Control device for internal combustion engine

Abstract

To provide a control device for an internal combustion engine capable of improving followability of fuel pressure when set fuel pressure is changed.SOLUTION: A control device 100 for an internal-combustion engine includes a decompression part 10 provided in fuel passages 7, 8 from a hydrogen cylinder 6 to an injector 9 and configured to change a set pressure of fuel, and a ECU20 for controlling a target air fuel ratio, combustion timing, and the set pressure of fuel based on a state quantity of an engine 2. When a set fuel pressure is changed from a first pressure on a high pressure side to a second pressure on a low pressure side according to a state quantity of an engine 2, a ECU20 enriches a target air fuel ratio as compared with a predetermined non-enriched state in which a fuel pressure from a pressure reducing part 10 to an injector 9 converges to the second pressure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, a fuel supply device for a compressed natural gas engine has been known that includes a high-pressure regulator and a low-pressure regulator arranged in this order from the gas cylinder side in a fuel supply passage connecting the gas cylinder and the engine, a bypass passage arranged before and after the high-pressure regulator, and an on-off valve arranged in the bypass passage (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-249075 Summary of the Invention [Problem to be solved by the invention]

[0004] In a configuration in which the set fuel pressure of the fuel pressure can be changed, as in the above-described conventional technology, when the set fuel pressure is changed, the fuel pressure in the fuel passage leading to the downstream injector does not immediately follow the changed set fuel pressure. This transient deviation of the fuel pressure from the changed set fuel pressure may affect the control of the target air-fuel ratio and combustion timing. Therefore, there is room for improvement in the follow-up of the fuel pressure when the set fuel pressure is changed.

[0005] An object of the present invention is to provide a control device for an internal combustion engine that can improve the follow-up of the fuel pressure when the set fuel pressure is changed. [Means for solving the problem]

[0006] One aspect of the present invention is a control device for an internal combustion engine that controls a target air-fuel ratio and combustion timing of the internal combustion engine, and includes a pressure reducing unit that is provided in a fuel passage from a fuel tank to an injector and is configured to be able to change a set fuel pressure of the fuel pressure, and a control unit that controls the target air-fuel ratio, combustion timing, and set fuel pressure based on state quantities of the internal combustion engine, and when the set fuel pressure is changed from a first pressure on the high-pressure side to a second pressure on the low-pressure side in accordance with the state quantities of the internal combustion engine, the control unit enriches the target air-fuel ratio compared to a predetermined non-enriched state in which the fuel pressure from the pressure reducing unit to the injector converges to the second pressure.

[0007] In a control device for an internal combustion engine according to one aspect of the present invention, when the set fuel pressure is changed from a first pressure on the high-pressure side to a second pressure on the low-pressure side, the target air-fuel ratio is enriched compared to a predetermined steady state in which the fuel pressure from the pressure reducing unit to the injector converges to the second pressure. Enriching the target air-fuel ratio promotes fuel consumption from the pressure reducing unit to the injector, so the fuel pressure decreases more quickly compared to a non-enriched state. This improves the response of the fuel pressure when the set fuel pressure is changed.

[0008] In one embodiment, when the set fuel pressure is changed from the first pressure to the second pressure in accordance with the state quantity of the internal combustion engine, the target air-fuel ratio may be enriched and the combustion timing may be retarded compared to a non-enriched state. In this case, enriching the target air-fuel ratio promotes fuel consumption from the pressure reduction section to the injector, and retarding the combustion timing can suppress an increase in output torque due to enrichment.

[0009] In one embodiment, the fuel is a gas fuel containing hydrogen, and the control unit may enrich the target air-fuel ratio by a larger amount when the rotation speed of the internal combustion engine is equal to or greater than a predetermined rotation speed threshold value compared to when the rotation speed of the internal combustion engine is less than the rotation speed threshold value. In this case, it is possible to ensure that combustion is completed and exhausted in the exhaust stroke.

[0010] In one embodiment, the control unit may acquire the fuel pressure from the pressure reducing unit to the injector, and when the acquired fuel pressure becomes equal to or less than a convergence threshold value that is smaller than the first pressure and larger than the second pressure, end enriching the target air-fuel ratio. In this case, the enrichment of the target air-fuel ratio can be automatically ended by utilizing the fact that the fuel from the pressure reducing unit to the injector is consumed and the fuel pressure decreases. [Effects of the Invention]

[0011] According to the present invention, it is possible to improve the response of the fuel pressure when the set fuel pressure is changed. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram of an internal combustion engine system including an example of a control device for an internal combustion engine. [Figure 2] 2 is a schematic diagram showing an example of the configuration of a pressure reducing unit in FIG. 1. FIG. [Figure 3] 2 is a block diagram illustrating an example of a functional configuration of the control device for the internal combustion engine of FIG. 1. [Figure 4] FIG. 4 is a diagram showing an example of injection characteristics of an injector for each set fuel pressure. [Figure 5] 5 is a timing chart showing an example of operation when the set fuel pressure is changed from a first pressure to a second pressure. [Figure 6] 2 is a flowchart showing an example of processing by the ECU in FIG. 1; [Figure 7] 7 is a flowchart showing an example of enrichment and retardation processing in FIG. 6. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0014] Fig. 1 is a schematic diagram of an internal combustion engine system including an example of a control device for an internal combustion engine. In Fig. 1, the internal combustion engine system 1 is mounted on, for example, a vehicle. The vehicle may be a passenger car or the like, or an industrial vehicle such as a forklift.

