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 device 50 includes an injector 51 and a control device 100 that controls the injection of fuel by the injector 51. The fuel injection device 50 performs intake stroke injection and compression stroke injection multiple times each. In at least one of the intake stroke injection and compression stroke injection, the first injection is set to have the shortest period between the injection timing of the first injection and the top dead center timing, and the second injection is set to have a longer period between the injection timing of the second injection and the top dead center timing than the first injection. The control device 100 then performs an injection ratio change process to change the first injection ratio and the second injection ratio so that the first injection ratio, which is the ratio of the injection amount of the first injection to the total injection amount, is greater than the second injection ratio, which is the ratio of the injection amount of the second injection to the total injection amount.

Description

Technical Field

[0004] , ,

[0005] , , ,

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

Background Art

[0002] The internal combustion engine disclosed in Patent Document 1 includes a control device that controls fuel injection. The control device executes multiple fuel injections in one combustion cycle of the internal combustion engine. The control device increases the fuel injection amount of the cylinder where output torque fluctuations occur based on the rotational fluctuation value.

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 fuel injection amount per injection decreases. When the fuel injection amount decreases, the injection amount per cylinder is likely to vary, so the output torque fluctuations of the internal combustion engine may increase. There is room for improvement in the method of changing various parameters in injection control to suppress variations in the fuel amount supplied to each cylinder.

Means for Solving the Problems

[0005] 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, wherein the system performs multiple intake stroke injections, which are fuel injections within the range from the start to the end of the intake stroke, and multiple compression stroke injections, which are fuel injections within the range from the start to the end of the compression stroke, wherein in at least one of the intake stroke injections and the compression stroke injections, the first injection is set to coincide with the injection timing of the first injection and the time when the piston in the cylinder is at top dead center. When the injection with the shortest interval between the two timings is set, and the second injection is set such that the interval between the injection timing of the second injection and the top dead center timing is longer than that of the first injection, the control device executes an injection ratio change process to change the first injection ratio and the second injection ratio so that the first injection ratio, which is the ratio of the injection amount of the first injection to the total injection amount (the sum of the injection amounts of the first and second injections), is greater than the second injection ratio, which is the ratio of the injection amount of the second injection to the total injection amount, when the amount of fluctuation of the output torque of the internal combustion engine is greater than a predetermined amount. [Effects of the Invention]

[0006] The fuel injection system of this disclosure can suppress fluctuations in output torque caused by variations in the amount of fuel injected from cylinder to cylinder. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram of an internal combustion engine having a fuel injection system according to the present disclosure. [Figure 2] Figure 1 is a schematic diagram illustrating the fuel injection timing by the fuel injection system. [Figure 3] This graph shows the relationship between the injection ratio, the amount of output torque fluctuation, the amount of particulate matter, and the amount of unburned fuel. [Figure 4] This graph shows the relationship between injection interval, output torque fluctuation, particulate matter amount, and unburned fuel amount. [Figure 5] This graph shows the relationship between the number of injections, the amount of output torque fluctuation, the amount of particulate matter, and the amount of unburned fuel. [Figure 6] Figure 1 is a flowchart showing the injection control process performed by the control device. [Modes for carrying out the invention]

[0008] <Overall Configuration of an Internal Combustion Engine> The internal combustion engine 10 of this disclosure will be described with reference to Figures 1 to 6. As shown in Figure 1, the vehicle is equipped with the 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 disclosure, there are four cylinders 11.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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 three-way catalytic converter 31 and a filter 32 are arranged in the exhaust passage 30 for purifying and collecting harmful substances contained in the exhaust gas. The three-way catalytic converter 31 is located in the middle of the exhaust passage 30. The three-way catalytic converter 31 purifies hydrocarbons, carbon monoxide, and nitrogen oxides contained in the exhaust gas. The filter 32 is located downstream of the three-way catalytic converter 31 in the exhaust passage 30. The filter 32 collects particulate matter contained in the exhaust gas.

[0013] 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 twice.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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 according to the detected information to the control device 100.

[0018] <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 perform full lift injection or partial lift injection. Hereinafter, partial lift is abbreviated as "PL" and full lift is abbreviated as "FL" for description.

[0019] 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 of the injector 51 when it 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.

