Fuel injection control device for internal combustion engine

Abstract

To improve fuel injection accuracy.SOLUTION: A fuel supply device 200 for an internal combustion engine 10 includes: a fuel tank 20 that stores gaseous fuel; a fuel injection valve 15 for supplying fuel to a cylinder; a fuel supply passage for supplying fuel in the fuel tank 20 to the fuel injection valve 15; and a shut-off valve 40 for shutting off the fuel supply passage. When engine load of the internal combustion engine 10 is less than prescribed load, a control device 100 executes valve closing processing for closing the shut-off valve 40.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] For example, in the internal combustion engine described in Patent Document 1, the drive of the fuel pump is controlled so that the fuel pressure, which is the pressure of the fuel supplied to the fuel injection valve, is lower when the engine load is low compared to when the engine load is high. Lowering the fuel pressure in this way lengthens the fuel injection time required to ensure the fuel injection amount calculated according to the engine load. A longer fuel injection time reduces the variation in the injection amount compared to when the fuel injection time is short. Therefore, fuel injection accuracy is improved even when the engine load is low and the fuel injection amount is small. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-77730 Summary of the Invention [Problem to be solved by the invention]

[0004] In internal combustion engines that use gaseous fuel, the fuel is stored in a tank under high pressure. Therefore, a fuel pump for increasing the fuel pressure is often not provided in the fuel supply system. Therefore, in internal combustion engines that use gaseous fuel, it is desirable to improve injection accuracy at low engine loads by reducing the fuel pressure in a manner other than by controlling the drive of the fuel pump. [Means for solving the problem]

[0005] A fuel injection control device for an internal combustion engine that solves the above problem is a fuel injection control device that is applied to an internal combustion engine equipped with a fuel supply device having a tank that stores gaseous fuel, a fuel injection valve that supplies fuel to a cylinder, a fuel supply passage that supplies fuel in the tank to the fuel injection valve, and a valve provided in the fuel supply passage. This fuel injection control device executes a valve closing process to close the valve when the engine load of the internal combustion engine is less than a predetermined load.

[0006] According to this configuration, when the engine load of the internal combustion engine is below a predetermined load and the amount of fuel injected from the fuel injection valve is small, the valve that adjusts the amount of fuel flowing through the fuel supply passage is closed. If fuel injection continues with this valve closed, the fuel flow from the fuel passage between the valve and the fuel injection valve gradually decreases, and the pressure of the fuel supplied to the fuel injection valve also gradually decreases. When the pressure of the fuel supplied to the fuel injection valve decreases, the fuel injection time required to ensure the fuel injection amount calculated according to the engine load becomes longer. When the fuel injection time is longer, the injection amount variation is smaller than when the fuel injection time is shorter. Therefore, fuel injection accuracy is improved even when the engine load is low in an internal combustion engine that uses gaseous fuel. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic diagram showing a fuel supply system and a control device for an internal combustion engine according to an embodiment; [Figure 2] 4 is a flowchart showing a procedure of a process executed by the control device of the embodiment. [Figure 3] 3A and 3B are time charts illustrating the operation of the embodiment, in which Fig. 3A shows the change in fuel pressure and Fig. 3B shows the state of the shutoff valve. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, a fuel injection control device for an internal combustion engine according to one embodiment will be described. <Fuel supply system and control device for internal combustion engines> The internal combustion engine 10 shown in FIG. 1 is an internal combustion engine that uses hydrogen gas as a gaseous fuel.

[0009] The fuel supply device 200 provided in the internal combustion engine 10 includes a fuel injection valve 15, a fuel tank 20, a fuel pipe 30, a shutoff valve 40, a pressure reducing valve 50, and a delivery pipe 60. The fuel injection valve 15 supplies fuel to the cylinders of the internal combustion engine 10 .

[0010] The fuel tank 20 stores hydrogen gas, which is a gaseous fuel, in a compressed state. A first end of the fuel pipe 30 is connected to the fuel tank 20. A second end of the fuel pipe 30 is connected to the delivery pipe 60.

[0011] The fuel injection valve 15 is connected to the delivery pipe 60. The fuel piping 30 and the delivery pipe 60 form a fuel supply passage that supplies fuel from the fuel tank 20 to the fuel injection valve 15.

