Engine system

Abstract

To properly correct an injection quantity of a gas fuel.SOLUTION: An engine system 1 includes: branch passages 4a, 4b, 4c, 4d respectively connected to cylinders 21, 22, 23, 24; injectors 15, 16, 17, 18 for respectively injecting a gas fuel into the branch passages 4a, 4b, 4c, 4d; and a controller 100 for controlling the injectors 15, 16, 17, 18. The controller 100 corrects a fuel quantity that excesses or runs short due to the jetted gas fuel flowing into other branch passages relative to an injection quantity of a gas fuel to be injected to any one of the branch passages.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to control of an engine system. [Background Art]

[0002] In a fuel injection system provided in an internal combustion engine, a technique for setting an injection amount of gaseous fuel in accordance with an operating state of an engine is known. For example, Japanese Unexamined Patent Application Publication No. 2013-213440 (Patent Document 1) discloses a technique that calculates a basic injection amount of gaseous fuel based on an engine speed and an intake air amount, and corrects the basic injection amount based on a pressure in a gas tank during a transient change. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2013-213440 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] In the combustion injection system as described above, when gaseous fuel is used as fuel, unlike a case where liquid fuel is used, the volume of the fuel is large, so that not all of the injected fuel is introduced into a cylinder, and a part of the fuel may flow into other cylinders. Particularly during transient operation, excess or deficiency may occur with respect to a requested injection amount that changes over time due to the gaseous fuel flowing into other cylinders and the gaseous fuel flowing in from other cylinders. As a result, there is a possibility that the air-fuel ratio deviates from a target air-fuel ratio (for example, the air-fuel ratio corresponding to stoichiometry).

[0005] The present invention has been made to solve the problem described above, and an object of the present invention is to provide an engine system that appropriately corrects an injection amount of gaseous fuel. [Means for Solving the Problem]

[0006] An engine system according to one aspect of this invention comprises a plurality of intake passages each connected to a plurality of cylinders, a plurality of injection devices for injecting gaseous fuel into each of the plurality of intake passages, and a control device for controlling the plurality of injection devices. The control device corrects the amount of gaseous fuel injected into one of the plurality of intake passages by the amount of fuel that is in excess or insufficient due to the injected gaseous fuel flowing back into the other intake passages.

[0007] In this way, by correcting for the excess or deficiency of fuel that occurs when some of the gaseous fuel flows into other intake passages when it is injected from the injector, it is possible to suppress excess or deficiency in the injection amount even during transient operation and suppress deviations in the air-fuel ratio.

[0008] In one embodiment, the control device calculates a correction value corresponding to the amount of fuel that is in excess or insufficient due to flowing into other intake passages, using the correlation between the first injection amount required in the first cylinder, which is in the intake stroke, and the difference between the first injection amount and the second injection amount required in the second cylinder, which is in the most recent intake stroke preceding the first cylinder.

[0009] In this way, by calculating a correction value using the correlation between the first injection amount and the difference, it is possible to accurately correct for fuel surpluses or deficits caused by gaseous fuel flowing into other intake passages. This makes it possible to suppress deviations in the air-fuel ratio even during transient operation.

[0010] In one further embodiment, when performing synchronous injection during the intake stroke of each cylinder, the control device calculates a basic value for the injection amount to achieve the target air-fuel ratio, calculates the difference in injection amount between the previous basic value and the current basic value, calculates a correction value based on the current basic value and the injection amount difference, corrects the current basic value with the correction value, and performs the current synchronous injection.

[0011] In this way, even during transient operation, deviations in the air-fuel ratio can be suppressed by calculating a correction value for the injection amount.

[0012] In one further embodiment, when performing synchronous injection for the intake stroke of each cylinder, the control device foresees fluctuations in the intake manifold pressure in the intake passage based on the throttle opening, calculates a predicted value for the intake manifold pressure, calculates the pressure difference between the previous predicted value and the current predicted value, calculates a pressure correction value based on the current predicted value and the pressure difference, corrects the current predicted value with the pressure correction value, calculates the injection amount based on the corrected predicted value, and performs the current synchronous injection.

