fuel injection device

Abstract

The present invention provides a fuel injection system that can suppress fluctuations in output torque caused by variations in the amount of fuel injected into each cylinder. [Solution] The fuel injection system 50 includes an injector 51 provided for each of the multiple cylinders 11 of the internal combustion engine 10 to inject fuel into the cylinder 11, and a control device 100 that controls the fuel injection by the injector 51. The control device 100 performs partial lift injection multiple times in one combustion cycle, injecting fuel when the needle valve of the injector 51 has not reached the full lift position. When the amount of fluctuation in the output torque of the internal combustion engine 10 is greater than or equal to a predetermined torque value, the control device 100 performs full lift injection at least once among the multiple fuel injections, injecting fuel when the needle valve of the injector 51 has reached the full lift position.

Description

Technical Field

[0001] The present disclosure relates to a fuel injection device that injects fuel into a cylinder of an internal combustion engine.

Background Art

[0002] The internal combustion engine disclosed in Patent Document 1 includes a fuel injection device. The fuel injection device executes multiple fuel injections in one combustion cycle of the internal combustion engine.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When multiple fuel injections are executed in one combustion cycle, the injection amount per injection decreases as the number of injections increases. When the injection amount per injection decreases, the fuel is likely to vaporize, so the exhaust characteristics are less likely to deteriorate. However, when the injection amount per injection decreases, the injection amount for each cylinder is likely to vary, so the output torque of the internal combustion engine may fluctuate greatly.

Means for Solving the Problems

[0005] A fuel injection system for solving the above problems comprises an injector provided for each of the multiple cylinders of an internal combustion engine for injecting fuel into the cylinder, and a control device for controlling the fuel injection by the injector, wherein the control device performs partial lift injection multiple times in one combustion cycle, in which fuel is injected when the needle valve of the injector has not reached the full lift position, and when the amount of fluctuation in the output torque of the internal combustion engine is greater than or equal to a predetermined torque value, at least one of the multiple fuel injections is performed as a full lift injection, in which fuel is injected when the needle valve of the injector has reached the full lift position.

[0006] According to the above configuration, the control device performs full-lift injection at least once when the amount of fluctuation in output torque exceeds a predetermined value. Compared to partial-lift injection, full-lift injection has less variation in the amount of fuel injected per injection. Therefore, compared to the case where all fuel injections are partial-lift injections, performing at least one full-lift injection results in less variation in the amount of fuel injected per cylinder. As a result, the amount of fluctuation in the output torque of the internal combustion engine is less likely to increase. [Effects of the Invention]

[0007] The fuel injection system of this disclosure can suppress fluctuations in output torque caused by variations in the amount of fuel injected into each cylinder. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of an internal combustion engine having a fuel injection system according to an embodiment. [Figure 2] Figure 1 is a schematic diagram illustrating a first example of fuel injection timing by the fuel injection device. [Figure 3] This is a schematic diagram illustrating a second example of the fuel injection timing by the fuel injection device shown in Figure 1. [Figure 4] This is a flowchart showing the first part of the injection control process performed by the control device shown in Figure 1. [Figure 5]This flowchart shows the second part of the injection control process performed by the control device shown in Figure 1. [Modes for carrying out the invention]

[0009] <Overall Configuration of an Internal Combustion Engine> An embodiment of the internal combustion engine 10 will be described with reference to Figures 1 to 5. As shown in Figure 1, the vehicle is equipped with an internal combustion engine 10. The internal combustion engine 10 is the power source of the vehicle. The internal combustion engine 10 is equipped with a plurality of cylinders 11. Only one of the plurality of cylinders 11 is shown in Figure 1. A cylinder 11 is a space for burning a mixture of fuel and intake air. In this embodiment, there are four cylinders 11.

[0010] Each cylinder 11 is equipped with a piston 12 that is capable of reciprocating motion. The piston 12 is connected to the crankshaft 14 via a connecting rod 13. A connecting rod 13 and a crankshaft 14 are provided for each set of cylinders 11. The piston 12 reciprocates within the cylinder 11 in a direction along the central axis of the piston 12. The crankshaft 14 rotates in accordance with the reciprocating motion of the piston 12. The piston 12 operates between a top dead center, which is furthest from the crankshaft 14, and a bottom dead center, which is closest to the crankshaft 14. Hereinafter, the direction in which the piston 12 moves toward the top dead center will be referred to as upward, and the opposite direction will be referred to as downward. Of the two end faces of the piston 12 in the direction along the central axis, the end face facing upward will be referred to as the top face 12A.