[0012] The hydrogen gas stored in the fuel tank 20 is supplied to the fuel injection valve 15 via the fuel pipe 30 and the delivery pipe 60 . The shutoff valve 40 is an electromagnetic valve and is disposed at a first end of the fuel pipe 30. The shutoff valve 40 opens and closes the flow path of the fuel pipe 30.

[0013] The pressure reducing valve 50 is an electromagnetic valve and is provided in the fuel piping 30 at a position between the shutoff valve 40 and the delivery pipe 60. The pressure reducing valve 50 adjusts the fuel pressure, which is the pressure of the hydrogen gas supplied to the fuel injection valve 15, to a pressure that corresponds to the engine operating state.

[0014] The control device 100 performs various controls such as fuel injection for the internal combustion engine 10 by controlling various control objects such as the fuel injection valve 15, the shutoff valve 40, and the pressure reducing valve 50. The control device 100 includes a CPU 110 and a memory 120 configured from a ROM, a RAM, etc., and performs various controls by the CPU 110 executing programs stored in the memory 120.

[0015] The control device 100 references various values ​​necessary for controlling the internal combustion engine 10. For example, the control device 100 references the pressure detected by a pressure sensor 70 provided in the delivery pipe 60. The pressure detected by this pressure sensor 70 is the pressure of the fuel supplied to the fuel injection valve 15. Hereinafter, this fuel pressure will be referred to as the fuel pressure PF. The control device 100 also references a detection signal from an accelerator position sensor 71 that detects an accelerator operation amount ACCP, which is the amount of operation of the accelerator pedal operated by the driver of the vehicle equipped with the internal combustion engine 10. The control device 100 also references a detection signal from a speed sensor 72 that detects the vehicle speed SP of the vehicle equipped with the internal combustion engine 10. In addition, the control device 100 references detection signals for calculating the engine rotation speed NE and a detection signal for the intake air amount GA. The control device 100 also calculates an engine load factor KL. The engine load factor KL is a parameter that determines the amount of air charged into a cylinder and is the ratio of the amount of inflow air per combustion cycle of one cylinder to a reference inflow air amount. The reference inflow air amount may be an amount that is variably set depending on the engine rotation speed NE.

[0016] <Processing performed by the control device> The control device 100 keeps the shutoff valve 40 open while the engine is operating, thereby permitting fuel supply from the fuel tank 20 to the fuel pipe 30. On the other hand, when the engine operation stops, the control device 100 closes the shutoff valve 40, thereby stopping the fuel supply from the fuel tank 20 to the fuel pipe 30.

[0017] The control device 100 calculates a target pressure PFt, which is a target value of the fuel pressure PF, based on the engine load factor KL and the like. Then, the control device 100 controls the pressure reducing valve 50 so as to obtain the target pressure PFt. Here, a lower limit value of the target pressure PFt when the engine load is equal to or greater than a predetermined load is predetermined as a second pressure PF2. Note that the control device 100 determines that the engine load is equal to or greater than the predetermined load when a negative determination is made in the processing of S100 (described later) or when a negative determination is made in the processing of S110 (described later).

[0018] The control device 100 calculates a target output Pe, which is a target value of the output required of the internal combustion engine 10, based on the accelerator operation amount ACCP and the vehicle speed SP. When the target output Pe is large, the control device 100 executes control to reduce the air-fuel ratio of the mixture compared to when the target output Pe is small. More specifically, the control device 100 basically maintains the throttle valve provided in the intake passage of the internal combustion engine 10 at an opening equal to or greater than a predetermined value, for example, an opening near full open. The control device 100 sets the required injection amount Qd so that the required injection amount Qd increases as the target output Pe increases. The required injection amount Qd is a target value for the fuel injected from the fuel injection valve 15. The control device 100 calculates the fuel injection time of the fuel injection valve 15 based on the required injection amount Qd and the fuel pressure PF. When the required injection amount Qd is large, the control device 100 sets a longer fuel injection time than when it is small. Furthermore, when the fuel pressure PF is low, the control device 100 sets a longer fuel injection time than when it is high. Then, the control device 100 opens the fuel injection valve 15 for the set fuel injection time, thereby causing the fuel injection valve 15 to inject fuel in an amount corresponding to the required injection amount Qd.