[0021] The control device 100 executes multiple injections in the PL injection with the smallest injection amount. When increasing the injection amount of each injection according to the total amount of fuel injection, the fluctuation amount of the output torque, and the deterioration of emissions, the injection amount of the PL injection is gradually increased, and finally, at least one of the multiple injections is executed by FL injection.

[0022] <The First Injection Range and the Second Injection Range> In the present disclosure, when explaining the timing, period, range, etc. of fuel injection of the injector 51, it is explained as the timing, period, and range in terms of the crank angle. Also, the injection start timing and the injection end timing are described as the injection timing unless otherwise explicitly stated.

[0023] As shown in FIG. 2, the control device 100 executes multiple intake stroke injections that inject fuel during the intake stroke. The control device 100 executes multiple compression stroke injections that inject fuel during the compression stroke.

[0024] The start time M1 of the intake stroke is when the piston 12 is at top dead center (hereinafter referred to as the top dead center time). The end time M2 of the intake stroke is when the piston 12 is at bottom dead center (hereinafter referred to as the bottom dead center time). The start time N1 of the compression stroke is the bottom dead center time. The end time N2 of the compression stroke is the top dead center time.

[0025] The control device 100 performs fuel injection based on injection timing information, which is a range of crank angle that defines whether or not fuel injection by the injector 51 is appropriate. The injection timing information includes a first injection range X and a second injection range Y. The control device 100 prioritizes selecting the first injection range X as the injection timing for the intake stroke over other ranges of the intake stroke. The control device 100 prioritizes selecting the second injection range Y as the injection timing for the compression stroke over other ranges of the compression stroke.

[0026] <Start and end times of the first injection range X> The first injection range X is determined within the range of crank angles from the start time M1 to the end time M2 of the intake stroke. The start time X1 of the first injection range X is a time that is retarded compared to the start time M1 of the intake stroke. At the start time X1 of the first injection range X, a limit crank angle is set such that the amount of fuel injected from the injector 51 that adheres to the top surface 12A of the piston 12 (hereinafter referred to as the top surface adhesion amount) is less than or equal to a first allowable value. The first allowable value is determined, for example, as a value that can suppress the amount of particulate matter contained in the exhaust to a predetermined amount or less.

[0027] The end of the first injection range X, X2, is an advanced timing point compared to the end of the intake stroke, M2. At the end of the first injection range X, X2, a limit crank angle is set such that the amount of fuel injected from the injector 51 that adheres to the wall surface 11A of the cylinder 11 (hereinafter referred to as wall adhesion amount) is less than or equal to a second allowable value. The second allowable value is determined, for example, as a value that can keep the amount of unburned hydrocarbons (hereinafter referred to as unburned fuel) emitted from the cylinder 11 below a predetermined amount.

[0028] <Start Y1 and end Y2 of the second injection range Y> 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.

[0029] The start time Y1 of the second injection range Y is retarded compared to the crank angle at which the compression stroke starts N1. The start time Y1 of the second injection range Y is set to the limit crank angle at which the wall adhesion amount is less than or equal to the second allowable value.

[0030] The final stage Y2 of the second injection range Y is the time when the crank angle is advanced compared to the central NV of the compression stroke. The final stage Y2 of the second injection range Y is set to the limit crank angle at which the amount of top surface deposit is less than or equal to the first allowable value.

[0031] <First predetermined range P, second predetermined range Q, and third predetermined range R> 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.

[0032] 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, when fuel is injected in the first predetermined range P and the third predetermined range R, the amount of fuel adhering to the top surface tends to increase.

[0033] In the second predetermined range Q, the area of ​​the wall surface 11A of the cylinder 11, which is located above the top surface 12A of the piston 12 (hereinafter referred to as the exposed area), is large. Therefore, when fuel injection is performed in the second predetermined range Q, the amount of fuel adhering to the wall surface tends to increase.

[0034] The first injection range X is a range within the intake stroke in which emission deterioration is less likely to occur. The second injection range Y is a range within the compression stroke in which emission deterioration is less likely to occur. In the intake stroke, the first predetermined range P and the second predetermined range Q are ranges in which emission deterioration is more likely to occur compared to the first injection range X. In the compression stroke, the third predetermined range R is a range in which emission deterioration is more likely to occur compared to the first injection range X. An increase in unburned fuel and particulate matter in the exhaust is an example of emission deterioration.