[0011] The internal combustion engine 10 is equipped with multiple spark plugs 15. Figure 1 shows only one of the multiple spark plugs 15. A spark plug 15 is provided for each of the multiple cylinders 11. The tip of the spark plug 15 is located inside the cylinder 11. The spark plug 15 ignites the fuel-air mixture inside the cylinder 11.

[0012] The internal combustion engine 10 is equipped with an intake passage 20. The intake passage 20 is a passage for introducing intake air into each cylinder 11. The intake passage 20 is connected to each cylinder 11. A throttle valve 21 is positioned in the middle of the intake passage 20. The throttle valve 21's opening degree is adjustable. Therefore, the amount of intake air changes according to the opening degree of the throttle valve 21.

[0013] The internal combustion engine 10 is equipped with an exhaust passage 30. The exhaust passage 30 is a passage for discharging exhaust gas from each cylinder 11. The exhaust passage 30 is connected to each cylinder 11. A catalyst and a filter, etc., are arranged in the exhaust passage 30 for purifying and collecting harmful substances contained in the exhaust gas.

[0014] The internal combustion engine 10 is a four-stroke, one-cycle engine. One cycle of the internal combustion engine 10 consists of the intake stroke, compression stroke, combustion stroke, and exhaust stroke in each cylinder 11, which completes when the crankshaft 14 rotates 720 degrees. The intake stroke is the period when the piston 12 moves from top dead center to bottom dead center in a given cylinder 11. The compression stroke is the period when the piston 12 moves from bottom dead center to top dead center, following the intake stroke. The combustion stroke is the period when the piston 12 moves from top dead center to bottom dead center, following the compression stroke. The exhaust stroke is the period when the piston 12 moves from bottom dead center to top dead center, following the combustion stroke. After the combustion stroke, the intake stroke of the next cycle begins.

[0015] The vehicle is equipped with a fuel injection system 50. The fuel injection system 50 comprises an injector 51 and a control device 100. An injector 51 is provided for each of the multiple cylinders 11 of the internal combustion engine 10. Figure 1 shows only one of the multiple injectors 51. The injector 51 is located above the piston 12 relative to the cylinder 11. The tip of the injector 51 is located inside the cylinder 11. The tip of the injector 51 is located above the top dead center of the piston 12. The injection nozzle 52 provided at the tip of the injector 51 faces the top surface 12A of the piston 12.

[0016] During the intake stroke, the piston 12 moves from the top dead center to the bottom dead center. Therefore, as the piston 12 moves from the top dead center to the bottom dead center, the distance between the injection port 52 and the piston 12 increases. For example, when fuel is injected twice during the intake stroke, the distance from the injection port 52 to the piston 12 is longer for the second injection than for the first injection. Thus, it is more difficult for fuel to adhere to the top surface 12A of the piston 12 during the second injection than during the first injection.

[0017] The injector 51 injects fuel into the cylinder 11. The injector 51 performs fuel injection from the top dead center side of the piston 12 into the cylinder 11. The injector 51 injects fuel directly into the cylinder 11 without passing through the intake passage 20. The injector 51 injects, for example, gasoline as fuel. The internal combustion engine 10 includes a fuel pump 16 that supplies fuel to the injector 51. The fuel injection pressure, which is the fuel pressure injected from the injector 51, is determined by the supply pressure of the fuel supplied from the fuel pump 16 to the injector 51. When injecting the same amount of fuel, the lower the fuel injection pressure of the injector 51, the longer the injection time. When the injection time is the same, the lower the fuel injection pressure of the injector 51, the smaller the fuel injection amount.

[0018] The internal combustion engine 10 includes a crank angle sensor 61 and an air flow meter 62. The crank angle sensor 61 detects the crank angle, which is the rotation angle of the crankshaft 14. The air flow meter 62 detects the intake air amount. The crank angle sensor 61 and the air flow meter 62 repeatedly transmit signals corresponding to the detected information to the control device 100.