[0015] The internal combustion engine system 1 is a system for operating an engine 2 (internal combustion engine) and includes an internal combustion engine control device 100. The engine 2 is configured as, for example, a hydrogen engine that operates using gas fuel containing hydrogen (hereinafter simply referred to as "fuel" or "hydrogen") as fuel.

[0016] The internal combustion engine system 1 includes an engine 2, an intake passage 3, an air cleaner 4, a throttle valve 5, a hydrogen cylinder 6 (fuel tank), a fuel passage 7, a fuel passage 8, an injector 9, a pressure reduction section 10, an ignition plug 11, and an exhaust passage 12.

[0017] The engine 2 is, for example, a four-cylinder reciprocating engine having a cylinder head and a cylinder block.

[0018] The intake passage 3 is connected to the cylinder head of the engine 2. The intake passage 3 is a passage through which air (intake air) supplied to the engine 2 flows. An air cleaner 4 is disposed in the intake passage 3. The air cleaner 4 removes foreign matter such as dust and dirt contained in the intake air. A throttle valve 5 is disposed in the intake passage 3 between the air cleaner 4 and the cylinder head of the engine 2. The throttle valve 5 is, for example, an electromagnetic flow control valve that controls the flow rate of the intake air.

[0019] The hydrogen cylinder 6 is a fuel cylinder that stores hydrogen. The hydrogen cylinder 6 stores hydrogen in a high-pressure gas state or a liquefied state. The fuel passage 7 is a fuel passage that connects the hydrogen cylinder 6 to the pressure reduction section 10. The fuel passage 7 distributes fuel from the hydrogen cylinder 6 to the pressure reduction section 10. The fuel passage 8 is a fuel passage that connects the pressure reduction section 10 to the injector 9. The fuel passage 8 supplies fuel that has been depressurized by the pressure reduction section 10 from the pressure reduction section 10 to the injector 9. A fuel supply rail to which multiple injectors 9 are attached is connected to the end of the fuel passage 8. The fuel passages 7 and 8 can use a configuration known for hydrogen engines, and are made of materials and designed to withstand high-pressure hydrogen.

[0020] The pressure reducing unit 10 is a part that reduces the pressure of hydrogen from the hydrogen cylinder 6 to control the pressure of hydrogen supplied to the engine 2. The pressure reducing unit 10 is provided in the fuel passages 7 and 8 from the hydrogen cylinder 6 to the injector 9, and is configured to be able to change the set fuel pressure of the fuel. "Fuel pressure" refers to the pressure of the fuel from the pressure reducing unit 10 to the injector 9, and is the pressure of the fuel after it has been reduced by the pressure reducing unit 10. "Set fuel pressure" refers to the set value of the fuel pressure after the pressure of the hydrogen from the hydrogen cylinder 6 has been reduced.

[0021] Here, a first pressure P1 and a second pressure P2 lower than the first pressure P1 are set as the predetermined pressures. The pressure reducing unit 10 is configured to be able to switch the fuel pressure to either the first pressure P1 or the second pressure P2.

[0022] Fig. 2 is a schematic diagram showing an example of the configuration of the pressure reducing unit of Fig. 1. As shown in Fig. 2, pressure reducing unit 10 includes, for example, a shutoff valve 10a, a high-pressure regulator 10b, and a low-pressure regulator 10c. In pressure reducing unit 10, fuel passage 7 branches into fuel passage 7a and fuel passage 7b.

[0023] A shutoff valve 10a is connected to the fuel passage 7a downstream of the branch point with the fuel passage 7b. The shutoff valve 10a is a valve for controlling the flow of hydrogen and is configured to allow or block the flow of hydrogen. The shutoff valve 10a is, for example, a solenoid valve electrically connected to an ECU (Electronic Control Unit) 20. The shutoff valve 10a's operation of allowing or blocking the flow of hydrogen is controlled in response to an electrical signal from the ECU 20.

[0024] A high-pressure regulator 10b is connected downstream of the shut-off valve 10a. The high-pressure regulator 10b reduces the pressure of hydrogen from the hydrogen cylinder 6 to a first pressure P1. A spring-biased valve element may be provided inside the high-pressure regulator 10b so that the fuel pressure becomes the first pressure P1. A fuel passage 8a is connected downstream of the high-pressure regulator 10b. The fuel passage 8a merges with the fuel passage 8.

