector 54 on the retard side in the compression stroke, the valve is closed when the pressure in the combustion chamber is relatively high, and the moving speed of the needle 54c in the valve closing direction is reduced. The retard amount of the fuel injection timing in this case is determined in advance by experiments and simulations as an amount that can suppress the wear caused by the impact load described above according to the temperature of the injector 54 and the pressure of the hydrogen gas. In addition, when the fuel injection retard control is performed in this way, the pressure in the combustion chamber is higher than when the fuel injection retard control is not performed, so that the fuel injection amount per unit time when the injector 54 is in the open state is reduced, and the opening period of the injector 54 is set longer by a predetermined amount.

[0042] The above operations are repeatedly performed at predetermined time intervals while the engine body 2 is in operation.

[0043] -Effects of the embodiment- As described above, in this embodiment, the fuel injection timing of the injector 54 is controlled to the retard side on the condition that the temperature of the injector 54 is equal to or higher than a predetermined temperature and the hydrogen gas pressure acting as a back pressure on the needle 54c of the injector 54 is equal to or higher than a predetermined pressure. This makes it possible to suppress wear on the needle 54c of the injector 54 while minimizing deterioration of the fuel consumption rate and exhaust emissions as much as possible. In addition, because deterioration of exhaust emissions is suppressed, the consumption of urea water in the urea SCR device can be reduced.

[0044] -Other embodiments- The present invention is not limited to the above-described embodiment, and all modifications and applications encompassed 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 fuel injection retard control is performed under the conditions that the temperature of the injector 54 is equal to or higher than a predetermined temperature and the pressure of the hydrogen gas is equal to or higher than a predetermined pressure. However, the present invention is not limited to this, and the fuel injection retard control may be performed when only one of these conditions is satisfied. [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...Fuel injection timing control unit

Claims

[Claim 1] A fuel injection control device for 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 inject 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 fuel injection control device for an internal combustion engine, characterized in that, when the gas fuel is injected toward the combustion chamber during the compression stroke of the internal combustion engine, the fuel injection timing control unit controls the fuel injection timing of the fuel injection valve to the retard side, under the condition that at least one of the following conditions is true: the estimated or detected temperature of the fuel injection valve is equal to or higher than a predetermined temperature, and the estimated or detected pressure of the gas fuel acting on the needle is equal to or higher than a predetermined pressure.

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