[0035] <First intake stroke injection and second intake stroke injection> The control device 100 performs a first injection and a second injection during the intake stroke and the compression stroke, respectively. The first injection is the injection with the shortest period between the injection timing and the top dead center timing. The second injection is an injection in which the period between the injection timing and the top dead center timing is longer than that of the first injection.

[0036] The first injection includes the first intake stroke injection. The first intake stroke injection is the first injection performed during the intake stroke. The second injection includes the second intake stroke injection. For example, if the control device 100 performs intake stroke injections only three times, the second intake stroke injections are the second and third injections performed during the intake stroke, respectively. The period between the injection timing and top dead center timing of the second injection during the intake stroke is longer than the period between the injection timing and top dead center timing of the first intake stroke injection. The period between the injection timing and top dead center timing of the third injection during the intake stroke is longer than the period between the injection timing and top dead center timing of the first intake stroke injection and the period between the injection timing and top dead center timing of the second injection.

[0037] <First intake stroke injection ratio and second intake stroke injection ratio> The first injection ratio is the ratio of the injection amount of the first injection to the total injection amount, which is the sum of the injection amounts of the first and second injections. The first injection ratio includes the first intake stroke injection ratio. The first intake stroke injection ratio is the ratio of the injection amount of the first intake stroke injection to the total injection amount of the intake stroke injections.

[0038] The second injection ratio is the ratio of the injection amount of the second injection to the total injection amount, which is the sum of the injection amounts of the first and second injections. The second injection ratio includes the second intake stroke injection ratio. The second intake stroke injection ratio is the ratio of the injection amount of the second intake stroke injection to the total injection amount of the intake stroke injections.

[0039] Among multiple injections, injections with a larger injection volume have a greater impact on the variation in output torque compared to injections with a smaller injection volume, while the variation in injection volume is smaller. For example, comparing the case of performing two injections with equal injection volumes with the case of increasing the volume of one of the two injections and decreasing the volume of the other by the same amount, the variation in injection volume is smaller in the latter case. Therefore, if the ratios of the first and second injections are changed so that the ratio of the first injection is greater than the ratio of the second injection, the variation in injection volume will be reduced.

[0040] In intake stroke injection, the period during which the injected fuel and intake air are mixed is longer in the first intake stroke injection than in the second intake stroke injection. Therefore, the fuel injected in the first intake stroke injection is more easily mixed homogeneously with the intake air compared to the fuel injected in the second intake stroke injection. Consequently, by increasing the injection amount in the first intake stroke injection, which mixes more homogeneously with the intake air compared to the second intake stroke injection, emissions are less likely to deteriorate. However, if the injection amount in the first intake stroke injection is too high, the amount of fuel adhering to the top surface will increase, thus worsening emissions.

[0041] <First compression stroke injection and second compression stroke injection> The first injection includes the first compression stroke injection. For example, if the control device 100 performs only two compression stroke injections, the first compression stroke injection is the second injection performed during the compression stroke. The second injection includes the second compression stroke injection. The second compression stroke injection is the first injection performed during the compression stroke. The period between the second compression stroke injection and the top dead center timing is longer than the period between the first compression stroke injection and the top dead center timing.

[0042] <First Compression Stroke Injection Ratio and Second Compression Stroke Injection Ratio> The first injection ratio includes the first compression stroke injection ratio. The first compression stroke injection ratio is the ratio of the injection amount of the first compression stroke injection to the total injection amount of the compression stroke injection. The second injection ratio includes the second compression stroke injection ratio. The second compression stroke injection ratio is the ratio of the injection amount of the second compression stroke injection to the total injection amount of the compression stroke injection.

[0043] Compared to the second compression stroke injection, the first compression stroke injection results in a smaller exposed area and therefore less wall adhesion. Consequently, increasing the injection volume of the first compression stroke injection, which results in less wall adhesion compared to the second compression stroke injection, helps to prevent emissions from deteriorating. However, increasing the injection volume of the first compression stroke injection too much will increase top surface adhesion, thus worsening emissions.