[0019] <Partial Lift Control and Full Lift Control> The control device 100 controls the fuel injection by the injector 51. The control device 100 controls the injector 51 to execute full-lift injection or partial-lift injection. Hereinafter, partial-lift is abbreviated as "PL" and full-lift as "FL" respectively. In FL injection, the injector 51 injects fuel in a state where the needle valve of the injector 51 reaches the full-lift position. That is, in FL injection, the injector 51 injects fuel during the period from when the needle valve separates from the valve seat of the injector 51 until it reaches the full-lift position, during the period when the needle valve is in the full-lift position, and during the period from the full-lift position until the needle valve seats on the valve seat. The full-lift position is the position of the needle valve when the needle valve of the injector 51 is farthest from the injection port 52.

[0020] In PL injection, the injector 51 injects fuel in a state where the needle valve of the injector 51 does not reach the full-lift position. That is, in PL injection, the injector 51 injects fuel during the period from when the needle valve separates from the valve seat of the injector 51 until it seats on the valve seat again without reaching the full-lift position. The technical details of FL injection and PL injection are described in, for example, Japanese Unexamined Patent Application Publication No. 2016-223443.

[0021] <Injectable Range and Injection Prohibited Range> As shown in FIGS. 2 and 3, the control device 100 executes PL injection or FL injection based on injection permission information which is the range of the crank angle that defines whether fuel injection by the injector 51 is permitted. FIGS. 2 and 3 show the crank angle from the start timing M1 of the intake stroke to the end timing N2 of the compression stroke for a predetermined cylinder 11 by the angle of a clockwise circle. The crank angle of the start timing M1 of the intake stroke in the predetermined cylinder 11 is 0 degrees. The range defined by each timing such as the start timing M1 and the end timing N2 is a range that includes the timing of the timing itself that defines the range.

[0022] The injection feasibility information includes a first injection range X and a second injection range Y. The first injection range X and the second injection range Y are the ranges of crank angles in which fuel injection from the injector 51 is permitted. In the following, when describing the timing and range of fuel injection from the injector 51, unless otherwise specified, the timing and range will be described in terms of crank angle.

[0023] The first injection range X is predetermined within the range of crank angles from the start time M1 to the end time M2 of the intake stroke. The start time M1 of the intake stroke is the timing when the piston 12 is at top dead center. The end time M2 of the intake stroke is the timing when the piston 12 is at bottom dead center. The start time X1 of the first injection range X is retarded compared to the start time M1 of the intake stroke, and advanced compared to the crank angle of the midpoint MV of the intake stroke. Advancement is the crank angle being reversed relative to a predetermined crank angle, and retardation is the opposite. The start time X1 of the first injection range X is set to a limit crank angle at which the amount of fuel injected from the injector 51 that adheres to the top surface 12A of the piston 12 is less than or equal to a first allowable value. The first allowable value is defined, for example, as a value that can suppress the amount of particulate matter generated to a predetermined amount or less. The start time X1 of the first injection range X is, for example, a crank angle of approximately 60 degrees.

[0024] The final timing X2 of the first injection range X is retarded compared to the crank angle of the midpoint MV of the intake stroke, and advanced compared to the end timing M2 of the intake stroke. The final timing X2 of the first injection range X is set to a limit crank angle at which the amount of fuel injected from the injector 51 that adheres to the wall surface 11A of the cylinder 11 is less than or equal to a second allowable value. The second allowable value is defined, for example, as a value that can suppress the amount of unburned hydrocarbons emitted from the cylinder 11 to a predetermined amount or less. The final timing X2 of the first injection range X is, for example, a crank angle of approximately 120 degrees.

[0025] The second injection range Y is predetermined within the range of crank angles from the start time N1 to the end time N2 of the compression stroke. The second injection range Y is not continuous with the first injection range X. The second injection range Y is narrower than the first injection range X. The start time N1 of the compression stroke is when the piston 12 is at bottom dead center. The end time N2 of the compression stroke is when the piston 12 is at top dead center.

[0026] The starting time Y1 of the second injection range Y is retarded compared to the crank angle at the start time N1 of the compression stroke, and advanced compared to the crank angle at the center NV of the compression stroke. The starting time Y1 of the second injection range Y is set to the limit crank angle at which the amount of fuel injected from the injector 51 that adheres to the wall surface 11A of the cylinder 11 is less than or equal to the second allowable value. For example, the starting time Y1 of the second injection range Y is a crank angle of approximately 220 degrees. With respect to the end time M2 of the intake stroke, the starting time Y1 of the second injection range Y is set asymmetrically with respect to the end time X2 of the first injection range X. Specifically, the starting time Y1 of the second injection range Y is closer to the end time M2 of the intake stroke than to the end time X2 of the first injection range X.