[0025] A low-pressure regulator 10c is connected to the fuel passage 7b branching off from the fuel passage 7a. The low-pressure regulator 10c is a regulator that reduces the pressure of hydrogen from the hydrogen cylinder 6 to a second pressure P2. A spring-biased valve element may be provided inside the low-pressure regulator 10c so that the fuel pressure becomes the second pressure P2. A fuel passage 8b is connected downstream of the low-pressure regulator 10c. The fuel passage 8b merges with the fuel passage 8. The low-pressure regulator 10c may be configured to reduce the fuel pressure below the second pressure P2 when the engine 2 is idling.

[0026] The injector 9 is an electromagnetic fuel injection valve that supplies hydrogen from the hydrogen cylinder 6 to the engine 2. The injector 9 injects gas fuel between the throttle valve 5 and the engine 2 in the intake passage 3. Note that the injector 9 may also inject gas fuel directly into the cylinders of the engine 2.

[0027] The spark plug 11 is attached to the cylinder head of the engine 2 and ignites a mixture of fuel and air drawn into the cylinder of the engine 2, thereby igniting the fuel.

[0028] The exhaust passage 12 is connected to the cylinder head of the engine 2. The exhaust passage 12 is a passage through which combustion gas generated when a mixture of intake air and gas fuel is burned in a combustion chamber of the engine 2 flows.

[0029] The control device 100 for an internal combustion engine controls the target air-fuel ratio and combustion timing of the engine 2. FIG. 3 is a block diagram illustrating the functional configuration of the control device for an internal combustion engine of FIG. 1. As shown in FIGS. 1 to 3, the control device 100 for an internal combustion engine includes a pressure reducing unit 10, a fuel pressure sensor 13, an intake pressure sensor 14, a rotation speed sensor 15, and an ECU 20 (control unit). The ECU 20 is electrically connected to the throttle valve 5, the injector 9, the spark plug 11, the pressure reducing unit 10, and the sensors 13 to 15.

[0030] The fuel pressure sensor 13 is a pressure detection unit that acquires the fuel pressure from the pressure reducing unit 10 to the injector 9. As an example, the fuel pressure sensor 13 detects the fuel pressure of hydrogen in a fuel supply rail to which multiple injectors 9 are attached.

[0031] The intake pressure sensor 14 is a pressure sensor that detects the pressure of the intake air inside the intake passage 3. The rotation speed sensor 15 is a sensor that detects the rotation speed of the engine 2.

[0032] The ECU 20 is an electronic control unit that controls the engine 2. The ECU 20 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a CAN (Controller Area Network) communication circuit, and the like. The ECU 20 realizes various functions by, for example, loading a program stored in the ROM into the RAM and executing the program loaded into the RAM with the CPU. The ECU 20 may be composed of multiple electronic control units.

[0033] The ECU 20 executes predetermined processing based on the detected values ​​of the fuel pressure sensor 13, the intake pressure sensor 14, and the rotation speed sensor 15, and controls the throttle valve 5, the injector 9, the spark plug 11, and the pressure reducing unit 10. The ECU 20 controls, for example, the opening of the throttle valve 5 based on the accelerator opening detected by an accelerator opening sensor (not shown).

[0034] The ECU 20 controls the target air-fuel ratio, combustion timing, and set fuel pressure based on engine state quantities (state quantities of the internal combustion engine). The ECU 20 has, as its functional components, an engine state quantity acquisition unit 21, a fuel injection control unit 22, and a combustion timing control unit 23.

[0035] The engine state quantity acquisition unit 21 acquires the fuel pressure, the intake air amount, and the rotation speed of the engine 2 as engine state quantities based on the detected values ​​of the fuel pressure sensor 13, the intake pressure sensor 14, and the rotation speed sensor 15.

[0036] The fuel injection control unit 22 calculates the fuel injection amount of the engine 2, for example, according to the rotation speed and required torque of the engine 2. The fuel injection amount is the amount of fuel injected by each injector 9. The fuel injection control unit 22 calculates the required torque based on the accelerator opening and the rotation speed of the engine 2, for example, using a pre-stored map with the accelerator opening and the rotation speed of the engine 2 as axes. The fuel injection control unit 22 calculates a target air-fuel ratio in normal operation, for example, using a pre-stored map with the required torque and the rotation speed of the engine 2 as axes, and calculates the fuel injection amount from the target air-fuel ratio and the intake air amount.

[0037] The target air-fuel ratio under normal conditions is a target air-fuel ratio in a predetermined non-enriched state. The predetermined non-enriched state refers to a target air-fuel ratio used during steady operation or the like, and is a state in which temporary enrichment is not performed. Temporary enrichment includes temporary enrichment for improving the tracking of the fuel pressure when the set fuel pressure is changed. Temporary enrichment may also include enrichment that is temporarily performed from the perspective of exhaust purification or the like.