[0013] In this way, even during transient operation, deviations in the air-fuel ratio can be suppressed by calculating a correction value for the predicted value. [Effects of the Invention]

[0014] This invention provides an engine system that appropriately corrects the amount of gaseous fuel injected. [Brief explanation of the drawing]

[0015] [Figure 1] This figure shows an example of a schematic configuration of the engine system according to this embodiment. [Figure 2] This diagram illustrates an example of how to set the injection amount when the engine system is in a transient operating state. [Figure 3] This diagram illustrates an example of gaseous fuel leakage into other cylinders during steady-state operation. [Figure 4] This diagram illustrates an example of gaseous fuel leakage into other cylinders during acceleration. [Figure 5] This diagram illustrates an example of gaseous fuel leaking into other cylinders during rapid acceleration. [Figure 6] This is a flowchart illustrating an example of the process of setting a function f(n). [Figure 7] This diagram illustrates an example of the process of setting a function f(n). [Modes for carrying out the invention]

[0016] The present embodiment will be described below with reference to the drawings. In the following description, the same reference numerals are assigned to the same components. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[0017] FIG. 1 is a diagram showing an example of a schematic configuration of an engine system 1 according to the present embodiment. As shown in FIG. 1, the engine system 1 includes an engine body 2, an intake manifold (hereinafter referred to as an intake manifold) 4, an intake pipe 6, a throttle valve 20, and a control device 100. The engine system 1 is, for example, mounted on a mobile body such as a vehicle and configured by an internal combustion engine that operates using gaseous fuel. In the present embodiment, a case where the gaseous fuel is, for example, hydrogen will be described as an example.

[0018] A plurality of cylinders constituted by, for example, a cylinder block and a cylinder head are formed in the engine body 2. In the present embodiment, the engine body 2 is provided with hollow cylindrical cylinders 21, 22, 23, and 24 at four locations, for example. In each of the cylinders 21, 22, 23, and 24, a piston (not shown) is provided slidably along the opening direction (the front-back direction of the paper surface of FIG. 1) in the cylinder. One end of a piston rod (not shown) corresponding to each piston is connected to each piston. The other end of each piston rod is connected to a crankshaft (not shown), and a crank mechanism is configured in each cylinder. When the piston of each cylinder slides in the cylinder, the crankshaft rotates. In the present embodiment, the description will be given with cylinder 21 as the "#1" cylinder, cylinder 22 as the "#2" cylinder, cylinder 23 as the "#3" cylinder, and cylinder 24 as the "#4" cylinder.

[0019] The engine body 2 further includes intake ports 31, 32, 33, 34. One end of each of the intake ports 31, 32, 33, 34 is connected to the top of a corresponding one of the cylinders 21, 22, 23, 24, respectively. Intake valves 25, 26, 27, 28 are respectively provided between the intake ports 31, 32, 33, 34 and the cylinders 21, 22, 23, 24. For example, when the intake valve 25 is closed, a cut-off state is established in which communication between the intake port 31 and the cylinder 21 is cut off; when the intake valve 25 is opened, a communication state is established in which the intake port 31 and the cylinder 21 communicate with each other. The intake valves 26, 27, 28 also have the same structure and function as the intake valve 25, and detailed description thereof will not be repeated.

[0020] Further, a plurality of spark plugs (not shown) are provided at each of the tops of the cylinders 21, 22, 23, 24. The plurality of spark plugs perform ignition operations according to a predetermined ignition order in response to a control signal from a control device 100. For example, the control device 100 causes the spark plug of the cylinder among the cylinders 21, 22, 23, 24 that has completed the compression stroke to perform an ignition operation. For example, the control device 100 performs ignition operations in the order of the cylinder 21 (#1), the cylinder 23 (#3), the cylinder 24 (#4), and the cylinder 22 (#2). The above-described ignition order is merely an example, and is not particularly limited to this order.

[0021] Furthermore, a plurality of exhaust ports (not shown) are respectively connected to each of the tops of the cylinders 21, 22, 23, 24. Exhaust valves 35, 36, 37, 38 are respectively provided between the cylinders 21, 22, 23, 24 and the plurality of exhaust ports. For example, when the exhaust valve 35 is closed, communication between the exhaust port and the cylinder 21 is in a cut-off state, and when the exhaust valve 35 is opened, communication between the exhaust port and the cylinder 21 is in a communication state. The exhaust valves 36, 37, 38 also have the same structure and function as the intake valve 25, and detailed description thereof will not be repeated.