[0027] The final stage Y2 of the second injection range Y is advanced compared to the crank angle at the center NV of the compression stroke. The final stage Y2 of the second injection range Y is set to a limit crank angle at which the amount of fuel injected from the injector 51 that adheres to the top surface 12A of the piston 12 is less than or equal to a first allowable value. The final stage Y2 of the second injection range Y is, for example, a crank angle of approximately 260 degrees. With respect to the end of the intake stroke M2, the final stage Y2 of the second injection range Y is set asymmetrically with respect to the start of the first injection range X X1. Specifically, the final stage Y2 of the second injection range Y is closer to the end of the intake stroke M2 than to the start of the first injection range X X X2.

[0028] The range of crank angles from the start of the intake stroke M1 to the start of the first injection range X X1 is defined as the first predetermined range P. The range of crank angles from the end of the first injection range X X2 to the start of the next second injection range Y Y1 is defined as the second predetermined range Q. The range of crank angles from the end of the second injection range Y Y2 to the end of the compression stroke N2 is defined as the third predetermined range R. These three predetermined ranges P, Q, and R are the ranges of crank angles in which fuel injection by the injector 51 is prohibited.

[0029] In the first predetermined range P and the third predetermined range R, the distance from the injection port 52 of the injector 51 to the top surface 12A of the piston 12 is short. Therefore, if fuel is injected in the first predetermined range P and the third predetermined range R, fuel is likely to adhere to the top surface 12A. For this reason, fuel injection is prohibited in the first predetermined range P and the third predetermined range R.

[0030] In the second predetermined range Q, the area of ​​the cylinder wall 11A, which is located above the top surface 12A of the piston 12, is large. Therefore, if fuel injection is performed in the second predetermined range Q, fuel is likely to adhere to the wall 11A. For this reason, fuel injection is prohibited in the second predetermined range Q.

[0031] <Injection control> Referring to Figures 4 and 5, the sequence of processes in injection control will be explained. Once the internal combustion engine 10 has finished starting, the control device 100 repeatedly performs injection control on the injector 51 until the ignition switch is turned off. Hereinafter, a certain period during the operation of the internal combustion engine 10 will be referred to as the control period. The control period is longer than the time required for one combustion cycle when the internal combustion engine 10 is operating at the minimum engine speed.

[0032] As shown in Figure 4, when the control device 100 starts injection control, it executes step S11. In step S11, the control device 100 calculates the total injection amount required for one cylinder 11 in one cycle of the internal combustion engine 10. The total injection amount is calculated based on parameters related to the operating state of the internal combustion engine 10. Once the control device 100 has calculated the total injection amount, it proceeds to step S12.

[0033] In step S12, the control device 100 sets the maximum number of injections based on, for example, the operating state of the internal combustion engine 10. The maximum number of injections is the maximum number of injections that can be performed by injecting fuel into one injector 51 in one combustion cycle of the internal combustion engine 10. As a prerequisite for the control device 100 to perform step S12, the control device 100 performs PL injection multiple times in one combustion cycle of the internal combustion engine 10. In this embodiment, since PL injection is performed at least once in each of the intake stroke and compression stroke, the maximum number of injections is two or more. The maximum number of injections is predetermined by experiment based on the total injection amount, the minimum fuel amount by PL injection, and the engine rotation speed. Information on the total injection amount, the minimum fuel amount by PL injection, and the engine rotation speed in relation to the maximum number of injections is stored in advance. The control device 100 calculates the engine rotation speed based on the change in crank angle received from the crank angle sensor 61. The control device 100 compares the total injection amount calculated in step S11, the minimum fuel amount for PL injection stored in advance, and the engine rotation speed calculated from the measured value of the crank angle sensor 61 with the information stored in advance to set the maximum number of injections. After setting the maximum number of injections, the control device 100 proceeds to step S13.