[0038] The fuel injection control unit 22 switches the set fuel pressure between the first pressure P1 and the second pressure P2, for example, in accordance with the required torque.

[0039] FIG. 4 is a diagram showing an example of the injection characteristics of the injector for each set fuel pressure. In FIG. 4, the horizontal axis represents the valve opening time of the injector 9, and the vertical axis represents the required torque and the fuel injection amount in a predetermined non-enriched state corresponding to the required torque. The dashed-dotted line L10 represents the injection characteristics of the injector when the regulator through which hydrogen flows in the pressure reduction unit 10 is the high-pressure regulator 10b. The thick solid line L11 represents the injection characteristics of the injector corresponding to the valve opening period T1-T2 of the injector 9 that can be used when the regulator through which hydrogen flows in the pressure reduction unit 10 is the high-pressure regulator 10b. Q11 is the minimum value of the fuel injection amount for the injection characteristics of the thick solid line L11. Tq11 is the minimum value of the required torque at which the fuel injection amount in a predetermined non-enriched state becomes Q11. Q12 is the maximum value of the fuel injection amount for the injection characteristics of the thick solid line L11. Tq12 is the maximum value of the required torque at which the fuel injection amount in a predetermined non-enriched state becomes Q12.

[0040] In FIG. 4, the dashed dotted line L20 indicates the injection characteristics of the injector when the regulator through which hydrogen flows in the pressure reduction section 10 is the low-pressure regulator 10c. The thick solid line L21 indicates the injection characteristics of the injector corresponding to the valve opening period T1 to T2 of the injector 9 that can be used when the regulator through which hydrogen flows in the pressure reduction section 10 is the low-pressure regulator 10c. Q21 is the minimum value of the fuel injection amount for the injection characteristics of the thick solid line L21. Tq21 is the minimum value of the required torque at which the fuel injection amount becomes Q21 in a predetermined non-enriched state. Q22 is the maximum value of the fuel injection amount for the injection characteristics of the thick solid line L21. Tq22 is the maximum value of the required torque at which the fuel injection amount becomes Q22 in a predetermined non-enriched state.

[0041] In FIG. 4, threshold value Tqth is a threshold value of the required torque for switching between the high-pressure regulator 10b and the low-pressure regulator 10c. Threshold value Tqth is a value of the required torque such that the fuel injection amount in a predetermined non-enriched state becomes Qth. Qth is a value of the fuel injection amount at which switching between the high-pressure regulator 10b and the low-pressure regulator 10c is performed. Qth can be a value of the fuel injection amount included in the range where the fuel injection amount according to the injection characteristic of the thick solid line L11 and the fuel injection amount according to the injection characteristic of the thick solid line L21 overlap each other. Qth is, for example, smaller than Q22 and larger than Q11. Qth may be equal to either Q11 or Q22. Considering that the valve opening period T1-T2 of the injector 9 available in terms of the hardware requirements of the injector 9 varies depending on the rotation speed of the engine 2, threshold value Tqth may be a map value corresponding to the rotation speed of the engine 2.

[0042] For example, when the required torque becomes equal to or greater than the threshold value Tqth, the fuel injection control unit 22 switches the regulator through which hydrogen flows in the pressure reducing unit 10 from the low-pressure regulator 10c to the high-pressure regulator 10b. As a result, the pressure of fuel supplied to the injector 9 becomes higher than when the regulator through which hydrogen flows is the low-pressure regulator 10c, and therefore the fuel injection amount increases even if the valve opening period (injection period) is the same.

[0043] For example, when the required torque becomes less than the threshold value Tqth, the fuel injection control unit 22 switches the regulator through which hydrogen flows in the pressure reducing unit 10 from the high-pressure regulator 10b to the low-pressure regulator 10c. As a result, the supply pressure of fuel to the injector 9 becomes lower than when the regulator through which hydrogen flows is the high-pressure regulator 10b, and therefore the fuel injection amount decreases even if the valve opening period (injection period) is the same.

[0044] Furthermore, when the required torque changes from less than the threshold Tqth to equal to or greater than the threshold Tqth, the fuel injection control unit 22 may change the valve opening period of the injector 9 from the valve opening period in which the fuel injection amount is Qth on the thick solid line L21 to the valve opening period in which the fuel injection amount is Qth on the thick solid line L11. Conversely, when the required torque changes from equal to or greater than the threshold Tqth to less than the threshold Tqth, the fuel injection control unit 22 may change the valve opening period of the injector 9 from the valve opening period in which the fuel injection amount is Qth on the thick solid line L11 to the valve opening period in which the fuel injection amount is Qth on the thick solid line L21.

[0045] By combining the injection characteristics of the high-pressure regulator 10b and the injection characteristics of the low-pressure regulator 10c in this way, it is possible to widen the range between the upper and lower limits of the fuel injection amount for the same injector 9 as hardware, without adding an injector, for example. Note that the fuel injection control unit 22 may provide a predetermined hysteresis in the comparison between the required torque and the threshold value Tqth.