[0022] It should be noted that the plurality of exhaust ports are connected to one end (not shown) of an exhaust pipe via an exhaust manifold (not shown). The other end of the exhaust pipe is connected to an exhaust purification device that purifies exhaust gas and a muffler such as a silencer (none of which are shown).

[0023] The intake manifold 4 includes branch passages 4a, 4b, 4c, and 4d, and a surge tank 4e. One end of each branch passage 4a, 4b, 4c, and 4d is connected to the surge tank 4e. The other end of each branch passage 4a, 4b, 4c, and 4d is connected to the other end of the intake ports 31, 32, 33, and 34, respectively. One end of the intake pipe 6 is connected to the surge tank 4e. The intake pipe 6 is provided with a throttle valve 20. The throttle valve 20 is configured to adjust the flow rate of intake air flowing through the intake pipe 6 in response to a control signal from the control device 100. The intake manifold 4, the intake pipe 6, and the intake ports 31, 32, 33, and 34 constitute the "intake passage".

[0024] Each of the branch passages 4a, 4b, 4c, and 4d is provided with an injection device 15, 16, 17, and 18, respectively. The injection devices 15, 16, 17, and 18 may be provided at the intake ports 31, 32, 33, and 34, respectively, or they may be provided around the top of cylinders 21, 22, 23, and 24, configured to directly inject gaseous fuel into the cylinders.

[0025] Injectors 15, 16, 17, and 18 inject gaseous fuel into branch passages 4a, 4b, 4c, and 4d, respectively, in response to control signals from the control device 100. The control device 100 injects the required amount of gaseous fuel into the cylinders 21, 22, 23, and 24 during the intake stroke (i.e., performs synchronous injection). The control device 100 controls the amount injected into the branch passages by, for example, adjusting the injection time of the gaseous fuel from the injectors. That is, the control device 100 controls the injectors 15, 16, 17, and 18 to inject for only the injection time set according to the state of the engine system 1.

[0026] The control device 100 is connected to an intake pressure sensor 102, a crank angle sensor 104, and an intake air volume sensor 106. The intake pressure sensor 102 detects the intake manifold pressure in the intake manifold 4 and transmits a signal indicating the detected intake manifold pressure to the control device 100. The crank angle sensor 104 detects the rotation angle of the crankshaft (hereinafter referred to as the crank angle) and transmits a signal indicating the detected crank angle to the control device 100. Furthermore, the intake air volume sensor 106 detects the flow rate of intake air circulating through the intake manifold 6 (hereinafter referred to as the intake air volume) and transmits a signal indicating the detected intake air volume to the control device 100.

[0027] The control device 100 includes a CPU (Central Processing Unit) that performs various processes, and memory (not shown) that includes ROM (Read Only Memory) for storing programs and data, and RAM (Random Access Memory) for storing the processing results of the CPU, etc.

[0028] The control device 100 controls various components (for example, the injection devices 15, 16, 17, 18 and the throttle valve 20, etc.) so that the engine system 1 reaches a desired operating state, based on signals from various sensors (for example, the intake pressure sensor 102, crank angle sensor 104, or intake air volume sensor 106, etc.) and maps and programs stored in memory. The various processes performed by the control device 100 are not limited to software-based processing; they can also be performed using dedicated hardware (electronic circuits).

[0029] When the engine system 1 having the above configuration is in operation, intake stroke, compression stroke, expansion stroke, and exhaust stroke are performed in each of the cylinders 21, 22, 23, and 24. These strokes are performed in cylinders 21, 22, 23, and 24 at timings that are shifted by a predetermined crank angle.

[0030] For example, when the crank angle corresponds to the intake stroke of cylinder 21, the intake valve 25 of cylinder 21 opens and the exhaust valve 35 closes due to the operation of a cam mechanism (not shown). At this time, as the piston inside cylinder 21 slides toward bottom dead center, negative pressure is created inside the cylinder, and intake air and gaseous fuel injected from the injection device 15 are introduced into cylinder 21.