[0034] In step S13, the control device 100 distributes the maximum number of injections between the number of injections in the first injection range X of the intake stroke and the number of injections in the second injection range Y of the compression stroke. Hereinafter, the number of injections distributed to the first injection range X will be referred to as the first injection count, and the number of injections distributed to the second injection range Y will be referred to as the second injection count. If the maximum number of injections is even, the control device 100 makes the first injection count and the second injection count the same. If the maximum number of injections is odd, the control device 100 makes the first injection count one more than the second injection count, and makes the sum of the first injection count and the second injection count equal the maximum number of injections. After the distribution of the maximum number of injections is completed, the control device 100 proceeds to step S14.

[0035] In step S14, the control device 100 determines whether the amount of variation in the output torque of the internal combustion engine 10 is greater than or equal to a predetermined torque value. When the internal combustion engine 10 performs multiple fuel injections in one combustion cycle, the amount of fuel injected each time decreases, causing the amount of fuel injected from the injector 51 to vary, and thus increasing the variation in output torque between cylinders 11. This increased variation in output torque between cylinders 11 leads to a larger variation in the output torque of the internal combustion engine 10. The control device 100 determines the worsening of the variation in the amount of fuel injected from the injector 51 based on the amount of variation in the output torque of the internal combustion engine 10.

[0036] The output torque of cylinder 11 is the crank output torque corresponding to the combustion of the air-fuel mixture in a given cylinder 11. The control device 100 calculates the crank output torque from the derivative of the engine rotational speed. The larger the derivative of the engine rotational speed, the greater the output torque. The control device 100 monitors fluctuations in the output torque of the internal combustion engine 10 by monitoring the crank output torque of each cylinder 11. If the amount of fluctuation in the output torque of the internal combustion engine 10 is smaller than a predetermined torque value, the control device 100 proceeds to step S15.

[0037] In step S15, the control device 100 performs a first injection process. In the first injection process, the control device 100 injects a fuel injection amount corresponding to the first injection count within the first injection range X. The first injection process includes a process to calculate the injection start timing, injection interval, and injection amount so that the fuel injection amount corresponding to the first injection count can be completed within the first injection range X. Based on the calculated injection start timing, injection interval, and injection amount, the control device 100 performs fuel injection within the first injection range X. After performing the first injection process, the control device 100 proceeds to step S16.

[0038] In step S16, the control device 100 performs a second injection process. In the second injection process, the control device 100 injects a fuel injection amount corresponding to the second injection count within the second injection range Y. The second injection process includes a process to calculate the injection start timing, injection interval, and injection amount so that the fuel injection amount corresponding to the second injection count can be completed within the second injection range Y. Based on the calculated injection start timing, injection interval, and injection amount, the control device 100 performs fuel injection within the second injection range Y. After performing the second injection process, the control device 100 terminates its processing.

[0039] In step S14, if the fluctuation amount of the output torque of the internal combustion engine 10 is greater than or equal to a predetermined torque value, the control device 100 proceeds to step S17 in Figure 5. In step S17, the control device 100 determines whether FL injection is possible at least once. As a prerequisite for the control device 100 to perform step S13, the control device 100 performs FL injection at least once out of multiple injections when the fluctuation amount of the output torque of the internal combustion engine 10 is greater than or equal to a predetermined torque value. The control device 100 calculates the provisional total injection amount by assuming that one FL injection is performed in the maximum number of injections set in step S12, and PL injections are performed in the remaining number of injections after deducting one FL injection from the maximum number of injections. The injection amount of FL injection when calculating the provisional total injection amount is the minimum amount of fuel that can be injected with FL injection. The injection amount of PL injection when calculating the provisional total injection amount is the minimum amount of fuel that can be injected with PL injection. The control device 100 compares the total injection amount calculated in step S11 with the provisional total injection amount and determines that at least one FL injection is possible if the provisional total injection amount is less than or equal to the total injection amount. If at least one FL injection is possible, the control device 100 proceeds to step S18.

[0040] In step S18, the control device 100 determines whether the load on the internal combustion engine 10 is less than a predetermined load value. The control device 100 determines that the load on the internal combustion engine 10 is less than a predetermined load value if the engine load ratio is less than the load ratio for a predetermined period. The engine load ratio is a parameter that determines the amount of air filled into the cylinder 11. The control device 100 calculates the engine load ratio based on the engine rotational speed and the amount of intake air received from the air flow meter 62. The engine load ratio is the value obtained by dividing the amount of air flowing into one cylinder 11 per cycle of the internal combustion engine 10 by the reference air amount. The reference air amount changes according to the engine rotational speed. If the control device 100 determines that the load on the internal combustion engine 10 is less than a predetermined load value, it proceeds to step S19.