[0046] Furthermore, in the control device 100 for an internal combustion engine according to the present disclosure, when the fuel injection control unit 22 changes the set fuel pressure from a first pressure P1 on the high pressure side to a second pressure P2 on the low pressure side in accordance with the engine state quantity, the fuel injection control unit 22 enriches the target air-fuel ratio compared to a predetermined non-enriched state when the fuel pressure from the pressure reducing unit 10 to the injector 9 converges to the second pressure P2.

[0047] Figure 5 is a timing chart showing an example of operation when the set fuel pressure is changed from a first pressure to a second pressure. In Figure 5, the horizontal axis represents time, and the vertical axis represents the fuel pressure from pressure reduction unit 10 to injector 9. In Figure 5, at time t10, the regulator through which hydrogen flows in pressure reduction unit 10 is high-pressure regulator 10b. At time t11, the regulator through which hydrogen flows in pressure reduction unit 10 is switched from high-pressure regulator 10b to low-pressure regulator 10c.

[0048] In the example of Fig. 5, the two-dot chain line L31 is a comparative example showing the time-series change in fuel pressure when the target air-fuel ratio is in a predetermined non-enriched state. As shown by the two-dot chain line L31, when the set fuel pressure is changed from the first pressure P1 to the second pressure P2 at time t11, the actual fuel pressure does not immediately follow the second pressure P2, which is the set fuel pressure after the change, because the fuel passage 8 downstream of the pressure reducing unit 10 and the injector 9 have a certain volume. In the example of Fig. 5, the actual fuel pressure decreases to and converges to the second pressure P2 after time t13.

[0049] In contrast, solid line L30 is an example showing a time-series change in fuel pressure when the target air-fuel ratio is enriched compared to a predetermined non-enriched state. As shown by solid line L30, when the set fuel pressure is changed from the first pressure P1 to the second pressure P2 at time t11, the fuel injection control unit 22 sets the target air-fuel ratio so as to be enriched compared to the predetermined non-enriched state. In other words, the target λ is changed to be richer than normal. The degree of enrichment of the target air-fuel ratio is stored in the ECU 20 as a parameter or map value determined in advance based on test results or simulation results that take into account, for example, whether or not the combustion timing is retarded, the combustion limit in the engine 2, and the output torque characteristics relative to the combustion timing, as described below.

[0050] Because the target air-fuel ratio is enriched compared to a predetermined non-enriched state, each time the injector 9 injects fuel after time t11, a larger amount of fuel is injected compared to when the target air-fuel ratio is not enriched. This promotes consumption of the fuel remaining in the fixed volume from the pressure reducing section 10 to the injector 9 with the first pressure P1 as the residual pressure. As a result, the fuel pressure indicated by the solid line L30 in Figure 5 decreases more quickly than the two-dot chain line L31, and remains at a pressure lower than the two-dot chain line L31 in the non-enriched state.

[0051] Incidentally, when the rotation speed of the engine 2 is equal to or higher than a predetermined rotation speed threshold, the fuel injection control unit 22 may enrich the target air-fuel ratio by a larger amount of change than when the rotation speed of the engine 2 is lower than the rotation speed threshold. The rotation speed threshold is a threshold value for the rotation speed of the engine 2 for enriching the target air-fuel ratio on the high rotation speed side according to the rotation speed of the engine 2. The rotation speed threshold may be a predetermined parameter or may be a substantial threshold value in a map. The substantial threshold value in a map means that when the degree of enrichment of the target air-fuel ratio is set as a map value based on, for example, the rotation speed of the engine 2, the map value on the high rotation speed side at map points of adjacent rotation speeds of the engine 2 is enriched to a greater degree than the map value on the low rotation speed side, and thus a substantial rotation speed threshold exists within the range of the rotation speeds of the adjacent engines 2.

[0052] The fuel injection control unit 22 acquires the fuel pressure from the pressure reducing unit 10 to the injector 9 based on the detection result of the fuel pressure sensor 13. When the acquired fuel pressure becomes equal to or less than a threshold pressure Pth (convergence threshold), the fuel injection control unit 22 ends enriching the target air-fuel ratio.

[0053] The threshold pressure Pth is a fuel pressure threshold for determining whether to end enrichment of the target air-fuel ratio. The threshold pressure Pth is smaller than the first pressure P1 and larger than the second pressure P2. The threshold pressure Pth may be set to a fuel pressure value close enough to the second pressure P2 to improve the response of the fuel pressure when the set fuel pressure is changed.

[0054] The fuel pressure indicated by the solid line L30 in Fig. 5 corresponds to the case where the fuel pressure has decreased to the threshold pressure Pth at time t12 and is equal to or lower than the threshold pressure Pth. If enrichment of the target air-fuel ratio is completed in the period from time t12 to time t13 in Fig. 5, the fuel pressure indicated by the solid line L30 may decrease at the same gradient as the two-dot chain line L31 in the non-enriched state.