[0031] When the piston reaches the crank angle corresponding to near bottom dead center, that is, the crank angle corresponding to the compression stroke, the intake valve 25 and exhaust valve 35 close due to the operation of the cam mechanism. At this time, the air-fuel mixture in cylinder 21 is compressed as the piston slides toward top dead center.

[0032] When the piston reaches the crank angle corresponding to near top dead center, that is, the crank angle corresponding to the expansion stroke (combustion stroke), the spark plug ignites. The spark plug ignites, causing the fuel-air mixture in cylinder 21 to burn, and the resulting combustion pressure pushes the piston down, which in turn rotates the crankshaft via the crank mechanism.

[0033] When the piston reaches a crank angle corresponding to near bottom dead center, that is, the crank angle corresponding to the exhaust stroke, the cam mechanism operates, closing the intake valve 25 and opening the exhaust valve 35. At this time, the piston slides toward top dead center, increasing the pressure inside cylinder 21, and the gas inside cylinder 21 is discharged to the exhaust port.

[0034] The series of cycles consisting of the intake stroke, compression stroke, expansion stroke, and exhaust stroke described above are performed in the order of cylinder 21 (#1), cylinder 23 (#3), cylinder 24 (#4), and cylinder 22 (#2) at timings shifted by a predetermined crank angle. The operation of each stroke in the other cylinders 22, 23, and 24 is the same as the operation of each stroke in cylinder 21, so a detailed explanation will not be repeated.

[0035] When the engine system 1 operates through the processes described above, it is particularly important that an appropriate amount of gaseous fuel is supplied from the injector to each branch passage during the intake stroke. The appropriate injection amount corresponds to, for example, the amount of gaseous fuel required to meet the output demanded by the driver or control device 100, and to bring the air-fuel ratio to a target air-fuel ratio (for example, the air-fuel ratio corresponding to stoichiometry).

[0036] For example, when the engine system 1 is in a steady state (a state where the required output or load is constant), the control device 100 sets the injection time (injection amount) using a map of engine speed, intake manifold pressure, and injection time. The control device 100, for example, obtains the rate of change of the crank angle per predetermined time using the detection result of the crank angle sensor 104, and calculates the engine speed from the obtained rate of change of the crank angle per predetermined time. The map of engine speed, intake manifold pressure, and injection time is adapted to the injection time that satisfies the required output and air-fuel ratio in an operating state determined in advance by experiments, etc., based on the engine speed and intake manifold pressure.

[0037] On the other hand, if the operating state of engine system 1 is a transient state (a state in which the required output changes), the required output (more specifically, the intake manifold pressure) will change even if the above-mentioned map is used, which may cause a delay in supplying the appropriate injection amount. For this reason, it is conceivable to calculate a predicted value of the intake manifold pressure from changes in the throttle valve opening (hereinafter referred to as throttle opening), and then set the injection time based on the calculated predicted value of the intake manifold pressure and the engine speed.

[0038] Figure 2 illustrates an example of how to set the injection amount when the operating state of engine system 1 is in a transient state. The horizontal axis of Figure 2 represents time. The vertical axis of Figure 2 represents throttle opening, intake manifold pressure, and air-fuel ratio (A / F). LN1 (solid line) in Figure 2 shows the change in throttle opening. LN2 (solid line) in Figure 2 shows the change in the measured value of intake manifold pressure (hereinafter referred to as actual intake manifold pressure). LN3 (dashed line) in Figure 2 shows the change in the predicted value of intake manifold pressure. LN4 (solid line) in Figure 2 shows the change in air-fuel ratio due to the injection amount set based on the actual intake manifold pressure. LN5 (dashed line) in Figure 2 shows the change in air-fuel ratio due to the injection amount set based on the predicted value of intake manifold pressure.

[0039] As shown in LN1 of Figure 2, when the throttle opening increases at time T(0), the actual intake manifold pressure increases with a delay compared to the increase in throttle opening, as shown in LN2 of Figure 2. Therefore, when an injection amount is set corresponding to the actual intake manifold pressure, the amount of gaseous fuel injected tends to be insufficient because the intake manifold pressure has increased further from the actual intake manifold pressure at the time the injection amount was set. As a result, the air-fuel ratio changes significantly towards the lean side, as shown in LN4 of Figure 2.