[0044] <Changes in the first injection ratio and the second injection ratio> In this disclosure, when the injection amount of the first injection (Qin1) is increased by a predetermined value α and the injection amount of the second injection (Qin2) is decreased by a predetermined value α, the changes in the first injection ratio and the changes in the second injection ratio are defined, for example, by the following equations (1) and (2). The following equations (1) and (2) are examples of methods for defining the changes in the first injection ratio and the changes in the second injection ratio.

[0045] Change in the first injection ratio = |(Qin1+α) / (Qin1+Qin2)-(Qin1) / (Qin1+Qin2)|=α / (Qin1+Qin2)…(1) Change in the second injection ratio = |(Qin2-α) / (Qin1+Qin2)-(Qin2) / (Qin1+Qin2)|=α / (Qin1+Qin2)…(2) Since the sum of the injection amounts for the first and second injections remains constant even when the first and second injection ratios are changed, the amount of change in the first injection ratio and the amount of change in the second injection ratio, as defined by the above formula, are equal. Therefore, the amount of change in the first intake stroke injection ratio and the amount of change in the second intake stroke injection ratio are equal, and the amount of change in the first compression stroke injection ratio and the first compression stroke injection ratio are equal. For this reason, below, the amounts of change in the first intake stroke injection ratio and the second intake stroke injection ratio will both be described as the amount of change in the first intake stroke injection ratio, and the amounts of change in the first compression stroke injection ratio and the second compression stroke injection ratio will both be described as the amount of change in the first compression stroke injection ratio.

[0046] <Injection interval> The injection interval is the period between the injection timing of the first injection and the injection timing of the second injection. For example, in intake stroke injection, the injection interval is the period between the end of the first injection and the start of the second injection. If the control device 100 performs intake stroke injection only three times, the injection interval for intake stroke injection may be the period between the end of the first intake stroke injection and the start of the second intake stroke injection, or it may be the period between the end of the first intake stroke injection and the start of the second intake stroke injection. Furthermore, the injection interval for intake stroke injection may be the period between the end of the first intake stroke injection and the start of the third intake stroke injection. In intake stroke injection, the injection interval is lengthened by retarding the injection timing of the second intake stroke injection.

[0047] For example, the injection interval in compression stroke injection is the period between the end of the second injection and the start of the first injection. If the control device 100 performs compression stroke injection only twice, the injection interval for compression stroke injection may be the period between the end of the second compression stroke injection and the start of the first compression stroke injection. In compression stroke injection, the injection interval is lengthened by advancing the injection timing of the second compression stroke injection.

[0048] Injector 51 opens when the needle valve is pulled up by the electromagnetic force of an electromagnet. When the current to the electromagnet is cut off, the needle valve is lowered by the force of a spring, closing the valve. Immediately after injector 51 closes, the components inside injector 51 vibrate. If injector 51 is opened while these components are vibrating, the amount of fuel injected will vary.

[0049] Therefore, by lengthening the injection interval, the injector 51 opens after the vibration of the injector components has subsided. As a result, variations in the injection amount are reduced. However, lengthening the injection interval reduces the number of injections during the intake stroke and compression stroke, making it more difficult for the fuel to vaporize. Also, lengthening the injection interval means that the second injection is performed when the exposed area is large, increasing the amount of fuel adhering to the wall. As a result, emissions tend to worsen.

[0050] <Injection ratio, injection interval, and number of injections> The solid lines, dashed lines, and dashed lines in Figures 3 to 5 represent the fluctuation in output torque, the amount of particulate matter, and the amount of unburned fuel, respectively. The relationships between the fluctuation in output torque of the internal combustion engine 10, the amount of particulate matter in the exhaust, and the amount of unburned fuel in the exhaust, for each of the injection ratio, injection interval, and number of injections shown in Figures 3 to 5, can be determined experimentally.

[0051] As shown in Figure 3, the amount of output torque variation decreases across the entire range of the injection ratio as the injection ratio increases. Both the amount of particulate matter and the amount of unburned fuel increase across the entire range of the injection ratio as the injection ratio increases.

[0052] When the first intake stroke injection ratio and the first compression stroke injection ratio increase, the amount of fuel injected in the first intake stroke and first compression stroke increases, resulting in a larger amount of fuel adhering to the top surface. As a result, the amount of particulate matter and unburned fuel increases.