[0041] In step S19, the control device 100 applies the first injection rule. As a prerequisite for the control device 100 to execute step S19, the control device 100 performs multiple injections during the intake stroke of the internal combustion engine 10. The first injection rule is applied when the amount of fluctuation in the output torque of the internal combustion engine 10 is greater than or equal to a predetermined torque value, and the load on the internal combustion engine 10 is less than a predetermined load value. After applying the first injection rule, the control device 100 proceeds to step S15. When the first injection rule is applied, in step S15, the control device 100 performs the first injection during the intake stroke as an FL injection, and the second injection as a PL injection.

[0042] If the control device 100 determines in step S18 that the load on the internal combustion engine 10 is equal to or greater than a predetermined load value, it proceeds to step S20. In step S20, the control device 100 applies the second injection rule. As a prerequisite for the control device 100 to execute step S20, the control device 100 performs multiple injections during the intake stroke of the internal combustion engine 10. The second injection rule is applied when the amount of fluctuation in the output torque of the internal combustion engine 10 is equal to or greater than a predetermined torque value, and the load on the internal combustion engine 10 is equal to or greater than a predetermined load value. After applying the second injection rule, the control device 100 proceeds to step S15. When the second injection rule is applied, in step S15, the control device 100 performs the first injection during the intake stroke as a PL injection, and the second injection as an FL injection.

[0043] If, in step S17, the control device 100 determines that at least one FL injection is not possible, it proceeds to step S21. The control device 100 compares the total injection amount calculated in step S11 with the provisional total injection amount, and determines that at least one FL injection is not possible if the provisional total injection amount is greater than the total injection amount. In step S21, the control device 100 reduces the number of injections by one. After reducing the number of injections by one, the control device 100 proceeds to step S22. If the number of injections is already two before reducing the number of injections, the control device 100 proceeds from step S17 to step S25.

[0044] In step S22, the control device 100 determines whether the number of injections is 2 or not. If the number of injections is 3 or more, the control device 100 proceeds to step S23.

[0045] In step S23, the control device 100 determines whether FL injection is possible. The control device 100 determines that FL injection is possible if, by reducing the number of injections by one in step S21, one FL injection of the minimum injection amount can be performed and at least one PL injection of the minimum injection amount can be performed. If FL injection is possible, the control device 100 proceeds to step S18. If FL injection is not possible, the control device 100 repeats the process from step S21. The control device 100 determines that FL injection is not possible if, even after reducing the number of injections by one in step S21, one FL injection of the minimum injection amount cannot be performed.

[0046] If the number of injections in step S22 is 2, the control device 100 proceeds to step S24. In step S24, the control device 100 determines whether FL injection is possible. The control device 100 determines that FL injection is possible if reducing the number of injections by 1 in step S21 allows for one minimum injection of FL and one minimum injection of PL. If FL injection is possible, the control device 100 proceeds to step S15. If FL injection is not possible, the control device 100 proceeds to step S25. The control device 100 determines that FL injection is not possible if reducing the number of injections by 1 in step S21 does not allow for one minimum injection of FL and one minimum injection of PL.

[0047] In step S25, the control device 100 performs a low fuel pressure treatment. This treatment is performed by lowering the fuel supply pressure of the fuel pump 16 that supplies fuel to the injector 51. Assuming that the control device 100 performs the treatment in step S25, if it does not perform the low fuel pressure treatment, the control device 100 performs injection control at a common fuel pressure of a predetermined fuel pressure or higher. The low fuel pressure treatment is a process that reduces the fuel pressure to a level lower than the predetermined fuel pressure and lengthens the injection time. By lengthening the injection time, the needle valve of the injector 51 is more likely to reach the maximum lift position after leaving the valve seat, thus increasing the likelihood of performing FL injection. After performing the low fuel pressure treatment, the control device 100 proceeds to step S26.