[0019] In this way, in the internal combustion engine 10, the engine output is basically adjusted by changing the air-fuel ratio of the mixture through adjustment of the fuel injection amount, not the intake air amount. <Shut-off valve opening and closing process> The control device 100 executes a process for opening and closing the shutoff valve 40 when the engine load is less than a predetermined load.

[0020] Fig. 2 shows a processing procedure including such valve-opening processing and valve-closing processing. The processing shown in Fig. 2 is performed by CPU 110 executing a program stored in memory 120 of control device 100 at predetermined intervals while the engine is running. Note that, hereinafter, step numbers are represented by numbers preceded by "S."

[0021] When this process starts, the control device 100 acquires the vehicle speed SP and determines whether the acquired vehicle speed SP is less than a predetermined threshold value SPref (S100). The threshold value SPref is an adaptive value for determining whether the current engine load is less than a predetermined load. Here, the predetermined load refers to the following load: When the engine load is low and the required injection amount Qd is small, the fuel injection time is shortened, which may increase the variation in the fuel injection amount. Therefore, in order to suppress such variation, it is desirable to lengthen the fuel injection time by setting the fuel pressure PF to a pressure less than the second pressure. Therefore, in this embodiment, a low load state in which the variation in the fuel injection amount may increase is assumed as the predetermined load. The vehicle speed SP is a value related to such a low load state. Therefore, when the vehicle speed SP is less than the predetermined threshold value SPref, the control device 100 determines that one condition for determining that such a low load state exists is satisfied.

[0022] When it is determined in the process of S100 that the vehicle speed SP is less than the threshold value SPref (S100: YES), the control device 100 acquires the accelerator operation amount ACCP and determines whether the acquired accelerator operation amount ACCP is less than a predetermined threshold value ACCPref (S110). The threshold value ACCPref is also an adaptive value for determining whether the current engine load is less than the above-mentioned predetermined load. The accelerator operation amount ACCP is a value related to the above-mentioned low-load state. Therefore, when the accelerator operation amount ACCP is less than the predetermined threshold value ACCPref, the control device 100 determines that another condition for determining that such a low-load state exists is satisfied. Note that when the determinations in both the process of S100 and the process of S110 are YES, it is determined that the current engine load is in the above-mentioned low-load state.

[0023] When it is determined in the process of S110 that the accelerator operation amount ACCP is less than the threshold ACCPref (S100: YES), the control device 100 acquires the current fuel pressure PF and determines whether the acquired fuel pressure PF is less than the first pressure PF1 (S120). The first pressure PF1 is a predetermined pressure that is lower than the second pressure PF2. More specifically, the first pressure PF1 is set to a value slightly higher than the lower limit value of the fuel pressure PF at which the amount of fuel required for combustion of the air-fuel mixture can be injected under low load conditions, such as idling.

[0024] When it is determined that the fuel pressure PF is not less than the first pressure PF1 (S120: NO), the control device 100 executes a valve closing process to close the shutoff valve 40 (S130). On the other hand, when the control device 100 determines that the fuel pressure PF is less than the first pressure PF1 (S120: YES), it executes a valve opening process to open the shutoff valve 40 (S140). As this valve opening process, the control device 100 executes a process to open the shutoff valve 40 for a predetermined time T1. The time T1 is a predetermined time for which the shutoff valve 40 is open, which is necessary to increase the fuel pressure PF to a pressure close to the second pressure PF2. When the time T1 has elapsed since the shutoff valve 40 was opened, the control device 100 closes the shutoff valve 40 again.

[0025] Then, when the process of S130 or the process of S140 is completed, or when a negative determination is made in the process of S100, or when a negative determination is made in the process of S110, the control device 100 ends this process in the current cycle.

[0026] <effect> The operation of this embodiment will be described. Fig. 3 shows a time chart illustrating the operation of this embodiment. Fig. 3(A) shows the change in fuel pressure, and Fig. 3(B) shows the state of the shutoff valve. After time t1 in the time chart shown in Fig. 3, the engine load is low enough that both the processing of S100 and the processing of S110 shown in Fig. 2 are judged to be positive.

[0027] 2 is determined to be negative, the shutoff valve 40 is closed. If fuel injection continues with the shutoff valve 40 closed, the fuel flow path from the shutoff valve 40 to the fuel injection valve 15 gradually decreases, and the fuel pressure PF also gradually decreases.