[0055] The combustion timing control unit 23 controls the combustion timing of the engine 2, for example, in accordance with the rotational speed and required torque of the engine 2. For example, if the engine 2 is a spark-ignition internal combustion engine, the combustion timing is the ignition timing of the spark plug 11. The combustion timing control unit 23 may calculate the ignition timing based on the accelerator opening and the rotational speed of the engine 2, for example, by using a pre-stored map that uses the accelerator opening and the rotational speed of the engine 2 as axes.

[0056] The ignition timing may be the ignition timing of the combustion timing that outputs, at a target air-fuel ratio in normal times, a required torque that has not been particularly corrected in accordance with the accelerator opening and the rotation speed of the engine 2. The ignition timing may be the ignition timing of the combustion timing that outputs, at a target air-fuel ratio in normal times, a required torque that reflects a correction torque that has been calculated separately for a reference torque that has not been particularly corrected in accordance with the accelerator opening and the rotation speed of the engine 2.

[0057] When the fuel injection control unit 22 and the combustion timing control unit 23 change the set fuel pressure from the first pressure P1 to the second pressure P2 in accordance with the engine state quantity, they enrich the target air-fuel ratio compared to a predetermined non-enriched state and retard the combustion timing.

[0058] For example, when the target air-fuel ratio is enriched by the fuel injection control unit 22 compared to a predetermined non-enriched state, the combustion timing control unit 23 retards the combustion timing so as to offset the increase in output torque resulting from enriching the target air-fuel ratio. In other words, the amount of decrease in output torque due to retarding the combustion timing may be the same as the amount of increase in output torque resulting from enriching the target air-fuel ratio.

[0059] The degree of retardation of the combustion timing is stored in the ECU 20 as a parameter or a map value that is determined in advance based on test results or simulation results that take into account the combustion limit of the engine 2 and the output torque characteristics relative to the combustion timing. The degree of retardation of the combustion timing may be set so as to prioritize not exceeding the combustion limit of the engine 2 over a decrease in the output torque.

[0060] The fuel injection control unit 22 and the combustion timing control unit 23 may acquire the fuel pressure from the pressure reducing unit 10 to the injector 9, and when the acquired fuel pressure becomes equal to or lower than the threshold pressure Pth, may terminate enrichment of the target air-fuel ratio and terminate retardation of the combustion timing.

[0061] Next, an example of the processing of the control device 100 for an internal combustion engine will be described with reference to the flowcharts of Figures 6 and 7. Figure 6 is a flowchart showing an example of the processing of the ECU of Figure 1. Figure 7 is a flowchart showing an example of the enrichment and retardation processing of Figure 6. The processing of the flowcharts shown in Figures 6 and 7 is repeatedly executed at predetermined calculation intervals while the engine 2 is operating, for example.

[0062] 6, in S01, the ECU 20 of the control device 100 for an internal combustion engine calculates the required torque using the fuel injection control unit 22. The fuel injection control unit 22 calculates the required torque based on, for example, the accelerator opening and the rotation speed of the engine 2.

[0063] In S02, the ECU 20 determines whether the set fuel pressure has been changed from a first pressure on the high-pressure side to a second pressure on the low-pressure side by the fuel injection control unit 22. For example, when the required torque becomes less than the threshold value Tqth, the fuel injection control unit 22 switches the regulator through which hydrogen flows in the pressure reducing unit 10 from the high-pressure regulator 10b to the low-pressure regulator 10c. When the required torque is less than the threshold value Tqth, the fuel injection control unit 22 may determine that the set fuel pressure has been changed from the first pressure to the second pressure.

[0064] If the set fuel pressure has been changed from the first pressure to the second pressure (S02: YES), the ECU 20 proceeds to the process of S03. If the set fuel pressure has not been changed from the first pressure to the second pressure (S02: NO), the ECU 20 proceeds to the process of S04.

[0065] In S03, the ECU 20 enriches the target air-fuel ratio and retards the combustion timing using the fuel injection control unit 22 and the combustion timing control unit 23. The fuel injection control unit 22 sets the target air-fuel ratio so as to be richer than a predetermined non-enriched state. The combustion timing control unit 23 retards the combustion timing, for example, to offset the increase in output torque resulting from enriching the target air-fuel ratio.

[0066] Meanwhile, in S04, the ECU 20 sets the target air-fuel ratio and combustion timing according to a predetermined non-enriched state by the fuel injection control unit 22 and the combustion timing control unit 23. The fuel injection control unit 22 may set the target air-fuel ratio so as to achieve the predetermined non-enriched state. The combustion timing control unit 23 may set the ignition timing of the combustion timing that outputs a required torque that is not particularly corrected according to the accelerator opening and the rotation speed of the engine 2. Thereafter, the ECU 20 ends the processing of FIG. 6.

[0067] Specifically, the process of S03 is executed and terminated as shown in FIG.