[0048] In step S26, the control device 100 determines whether FL injection is possible. If FL injection is possible by extending the injection time through low fuel pressure processing, the control device 100 proceeds to step S15. As a result, FL injection is performed only once in the first injection range X, and PL injection is performed only once in the second injection range Y. If FL injection is not possible even after extending the injection time through low fuel pressure processing, the control device 100 proceeds to step S27. In step S27, the control device 100 performs either PL injection or FL injection once in the first injection range X, injecting an amount of fuel equal to the injection amount, and then terminates the process.

[0049] <Operation of the Embodiment> For example, suppose the control device 100 is performing injection control, and the maximum number of injections set by the control device 100 in step S12 is 5. Furthermore, suppose that when the amount of fluctuation in the output torque of the internal combustion engine 10 is greater than or equal to a predetermined torque value, at least one FL injection is possible, and the load on the internal combustion engine 10 is less than a predetermined load value. In this case, as shown in Figure 2, the control device 100 in step S13 distributes the number of injections in the intake stroke to 3 and the number of injections in the compression stroke to 2. Then, in step S15, the control device 100 performs the first injection of the intake stroke as an FL injection and the second injection as a PL injection, in accordance with the first injection rule applied in step S19.

[0050] Similarly, assume that the control device 100 is performing injection control, and that the maximum number of injections set by the control device 100 in step S12 is 5. Furthermore, assume that at least one FL injection is possible when the amount of fluctuation in the output torque of the internal combustion engine 10 is greater than or equal to a predetermined torque value, and that the load on the internal combustion engine 10 is greater than or equal to a predetermined load value. In this case, as shown in Figure 3, the control device 100 in step S13 distributes the number of injections in the intake stroke to 3 and the number of injections in the compression stroke to 2. Then, in step S15, the control device 100 performs the first injection of the intake stroke as a PL injection and the second injection as an FL injection, in accordance with the second injection rule applied in step S20. Note that Figures 2 and 3 are explanatory diagrams to clearly illustrate the characteristics of each injection pattern and do not necessarily reflect the actual injection amount or injection interval.

[0051] <Effects of the Embodiment> (1) The fuel injection system 50 includes an injector 51 provided for each of the multiple cylinders 11 of the internal combustion engine 10 to inject fuel into the cylinder 11, and a control device 100 that controls the fuel injection by the injector 51. The control device 100 performs PL injection multiple times in one combustion cycle, in which fuel is injected when the needle valve of the injector 51 has not reached the FL position. When the amount of fluctuation in the output torque of the internal combustion engine 10 is greater than or equal to a predetermined torque value, the control device 100 performs FL injection at least once out of the multiple fuel injections, in which fuel is injected when the needle valve of the injector 51 has reached the FL position.

[0052] FL injection exhibits less variation in the injection amount per injection compared to PL injection. Therefore, compared to the case where all fuel injections are PL injections, the variation in the injection amount for each cylinder 11 is smaller when at least one FL injection is performed. As a result, the fluctuation in the output torque of the internal combustion engine 10 is less likely to become large.

[0053] (2) The control device 100 performs FL injection during the intake stroke of the internal combustion engine 10. When FL injection is performed during the intake stroke, the time until the injected fuel is ignited is longer compared to when FL injection is performed during the compression stroke. As a result, the fuel vaporizes more easily, and the fuel and intake air mix more uniformly.

[0054] (3) The control device 100 performs multiple fuel injections during the intake stroke of the internal combustion engine 10. The control device 100 performs the first fuel injection during the intake stroke as an FL injection, and the second fuel injection as a PL injection.

[0055] Compared to PL injection, FL injection injects a larger amount of fuel in a single burst. Therefore, when the first fuel injection during the intake stroke is performed using FL injection, more fuel tends to mix uniformly with the intake air compared to when the first fuel injection during the intake stroke is performed using PL injection.

[0056] (4) The control device 100 performs multiple fuel injections during the intake stroke of the internal combustion engine 10. When the fluctuation amount of the output torque of the internal combustion engine 10 is greater than or equal to a predetermined torque value and the load of the internal combustion engine 10 is less than a predetermined load value, the control device 100 performs the first fuel injection during the intake stroke as an FL injection and the second fuel injection as a PL injection. When the fluctuation amount of the output torque of the internal combustion engine 10 is greater than or equal to a predetermined torque value and the load of the internal combustion engine 10 is greater than or equal to a predetermined load value, the control device 100 performs the first fuel injection during the intake stroke as a PL injection and the second fuel injection as an FL injection.