[0040] To address this problem, one approach is to set the injection amount using a predicted value of the intake manifold pressure calculated from the change in throttle opening. For example, as shown in LN3 in Figure 2, a predicted value of the intake manifold pressure after a predetermined time (look-ahead time) from the current point in time is calculated. For instance, using the throttle opening and engine speed at time T(1), a predicted value of the intake manifold pressure at time T(2), after a predetermined time has elapsed from time T(1), is calculated. Then, by setting the injection amount at time T(1) using the calculated predicted value, an appropriate amount of gaseous fuel corresponding to the predicted value can be supplied to the branch passage when gaseous fuel is injected. As a result, insufficient injection amount at time T(2) can be suppressed. Consequently, as shown in LN5 in Figure 2, the amount of change towards the lean side of the air-fuel ratio can be suppressed compared to the change in the air-fuel ratio shown in LN4 in Figure 2.

[0041] However, when gaseous fuel is used as fuel, unlike when liquid fuel is injected, the volume of the fuel is large, and not all of the injected fuel may be introduced into the cylinder. Specifically, as shown in Figure 1, some of the gaseous fuel injected into branch passage 4b ​​may divert to other branch passages (for example, branch passage 4a), resulting in not all of the injected gaseous fuel being introduced into the target cylinder.

[0042] For example, consider a case where a portion of the injected gaseous fuel flows entirely to the cylinder that will next undergo the intake stroke. Figure 3 illustrates an example of gaseous fuel flowing to other cylinders during steady-state operation. LN6 in Figure 3 shows the change in the appropriate injection amount according to the operating state. As shown in Figure 3, during steady-state operation, the appropriate injection amount according to the operating state remains constant, and therefore the amount of gaseous fuel actually supplied to each cylinder also remains constant.

[0043] At this time, as shown in Figure 3(a-1), a portion of the gaseous fuel injected towards cylinder 21(#1) flows back to cylinder 23(#3), which is in the next intake stroke. In this case, as shown in Figure 3(a-2), a portion of the fuel injected towards cylinder 23(#3) flows back to cylinder 24(#4), which is in the next intake stroke, and a similar amount of gaseous fuel flows back from cylinder 21(#1), which is in the previous intake stroke. As a result, the amount of gaseous fuel corresponding to the operating state is supplied to cylinder 23. Similarly, in Figures 3(a-3), 3(a-4), 3(a-5), and 3(a-6), even if a portion flows back to the cylinder in the next intake stroke, a similar amount of gaseous fuel flows back from the cylinder in the previous intake stroke. As a result, the amount of gaseous fuel corresponding to the operating state is supplied to each cylinder, making it possible to maintain the target air-fuel ratio.

[0044] On the other hand, during transient operation, the appropriate injection amount changes for each cylinder, so when gaseous fuel flows back from the cylinder in the previous intake stroke, there may be an excess or deficiency in the amount of fuel introduced into the cylinder relative to the appropriate injection amount.

[0045] For example, during transient operation such as acceleration, the amount of fuel introduced into the cylinder may be insufficient compared to the appropriate injection amount due to leakage of gaseous fuel. Figure 4 is a diagram illustrating an example of leakage of gaseous fuel to other cylinders during acceleration. LN7 in Figure 4 shows the change in the appropriate injection amount according to the operating state. As shown in Figure 4, during transient operation during acceleration, the appropriate injection amount increases in each cylinder according to the order of the cylinders undergoing the intake stroke.

[0046] In this case, for example, as shown in (b-0) and (b-1) of Figure 4, we can assume that a portion of the gaseous fuel that has been circulated from cylinder 22 is introduced into cylinder 21 (#1). At this time, a portion of the amount of fuel injected into cylinder 21 is circulated into cylinder 23 (#3), which is in the next intake stroke. Then, the fuel that has circulated from cylinder 22 (#3), which is in the previous intake stroke, is introduced into cylinder 21 (#1).