[0053] As shown in Figure 4, the amount of fluctuation in output torque decreases as the injection interval increases, except in the range of extremely short injection intervals, and the degree of decrease is smaller than the degree of decrease when the injection ratio is increased. The amount of particulate matter and unburned fuel increases as the injection interval increases, and the degree of increase is larger than the degree of increase when the injection ratio is increased.

[0054] In this embodiment, during intake stroke injection, the injection interval is changed by changing the injection timing of the second intake stroke injection without changing the injection timing of the first intake stroke injection. Similarly, during compression stroke injection, the injection interval is changed by changing the injection timing of the second compression stroke injection without changing the injection timing of the first compression stroke injection. Therefore, increasing the injection interval shortens the period between the injection timing and bottom dead center timing of the second intake stroke injection and the second compression stroke injection, resulting in a larger exposed area and an increase in wall adhesion. As a result, the amount of particulate matter and unburned fuel increases.

[0055] As shown in Figure 5, the amount of fluctuation in output torque decreases as the number of injections decreases, except in the range where the number of injections is extremely high. The degree of decrease is smaller than the degree of decrease when the injection ratio is increased, and is about the same as or slightly smaller than the degree of decrease when the injection interval is lengthened. The amount of particulate matter and unburned fuel increases as the number of injections decreases. The degree of increase is larger than the degree of increase when the injection ratio is increased, and is about the same as or slightly smaller than the degree of decrease when the injection interval is shortened.

[0056] The experimental results shown in Figures 3 to 5 indicate that, in order of effectiveness, increasing the injection ratio, extending the injection interval, and reducing the number of injections are effective in reducing fluctuations in output torque while suppressing the deterioration of emissions.

[0057] <Injection control> Referring to Figure 6, 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.

[0058] As shown in Figure 6, 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.

[0059] In step S12, the control device 100 sets the maximum number of injections based on the operating state of the internal combustion engine 10. The maximum number of injections is the maximum number of injections that can be performed on one injector 51 in one combustion cycle of the internal combustion engine 10. The maximum number of injections is predetermined by experiment based on the total injection amount, the minimum fuel amount due to PL injection, and the engine rotation speed. The control device 100 stores the information on the total injection amount, the minimum fuel amount due to PL injection, and the engine rotation speed 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 sets the maximum number of injections by comparing the total injection amount calculated in step S11, the minimum fuel amount due to 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. After setting the maximum number of injections, the control device 100 proceeds to step S13.

[0060] In step S13, the control device 100 distributes the maximum number of injections between the number of intake stroke injections in the first injection range X and the number of compression stroke injections in the second injection range Y. Hereinafter, the number of intake stroke injections in the first injection range X will be referred to as the first number, and the number of compression stroke injections in the second injection range Y will be referred to as the second number. If the maximum number of injections is even, the control device 100 makes the first number and the second number the same. If the maximum number of injections is odd, the control device 100 makes the first number one more than the second number, and makes the sum of the first number and the second number equal to the maximum number of injections. After the distribution of the maximum number of injections is completed, the control device 100 proceeds to step S14.

[0061] In step S14, the control device 100 sets the injection timing. The control device 100 sets the injection timing for the intake stroke injection by calculating the injection start time, injection interval, and injection amount so that the intake stroke injection can be completed within the first injection range X. The control device 100 sets the injection timing for the compression stroke injection by calculating the injection start time, injection interval, and injection amount so that the compression stroke injection can be completed within the second injection range Y. After setting the injection timing, the control device 100 proceeds to step S15.

[0062] In step S15, the control device 100 calculates the torque difference ΔT. The torque difference ΔT is the value obtained by subtracting the average value of the output torque of all cylinders 11 from the average value of the output torque of a predetermined cylinder 11 over the control period. The output torque of a cylinder 11 is the crank output torque corresponding to the combustion of the air-fuel mixture in the predetermined cylinder 11. The control device 100 calculates the crank output torque from the derivative of the engine rotation speed. The larger the derivative of the engine rotation speed, the larger the output torque. The control device 100 monitors the amount of fluctuation in the output torque of the internal combustion engine 10 by monitoring the crank output torque of each cylinder 11. After calculating the torque difference ΔT for each cylinder 11, the control device 100 proceeds to step S16.