[0068] 7, in S11, the ECU 20 of the control device 100 for an internal combustion engine executes enriched fuel injection and retarded combustion using the fuel injection control unit 22 and the combustion timing control unit 23. The fuel injection control unit 22 and the combustion timing control unit 23 control the valve opening period of the injector 9 and the ignition timing of the spark plug 11, for example, to achieve enriched fuel injection and retarded combustion.

[0069] In S12, the ECU 20 acquires the fuel pressure using the fuel injection control unit 22. The fuel injection control unit 22 acquires the fuel pressure from the pressure reducing unit 10 to the injector 9 based on the detection result of the fuel pressure sensor 13, for example.

[0070] In S13, the ECU 20 determines whether the fuel pressure has become equal to or less than the convergence threshold value using the fuel injection control unit 22. The fuel injection control unit 22 determines whether the acquired fuel pressure has become equal to or less than the threshold pressure Pth (convergence threshold value). If the fuel pressure has become equal to or less than the convergence threshold value (S13: YES), the ECU 20 proceeds to the process of S14. If the fuel pressure has not become equal to or less than the convergence threshold value (S13: NO), the ECU 20 returns to the process of S11 and repeats the processes of S11 to S13.

[0071] In S14, the ECU 20 causes the fuel injection control unit 22 and the combustion timing control unit 23 to end enriching the target air-fuel ratio and end retarding the combustion timing. The fuel injection control unit 22 may set the target air-fuel ratio to a predetermined non-enriched state. The combustion timing control unit 23 may set the ignition timing of the combustion timing to output a required torque that is not particularly corrected according to the accelerator opening and the rotation speed of the engine 2. Thereafter, the ECU 20 ends the processing of FIG. 7, returns to FIG. 6, and ends the processing of FIG. 6.

[0072] [Action and effect] In the control device 100 for an internal combustion engine configured as described above, when the set fuel pressure is changed from the first pressure P1 on the high-pressure side to the second pressure P2 on the low-pressure side, the target air-fuel ratio is enriched compared to a predetermined steady state in which the fuel pressure from the pressure reduction unit 10 to the injector 9 converges to the second pressure P2. Enriching the target air-fuel ratio promotes fuel consumption from the pressure reduction unit 10 to the injector 9, so the fuel pressure decreases more quickly compared to a non-enriched state. This makes it possible to improve the response of the fuel pressure when the set fuel pressure is changed.

[0073] In the control device 100 for an internal combustion engine, when the set fuel pressure is changed from the first pressure P1 to the second pressure P2 in accordance with the engine state quantity, the target air-fuel ratio is enriched compared to a non-enriched state, and the combustion timing is retarded. As a result, enriching the target air-fuel ratio promotes fuel consumption from the pressure reducing section 10 to the injector 9, and retarding the combustion timing can suppress an increase in output torque due to enrichment.

[0074] In the control device 100 for an internal combustion engine, the fuel is a gas fuel containing hydrogen, and the ECU 20 enriches the target air-fuel ratio by a larger amount when the rotation speed of the engine 2 is equal to or greater than a predetermined rotation speed threshold compared to when the rotation speed of the engine 2 is less than the rotation speed threshold. Here, in an engine 2 fueled by a gas fuel containing hydrogen, it is desirable to complete combustion and exhaust the fuel in the combustion stroke and exhaust stroke in order to suppress hydrogen from remaining in the cylinder. However, when the combustion timing is retarded, the start of combustion is delayed and the combustion speed decreases, while the time until the exhaust valve closes becomes shorter as the rotation speed of the engine 2 increases. Therefore, by increasing the enrichment when the rotation speed of the engine 2 is equal to or greater than a predetermined rotation speed threshold, the combustion speed can be increased, ensuring that combustion is completed and exhausted in the exhaust stroke.

[0075] In the control device 100 for an internal combustion engine, the ECU 20 acquires the fuel pressure from the pressure reducing unit 10 to the injector 9, and terminates enrichment of the target air-fuel ratio when the acquired fuel pressure becomes equal to or less than a threshold pressure Pth (convergence threshold) that is smaller than the first pressure P1 and larger than the second pressure P2. This makes it possible to automatically terminate enrichment of the target air-fuel ratio by utilizing the fact that the fuel from the pressure reducing unit 10 to the injector 9 is consumed and the fuel pressure decreases.

[0076] [Variations] The present invention is not limited to the above-described embodiment, and can be embodied in various forms including the above-described embodiment and various modifications and improvements based on the knowledge of those skilled in the art.

[0077] In the above embodiment, the pressure reducing unit 10 includes the shutoff valve 10a, the high-pressure regulator 10b, and the low-pressure regulator 10c, but is not limited to this example. The pressure reducing unit may be, for example, (1) a configuration in which regulators are provided in parallel and the passage switches in a single step from a first pressure on the high-pressure side to a second pressure on the low-pressure side, (2) a configuration in which regulators are provided in series so that the second pressure on the low-pressure side is reached at the most downstream side and the first pressure on the high-pressure side is reached by bypassing the downstream regulator, and the bypass flow is suddenly shut off, or (3) a configuration in which the regulator is configured to continuously change the pressure and changes the pressure to the low-pressure side faster than the pressure tracking speed in the fuel passage 8.