[0028] At time t2, when the fuel pressure PF becomes less than the first pressure PF1, the shutoff valve 40 is opened. When the shutoff valve 40 opens, fuel is supplied to the fuel flow path between the shutoff valve 40 and the fuel injection valve 15, so the fuel pressure PF increases and recovers. Then, at time t3, when the time T1 has elapsed since time t2, the shutoff valve 40 is closed again.

[0029] After time t3, the above-described closing and opening processes of the shutoff valve 40 are repeatedly executed, so that the fuel pressure PF is adjusted to a pressure within the range of not less than the first pressure PF1 and less than the second pressure PF2.

[0030] <Effects> The effects of this embodiment will be described. (1) When the engine load of the internal combustion engine 10 is less than a predetermined load and the amount of fuel injected from the fuel injection valve 15 is small, the shutoff valve 40 is closed, thereby reducing the fuel pressure PF. When the fuel pressure PF is reduced, the fuel injection time required to ensure the required injection amount Qd calculated according to the engine load becomes longer. When the fuel injection time is longer, the variation in the fuel injection amount becomes smaller compared to when the fuel injection time is short. Therefore, even when the engine load is low in an internal combustion engine that uses gaseous fuel, the fuel injection accuracy is improved.

[0031] (2) Because there is little variation in the fuel injection amount when the engine load is low, fluctuations in engine torque during idling are reduced, thereby suppressing vibrations and noise caused by fluctuations in engine torque.

[0032] (3) If the engine load of the internal combustion engine 10 remains below a predetermined load for a long period of time, causing the execution of the valve closing process to be prolonged, the fuel pressure PF may drop excessively, making it impossible to inject the fuel required for combustion of the air-fuel mixture. In this regard, in the present embodiment, when the fuel pressure PF falls below the first pressure PF1 after the valve closing process is executed, the shutoff valve 40 is opened. When the shutoff valve 40 is opened, the fuel pressure PF increases and is restored. Therefore, it is possible to prevent the combustion of the air-fuel mixture from becoming difficult due to a prolonged valve closing process.

[0033] (4) The shutoff valve 40 is opened so that the fuel pressure PF is equal to or greater than the first pressure PF1 and less than the second pressure PF2. Therefore, the shutoff valve 40 is opened so that the increase in the fuel pressure PF due to the valve opening process is less than the second pressure PF2. Therefore, the execution of the valve opening process prevents the fuel pressure PF from becoming excessively high. Therefore, it is possible to prevent a deterioration in injection accuracy due to the fuel pressure PF becoming excessively high during an operating state in which the amount of fuel injected from the fuel injection valve 15 is small.

[0034] <Example of change> This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0035] In the valve opening process at S140 shown in Fig. 2, the open time of the shutoff valve 40 is determined in advance so that the increase in fuel pressure PF due to the opening of the shutoff valve 40 is less than the second pressure PF2. In addition, the difference between the fuel pressure PF after the shutoff valve 40 is opened and the second pressure PF2 is calculated. Then, the shutoff valve 40 may be closed when the calculated difference becomes equal to or less than a predetermined threshold value.

[0036] Whether the engine load of the internal combustion engine 10 is less than the predetermined load is determined based on the vehicle speed SP and the accelerator operation amount ACCP, but it may also be determined based on other parameters. For example, it may be determined based on the engine load factor KL.

[0037] The first pressure PF1 may be variably set. For example, the first pressure PF1 may be variably set so that the value of the first pressure PF1 is higher when the engine load factor KL is high than when it is low. In order to determine whether the fuel pressure PF has decreased to the first pressure PF1 as a result of the valve closing process, the process of S120 shown in FIG. 2 compares the fuel pressure PF with the first pressure PF1, but other processes may also be performed.

[0038] For example, the time elapsed since the shutoff valve 40 was closed in the process of S130 may be measured. If the measured elapsed time is equal to or greater than a predetermined time, it may be assumed that the fuel pressure PF has decreased to the first pressure PF1 due to the valve closing process, and the process of S140 may be executed.

[0039] Also, for example, an integrated value is calculated for the amount of fuel injected after the shutoff valve 40 is closed in the process of S130. If the integrated value is equal to or greater than a predetermined value, it may be assumed that the fuel pressure PF has decreased to the first pressure PF1 due to the valve closing process, and the process of S140 may be executed.