[0063] In step S16, the control device 100 determines whether the fluctuation amount of the output torque of the internal combustion engine 10 is greater than or equal to a predetermined fluctuation amount. The control device 100 determines the deterioration of the variation in the amount of fuel injected from the injector 51 based on the fluctuation amount of the output torque of the internal combustion engine 10. For example, if there is a cylinder 11 in which the absolute value of the torque difference ΔT calculated in step S15 is greater than a predetermined threshold, the control device 100 determines that the fluctuation amount of the output torque is greater than or equal to a predetermined fluctuation amount. The predetermined fluctuation amounts in steps S16, S21, and S24 may all be the same, any two of them may be the same, or all three may be different. If the fluctuation amount of the output torque is less than the predetermined fluctuation amount, the control device 100 proceeds to step S17.

[0064] In step S17, the control device 100 performs a first injection process. In the first injection process, the control device 100 performs intake stroke injection within the first injection range X. After performing the first injection process, the control device 100 proceeds to step S18.

[0065] In step S18, the control device 100 performs a second injection process. In the second injection process, the control device 100 performs a compression stroke injection within the second injection range Y. After performing the second injection process, the control device 100 terminates the process.

[0066] <Injection ratio change process> In step S16, if the amount of fluctuation in the output torque of the internal combustion engine 10 is greater than or equal to a predetermined amount, the control device 100 proceeds to step S20. In step S20, the control device 100 executes an injection ratio change process. The control device 100 changes the first intake stroke injection ratio so that the first intake stroke injection ratio increases by a predetermined amount. Therefore, as 100 repeatedly executes the process in step S20, the amount of change in the first intake stroke injection ratio gradually increases. The control device 100 changes the second compression stroke injection ratio so that the first compression stroke injection ratio increases by a predetermined amount. Therefore, as 100 repeatedly executes the process in step S20, the amount of change in the first compression stroke injection ratio gradually increases. After executing the injection ratio change process, the control device 100 proceeds to step S21.

[0067] In step S21, the control device 100 determines whether the amount of fluctuation in the output torque of the internal combustion engine 10 is greater than or equal to a predetermined amount of fluctuation. In step S21, the control device 100 makes a determination based on the same criteria as in step S16. If the amount of fluctuation in the output torque is less than the predetermined amount of fluctuation, the control device 100 proceeds to step S17. If the amount of fluctuation in the output torque is greater than or equal to the predetermined amount of fluctuation, the control device 100 proceeds to step S22.

[0068] After performing the injection ratio change process, in step S22, the control device 100 determines whether the amount of change in the first intake stroke injection ratio and the amount of change in the first compression stroke injection ratio have reached a first threshold determined separately for each. The first threshold determined for the amount of change in the first intake stroke injection ratio may be the same as or different from the first threshold determined for the amount of change in the first compression stroke injection ratio. In step S22, the control device 100 may, for example, make a positive determination if both the amount of change in the first intake stroke injection ratio and the amount of change in the first compression stroke injection ratio have reached the first threshold, or it may make a positive determination if at least one of the amount of change in the first intake stroke injection ratio and the amount of change in the first compression stroke injection ratio has reached the first threshold.

[0069] The first threshold values ​​for the first intake stroke injection ratio and the first compression stroke injection ratio are determined, for example, in relation to unburned fuel in the exhaust. The first threshold is set as a value that reaches the maximum allowable amount of particulate matter and unburned fuel in the exhaust. The maximum allowable amount is set as a value that allows for a deterioration in drivability.

[0070] If the control device 100 determines that the condition is negative in step S22, it proceeds to step S16. If the control device 100 determines that the condition is positive in step S22, it proceeds to step S23. After determining that the condition is positive in step S22, the control device 100 does not change the first intake stroke injection ratio or the first compression stroke injection ratio.

[0071] <Injection interval change process> In step S23, the control device 100 performs an injection interval modification process. This process extends the injection intervals for intake stroke injection and compression stroke injection. The following describes the case where the control device 100 performs intake stroke injection only three times and compression stroke injection only twice.