[0047] In the next intake stroke, cylinder 23 (#3) will be injected with a larger amount of fuel than that injected into cylinder 21 (#1) due to the increased power required. However, since there is an upper limit to the amount of fuel that can be introduced into cylinder 23 (#3) from the intake valve 27, the excess amount of gaseous fuel flows back into cylinder 24 (#4) for the next intake stroke. Meanwhile, cylinder 23 (#3) receives fuel that has flowed back in from cylinder 21 (#1). As a result, the amount of fuel introduced into cylinder 23 (#3) is insufficient by the amount shown in the dashed rectangle in Figure 4 (b-2). Consequently, the air-fuel ratio becomes leaner than the target air-fuel ratio.

[0048] Similarly, in cylinder 24 (#4), which is in the next intake stroke, a larger amount of fuel is injected than the amount injected into cylinder 23 (#3) due to the further increase in required power. However, as mentioned above, there is an upper limit to the amount of fuel that can be introduced into cylinder 24 (#4) from the intake valve 28, so the amount of gaseous fuel exceeding that limit flows back into cylinder 22 (#2) in the next intake stroke. Meanwhile, cylinder 24 (#4) receives fuel that has flowed back in from cylinder 23 (#3). As a result, the amount of fuel introduced into cylinder 24 (#4) is insufficient by the amount shown in the dashed rectangle in Figure 4 (b-3). Consequently, the air-fuel ratio becomes leaner than the target air-fuel ratio.

[0049] Similarly, in Figure 4 (b-4) and (b-5), when some of the gaseous fuel exceeding the upper limit flows into the cylinder in the next intake stroke, a larger amount of gaseous fuel flows into the next intake stroke than the amount that flowed in from the previous intake stroke cylinder. As a result, the amount of gaseous fuel introduced into the cylinder in the current intake stroke is insufficient, and the air-fuel ratio becomes leaner than the target air-fuel ratio.

[0050] Furthermore, regarding (b-6) in Figure 4, as with steady-state operation, the appropriate injection amount according to the operating state becomes the same as the injection amount in the cylinder of the previous intake stroke. As a result, the amount of gaseous fuel flowing to the cylinder of the next intake stroke is approximately the same as the amount of gaseous fuel flowing from the cylinder of the previous intake stroke, thus eliminating the shortage of gaseous fuel. Thus, during transient operation such as acceleration, the increase in required power causes a large amount of gaseous fuel to flow to the cylinder of the next intake stroke, resulting in a shortage of gaseous fuel in the cylinder of the current intake stroke. Consequently, the air-fuel ratio becomes leaner than the target air-fuel ratio.

[0051] Furthermore, during transient operations such as deceleration, the amount of fuel introduced into the cylinder may be excessive compared to the appropriate injection amount. This is because, as the required power decreases over time and the appropriate injection amount decreases, the amount of fuel flowing back from the cylinder in the previous intake stroke becomes greater than the amount of fuel flowing back to the cylinder in the next intake stroke. As a result, the air-fuel ratio becomes richer than the target air-fuel ratio.

[0052] Thus, during transient operation, if gaseous fuel flows back into the cylinder for the next intake stroke, the air-fuel ratio may deviate from the target air-fuel ratio (for example, the air-fuel ratio corresponding to stoichiometry) and become unstable.

[0053] Therefore, in this embodiment, the control device 100 corrects the amount of gaseous fuel injected into one of the branch passages 4a, 4b, 4c, and 4d by the amount of fuel that is in excess or insufficient due to the injected gaseous fuel flowing into the other branch passages.

[0054] This method suppresses excess or insufficient injection volume even during transient operation, thereby preventing deviations in the air-fuel ratio.

[0055] The specific correction method is explained in detail below. The amount of fuel insufficient in each cylinder during transient operation is thought to correlate with the difference (hereinafter also referred to as Δ injection amount) between the amount of gaseous fuel injected for the current intake stroke (hereinafter also referred to as the first injection amount) and the amount of gaseous fuel injected for the cylinder in the previous intake stroke (hereinafter also referred to as the second injection amount), as shown in the dashed rectangle in Figure 4. Furthermore, the amount of fuel insufficient in each cylinder during transient operation is thought to correlate with the first injection amount as well.

[0056] Figure 5 illustrates an example of gaseous fuel leakage to multiple cylinders during rapid acceleration. LN8 in Figure 5 shows the appropriate injection amount change according to the operating conditions during rapid acceleration, where the acceleration requirement is even greater than that shown in Figure 4.