[0040] Although the gaseous fuel is hydrogen gas, other gaseous fuels, such as natural gas, may be used. The location of the shutoff valve 40 may be changed as needed. If the flow path of the fuel pipe 30 can be completely closed by completely closing the pressure reducing valve 50, the pressure reducing valve 50 may be used instead of the shut-off valve 40 as the valve that performs the valve closing process and the valve opening process.

[0041] The control device 100 includes a CPU 110 and a memory 120 and executes software processing. However, this is merely an example. The control device 100 may also include a dedicated hardware circuit (e.g., an ASIC) that processes at least part of the software processing executed in the above embodiment. That is, the control device 100 may have any of the following configurations (a) to (c): (a) a processing device that executes all of the above processing according to a program and a program storage device such as a memory that stores the program; (b) a processing device and program storage device that executes part of the above processing according to a program and a dedicated hardware circuit that executes the remaining processing; or (c) a dedicated hardware circuit that executes all of the above processing. Here, there may be multiple software circuits and dedicated hardware circuits that include a processing device and a program storage device. That is, the above processing may be executed by a processing circuit that includes at least one software circuit and one or more dedicated hardware circuits. The program storage device, i.e., computer-readable medium, includes any available medium that can be accessed by a general-purpose or dedicated computer.

[0042] <Related technical ideas> The technical ideas that can be understood from the above-described embodiment and modified examples will be described. (Appendix 1) A fuel injection control device applicable to an internal combustion engine equipped with a fuel supply device including a tank for storing gaseous fuel, a fuel injection valve for supplying fuel to a cylinder, a fuel supply passage for supplying fuel in the tank to the fuel injection valve, and a valve provided in the fuel supply passage, When the engine load of the internal combustion engine is less than a predetermined load, a valve closing process is executed to close the valve. Fuel injection control device for internal combustion engines.

[0043] (Appendix 2) the fuel supply passage is provided with a pressure reducing valve and a shutoff valve that opens and closes the fuel supply passage, The valve closing process is a process of closing the shutoff valve. 2. A fuel injection control device for an internal combustion engine according to claim 1.

[0044] (Appendix 3) After the valve closing process is executed, if the pressure of the fuel supplied to the fuel injection valve becomes lower than a predetermined pressure, a valve opening process is executed to open the valve. 10. A fuel injection control device for an internal combustion engine according to claim 1 or 2.

[0045] (Appendix 4) when the predetermined pressure is a first pressure and a lower limit value of the pressure of the fuel when the engine load is equal to or greater than the predetermined load is a second pressure, the first pressure is lower than the second pressure, The valve opening process is a process of opening the valve so that the pressure of the fuel is equal to or higher than the first pressure and lower than the second pressure. 4. A fuel injection control device for an internal combustion engine according to claim 3. [Explanation of symbols]

[0046] 10...Internal combustion engine 12...Fuel tank 15...Fuel injection valve 20...Fuel tank 30…Fuel piping 40...Shut-off valve 50...Reducing valve 60...Delivery pipe 70...Pressure sensor 71...Accelerator position sensor 72...Speed ​​sensor 100...Control device 110...CPU 120...Memory 200…Fuel supply device

Claims

1. A fuel injection control device applicable to an internal combustion engine equipped with a fuel supply device including a tank for storing gaseous fuel, a fuel injection valve for supplying fuel to a cylinder, a fuel supply passage for supplying fuel in the tank to the fuel injection valve, and a valve provided in the fuel supply passage, When the engine load of the internal combustion engine is less than a predetermined load, a valve closing process is executed to close the valve; After the valve closing process is executed, if the pressure of the fuel supplied to the fuel injection valve becomes lower than a predetermined pressure, a valve opening process is executed to open the valve. Fuel injection control device for internal combustion engines.

2. when the predetermined pressure is a first pressure and a lower limit value of the pressure of the fuel when the engine load is equal to or greater than the predetermined load is a second pressure, the first pressure is lower than the second pressure, The valve opening process is a process of opening the valve so that the pressure of the fuel is equal to or greater than the first pressure and less than the second pressure.

2. A fuel injection control device for an internal combustion engine according to claim 1.

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