[0072] For example, the control device 100 extends the injection interval in the intake stroke by retarding the injection timing of the second intake stroke injection and the injection timing of the third intake stroke injection. For example, the control device 100 may extend the injection interval by retarding only the injection timing of the second intake stroke injection, or by retarding only the injection timing of the third intake stroke injection.

[0073] For example, the control device 100 extends the injection interval in the compression stroke injection by advancing the injection timing of the first compression stroke injection. The control device 100 gradually increases the amount of change in the injection interval of the intake stroke injection and the amount of change in the injection interval of the compression stroke injection. Next, the control device 100 proceeds to step S24.

[0074] Next, in step S24, the control device 100 determines whether the amount of fluctuation in the output torque of the internal combustion engine 10 is greater than or equal to a predetermined amount of fluctuation. In step S24, the control device 100 makes a determination based on the same criteria as in steps S16 and S20. If the amount of fluctuation in the output torque is less than the predetermined amount of fluctuation, the control device 100 proceeds to step S17. If the amount of fluctuation in the output torque is greater than or equal to the predetermined amount of fluctuation, the control device 100 proceeds to step S25.

[0075] In step S25, the control device 100 determines whether the amount of change in the injection interval for the intake stroke injection and the amount of change in the injection interval for the compression stroke injection have reached a second threshold determined for each. This second threshold may be the same as or different from the second threshold determined for the amount of change in the injection interval for the intake stroke injection. In step S25, the control device 100 may, for example, make a positive determination if both the amount of change in the injection interval for the first intake stroke injection and the amount of change in the injection interval for the first compression stroke injection have reached the first threshold, or it may make a positive determination if at least one of the amount of change in the first intake stroke injection ratio and the amount of change in the first compression stroke injection ratio has reached the first threshold.

[0076] The second threshold is set, for example, based on the injectable range. The second threshold is set, for example, as a value that reaches the maximum allowable amount of particulate matter and unburned fuel contained in the exhaust. The maximum allowable amount is set as a value that allows for a deterioration in drivability. If the control device 100 makes a negative determination in step S25, it proceeds to step S16. If the control device 100 makes a positive determination in step S25, it proceeds to step S26. After making a positive determination in step S25, the control device 100 does not change the injection interval of the first intake stroke injection or the injection interval of the first compression stroke injection.

[0077] <Processing to change the number of injections> In step S26, the control device 100 performs an injection count modification process. When the control device 100 performs the process in step S26 for the first time, it reduces the total injection count calculated in step S11 by 1. Each time the control device 100 performs the process in step S26, it reduces the injection count by 1 from the previous injection count. The control device 100 may also stop the second injection first, out of the first and second injections.

[0078] For example, the control device 100 reduces the number of injections by stopping the injections from the injector 51 in the following order: second compression stroke injection, third intake stroke injection, second intake stroke injection, and first compression stroke injection. The process then proceeds to step S16. In this case, at least one of the change in the first intake stroke injection ratio and the change in the first compression stroke injection ratio has reached a first threshold.

[0079] Furthermore, at least one of the change in the injection interval for the intake stroke injection and the injection interval for the compression stroke injection has reached the second threshold. For this reason, the control device 100 skips the processing from steps S20 to S25 and executes the processing in step S26. Also, if the number of injections becomes 1 after executing the injection count change processing, the process proceeds to step S17. The control device 100 executes one intake stroke injection.

[0080] <Effects of this disclosure> (1) By performing the injection ratio modification process, variations in injection volume are reduced, and the amount of fluctuation in output torque is reduced. As the injection volume of the first intake stroke increases, the amount of fuel that is homogeneously mixed with the intake air increases. As the injection volume of the first compression stroke increases, the amount of fuel adhering to the wall decreases. As a result, deterioration of emissions is suppressed.

[0081] (2) By performing the injection interval change process, intake stroke injection and compression stroke injection are more likely to be performed after the vibration of the components that occurs when the injector 51 is closed has subsided. As a result, variations in injection volume are reduced, and the amount of fluctuation in output torque is reduced.

[0082] (3) Once the amount of change in the first intake stroke injection ratio and the amount of change in the first compression stroke injection ratio reach the first threshold determined for each, no further changes in the first intake stroke injection ratio and the first compression stroke injection ratio are performed. Therefore, it is possible to suppress an increase in the amount of top surface deposition caused by the first intake stroke injection ratio and the first compression stroke injection ratio becoming excessively large. As a result, deterioration of emissions associated with the execution of the injection ratio change process is less likely to occur.