[0078] In the above embodiment, the fuel injection control unit 22 and the combustion timing control unit 23 enrich the target air-fuel ratio and retard the combustion timing, but retarding the combustion timing is not essential. For example, the increase in output torque resulting from enriching the target air-fuel ratio may be utilized by increasing the load on an auxiliary device such as a generator, or may be offset by regenerating the torque in the traction motor.

[0079] In the above embodiment, the fuel injection control unit 22 acquires the fuel pressure from the pressure reducing unit 10 to the injector 9, and terminates enriching the target air-fuel ratio when the acquired fuel pressure becomes equal to or less than the threshold pressure Pth (convergence threshold) that is smaller than the first pressure P1 and larger than the second pressure P2, but is not limited to this example. For example, the enrichment of the target air-fuel ratio may be performed for a predetermined duration that is set in advance by simulation, testing, or the like, and terminated after the duration has elapsed.

[0080] In the above embodiment, the fuel pressure sensor 13 detects the fuel pressure in the fuel supply rail, but it may also detect the fuel pressure in the fuel passage 8 other than the fuel supply rail.

[0081] In the above embodiment, the fuel injection control unit 22 acquires the fuel pressure from the pressure reducing unit 10 to the injector 9 based on the detection result of the fuel pressure sensor 13, but the present invention is not limited to this example. The fuel injection control unit 22 may estimate and acquire the fuel pressure from the pressure reducing unit 10 to the injector 9 using the volume value of the fuel passage 8 from the pressure reducing unit 10 to the injector 9 and the volume equivalent value of the fuel injected by the injector 9 in the fuel passage 8.

[0082] In the above embodiment, a gas fuel containing hydrogen is used as the fuel, but this is not limiting. The fuel may be a gas fuel other than hydrogen, or a liquid fuel such as gasoline or diesel. Furthermore, the combustion timing to be retarded may be the ignition timing of gas in the cylinder when the internal combustion engine does not use spark ignition, such as when the internal combustion engine is a diesel or HCCI engine.

[0083] 5 of the above embodiment, the degree of enrichment of the target air-fuel ratio may be reduced without terminating the enrichment in the period from time t12 to time t13. In this case, the fuel pressure indicated by the solid line L30 may decrease at a slope greater than that of the two-dot chain line L31 in the non-enriched state and at a slope smaller than that of the solid line L30 in the period from time t11 to time t12.

[0084] In the above embodiment, the intake air amount is detected using the intake pressure sensor 14, but the intake air amount may also be detected by, for example, an air flow sensor or the like. [Explanation of symbols]

[0085] 2...engine (internal combustion engine), 6...hydrogen cylinder (fuel tank), 7, 7a, 7b, 8, 8a, 8b...fuel passage, 9...injector, 10...pressure reduction section, 20...ECU (control section), 100...control device for internal combustion engine, P1...first pressure, P2...second pressure, Pth...threshold pressure (convergence threshold).

Claims

1. A control device for an internal combustion engine that controls a target air-fuel ratio and combustion timing of the internal combustion engine, a pressure reducing unit provided in a fuel passage from a fuel tank to an injector, the pressure reducing unit being configured to be able to change a set fuel pressure of the fuel; a control unit that controls the target air-fuel ratio, the combustion timing, and the set fuel pressure based on state quantities of the internal combustion engine, a control device for an internal combustion engine, wherein when the set fuel pressure is changed from a first pressure on the high pressure side to a second pressure on the low pressure side in accordance with a state quantity of the internal combustion engine, the control unit enriches the target air-fuel ratio compared to a predetermined non-enriched state in which the fuel pressure from the pressure reducing unit to the injector converges to the second pressure.

2. 2. The control device for an internal combustion engine according to claim 1, wherein, when the set fuel pressure is changed from the first pressure to the second pressure in accordance with a state quantity of the internal combustion engine, the control unit enriches the target air-fuel ratio compared to the non-enriched state and retards the combustion timing.

3. the fuel is a gas fuel containing hydrogen, 3. The control device for an internal combustion engine according to claim 2, wherein the control unit enriches the target air-fuel ratio by a larger amount of change when the rotation speed of the internal combustion engine is equal to or greater than a predetermined rotation speed threshold value compared to when the rotation speed of the internal combustion engine is less than the rotation speed threshold value.

4. 3. The control device for an internal combustion engine according to claim 1, wherein the control unit acquires the fuel pressure from the pressure reducing unit to the injector, and when the acquired fuel pressure becomes equal to or less than a convergence threshold value that is smaller than the first pressure and larger than the second pressure, ends enriching the target air-fuel ratio.

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