[0057] When the load on the internal combustion engine 10 is less than a predetermined load value, the amount of fuel injected by FL injection is less compared to when the load on the internal combustion engine 10 is equal to or greater than the predetermined load value. Therefore, when the load on the internal combustion engine 10 is less than a predetermined load value, even if the first fuel injection during the intake stroke is performed by FL injection, fuel is less likely to adhere to the top surface 12A of the piston 12 of the internal combustion engine 10. In addition, when the first fuel injection during the intake stroke is performed by FL injection, the time until the injected fuel ignites is longer compared to when the second fuel injection during the intake stroke is performed by FL injection, so the fuel is more likely to vaporize.

[0058] The distance from the injection port 52 of the injector 51 to the top surface 12A of the piston 12 is longer when the second fuel injection is performed during the intake stroke compared to when the first fuel injection is performed during the intake stroke. Therefore, when the load of the internal combustion engine 10 is above a predetermined load value, the second injection during the intake stroke is performed as a full-line injection. As a result, less fuel adheres to the top surface 12A of the piston 12 than when the first fuel injection during the intake stroke is performed as a full-line injection. Consequently, the fuel and intake air mix more uniformly.

[0059] <Example of changes> The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0060] The fuel injection amount and injection start timing for each injection when the injector 51 performs fuel injection in the first injection process can be changed as appropriate. As shown in Figures 2 and 3, it is not necessary for the start timing of the first fuel injection in the first injection process to be the start time X1 of the first injection range X.

[0061] • When injecting fuel into the injector 51 during the second injection process, the fuel injection amount and injection start timing for each injection can be changed as appropriate. As shown in Figures 2 and 3, it is not necessary for the end timing of the last fuel injection in the second injection process to be the end time Y2 of the second injection range Y.

[0062] The control device 100 may perform at least one FL injection during the compression stroke instead of performing at least one FL injection during the intake stroke. The control device 100 may, in step S26, perform one PL injection in the second injection range Y instead of performing one PL injection in the first injection range X.

[0063] The control device 100 may omit steps S18 and S20 and proceed with the process. That is, if multiple injections are performed during the intake stroke of the internal combustion engine 10, the first injection in the first injection range X may be an FL injection regardless of the load of the internal combustion engine 10.

[0064] The control device 100 may skip steps S18 to S20 and proceed with the processing. That is, if multiple injections are performed during the intake stroke of the internal combustion engine 10, the control device 100 may perform an FL injection at any timing within the first injection range X, regardless of the load on the internal combustion engine 10, as long as at least one FL injection is performed. [Explanation of Symbols]

[0065] 10...Internal combustion engine, 11...Cylinder, 50...Fuel injection system, 51...Injector, 100...Control device.

Claims

1. A fuel injection system comprising: an injector provided for each of the multiple cylinders of an internal combustion engine for injecting fuel into the cylinder; and a control device for controlling the fuel injection by the injector, The control device is In a single combustion cycle, partial lift injection is performed multiple times, in which fuel is injected while the needle valve of the injector has not reached the full lift position. When the amount of fluctuation in the output torque of the internal combustion engine is greater than or equal to a predetermined torque value, at least one of the multiple fuel injections shall be a full-lift injection, in which fuel is injected with the needle valve of the injector at the full-lift position. Fuel injection device.

2. The control device performs the full-lift injection during the intake stroke of the internal combustion engine. The fuel injection device according to claim 1.

3. The control device is Multiple fuel injections are performed during the intake stroke of the internal combustion engine. The first fuel injection during the intake stroke is performed using the full-lift injection method, and the second fuel injection is performed using the partial-lift injection method. The fuel injection device according to claim 2.

4. The control device is Multiple fuel injections are performed during the intake stroke of the internal combustion engine. When the amount of fluctuation is greater than or equal to a predetermined torque value, and the load on the internal combustion engine is less than a predetermined load value, the first fuel injection during the intake stroke is performed as a full-lift injection, and the second fuel injection is performed as a partial-lift injection. When the amount of fluctuation is equal to or greater than the predetermined torque value and the load is equal to or greater than the predetermined load value, the first fuel injection during the intake stroke is performed as a partial lift injection, and the second fuel injection is performed as a full lift injection. The fuel injection device according to claim 2.

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