[0083] (4) After the amount of change in the injection interval for the intake stroke injection and the amount of change in the injection interval for the compression stroke injection reach the second threshold set for each, no further changes in the injection interval for the intake stroke injection and the injection interval for the compression stroke injection are performed. Therefore, it is possible to suppress an increase in wall adhesion caused by excessively large changes in the injection interval for the intake stroke injection and the injection interval for the compression stroke injection. As a result, deterioration of emissions associated with the execution of the injection interval change process is less likely to occur.

[0084] (5) By performing the injection frequency change process, the amount injected per injection gradually increases. As a result, the variation in injection amount decreases, and the amount of fluctuation in output torque decreases. In particular, if at least one FL injection can be performed, the amount of fluctuation in output torque will decrease even further.

[0085] (6) When performing the injection count change process, the control device 100 stops the second intake stroke injection first, and stops the second compression stroke injection first, of the first and second compression stroke injections. As a result, deterioration of emissions due to a large amount of material adhering to the wall surface is less likely to occur.

[0086] (7) Since the injection ratio change process, injection interval change process, and injection number change process are executed in that order, it is possible to reduce the amount of fluctuation in output torque while suppressing the deterioration of emissions.

[0087] <Example of changes> The above disclosure may be implemented with modifications as follows. The above disclosure and the following examples of modifications may be combined with each other to the extent that they do not conflict with each other technically.

[0088] The injection ratios for the first intake stroke and the second intake stroke, or the injection ratios for the first compression stroke and the second compression stroke, may be the only ones to be modified by the injection ratio modification process. The injection intervals for the first intake stroke and the second intake stroke, or the injection intervals for the first compression stroke and the second compression stroke, may be the only ones to be modified by the injection interval modification process.

[0089] The number of injections for the first intake stroke and the second intake stroke, or the number of injections for the first compression stroke and the second compression stroke, may be the only ones to be modified by the injection count modification process.

[0090] The explanation described a case where the number of injections before the injection count change process was modified involved 3 intake stroke injections and 2 compression stroke injections. However, the number of intake stroke injections and compression stroke injections can be any number, as long as each is 2 or more. [Explanation of Symbols]

[0091] 10...Internal combustion engine, 11...Cylinder, 12...Piston, 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, wherein the system performs multiple intake stroke injections, which are fuel injections within the range from the start to the end of the intake stroke, and multiple compression stroke injections, which are fuel injections within the range from the start to the end of the compression stroke, In at least one of the intake stroke injection and the compression stroke injection, the first injection is configured such that the period between the injection timing of the first injection and the top dead center timing (the time when the piston in the cylinder is at top dead center) is the shortest, and the second injection is configured such that the period between the injection timing of the second injection and the top dead center timing is longer than that of the first injection. The control device is When the amount of fluctuation in the output torque of the internal combustion engine exceeds a predetermined amount, an injection ratio modification process is executed to change the first injection ratio and the second injection ratio so that the first injection ratio, which is the ratio of the injection amount of the first injection to the total injection amount (the sum of the injection amounts of the first and second injections), is greater than the second injection ratio, which is the ratio of the injection amount of the second injection to the total injection amount. Fuel injection device.

2. When the amount of variation is greater than or equal to the predetermined amount of variation, the control device changes the first injection ratio and the second injection ratio of the intake stroke injection in the injection ratio change process. The fuel injection device according to claim 1.

3. The control device is When the amount of change in the first injection ratio and the second injection ratio, which are changed in the injection ratio changing process, reaches a first threshold, and the amount of change is equal to or greater than the predetermined amount of change, an injection interval changing process is executed to change the injection interval by changing the injection timing of the second injection so that the injection interval, which is the period between the injection timing of the first injection and the injection timing of the second injection, becomes longer. A fuel injection device according to claim 1 or claim 2.

4. The control device is When the amount of change in the injection interval that is changed in the injection interval change process reaches a second threshold, and the amount of change is equal to or greater than the predetermined amount of change, the injection count change process is executed to change the number of fuel injections by stopping the second injection. The fuel injection device according to claim 3.

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