[0057] During rapid acceleration, the gaseous fuel injected into the cylinder undergoing the current intake stroke will not only reach the next cylinder undergoing the intake stroke, but also the cylinder undergoing the stroke after that.

[0058] For example, the gaseous fuel recirculation shown in (c-0) and (c-1) of Figure 5 is similar to that shown in (b-0) and (b-1) of Figure 4, so a detailed explanation will not be repeated.

[0059] In the next intake stroke, cylinder 23 (#3) will be injected with a larger amount of fuel than that injected into cylinder 21 (#1) due to the increased power required. However, since there is an upper limit to the amount of fuel that can be introduced into cylinder 23 (#3) from the intake valve 27, the excess amount of gaseous fuel flows back into cylinder 24 (#4) for the next intake stroke. Meanwhile, cylinder 23 (#3) receives fuel that has flowed back in from cylinder 21 (#1). As a result, the amount of fuel introduced into cylinder 23 (#3) is insufficient by the amount shown in the dashed rectangle in Figure 5 (c-2).

[0060] Furthermore, in the next intake stroke, cylinder 24 (#4), due to a further increase in the required power, cylinder 23 ( #3 A larger amount of fuel is injected into cylinder 24 than the amount of gaseous fuel injected into cylinder 23. As a result, the amount of gaseous fuel exceeding the upper limit of the amount of fuel that can be introduced flows back into cylinder 22 (#2) in the next intake stroke and into cylinder 21 (#1) in the intake stroke after that. Meanwhile, fuel that has flowed back from cylinder 23 (#3) is introduced into cylinder 24 (#4). As a result, the amount of fuel introduced into cylinder 24 (#4) is insufficient by the amount shown in the dashed rectangle in (c-3) of Figure 5.

[0061] Furthermore, in the next intake stroke of cylinder 22 (#2), the amount of gaseous fuel injected towards cylinder 22 (#2) that exceeds the upper limit of the amount of fuel that can be introduced flows back to cylinder 21 (#1) in the next intake stroke and then to cylinder 23 (#3) in the intake stroke after that. Meanwhile, fuel that has flowed back from cylinder 24 (#4) is introduced into cylinder 22 (#2). As a result, the amount of fuel introduced into cylinder 22 (#2) is insufficient by the amount shown in the dashed rectangle in (c-4) of Figure 5.

[0062] Furthermore, in the next intake stroke of cylinder 21 (#1), the amount of gaseous fuel injected towards cylinder 21 (#1) that exceeds the upper limit of the amount of fuel that can be introduced flows back to cylinder 23 (#3) in the next intake stroke and then to cylinder 24 (#4) in the intake stroke after that. Meanwhile, cylinder 21 (#1) receives fuel that has flowed back from cylinder 22 (#22) and fuel that has flowed back from cylinder 24 (#4). As a result, the amount of fuel introduced into cylinder 21 is insufficient by the amount shown in the dashed rectangle in (c-5) of Figure 5.

[0063] Thus, during transient operation, if the injection amount is large, such as during rapid acceleration, gaseous fuel may circulate to cylinders other than those in the next intake stroke. Therefore, the amount of gaseous fuel circulating is thought to correlate not only with the Δ injection amount mentioned above, but also with the amount of gaseous fuel injected to the cylinder in the current intake stroke (first injection amount).

[0064] Therefore, in this embodiment, the control device 100 calculates a correction value corresponding to the amount of fuel that is in excess or insufficient due to the fuel flowing to other cylinders, using the correlation between the first injection amount and the Δ injection amount.

[0065] The control device 100 calculates the excess or deficiency of fuel using a function f(first injection amount, Δ injection amount) with the first injection amount and Δ injection amount as parameters, and sets the calculated excess or deficiency of fuel as a correction value C(n). In the following description, the first injection amount is Tau(n), the second injection amount is Tau(n-1), and the Δ injection amount is ΔTau(n) (=Tau(n)-Tau(n-1)), and the control device 100 calculates the correction value C(n) using the formula C(n)=f(Tau(n), ΔTau(n)). The function f(n) is set, for example, using data acquired when the engine system 1 is operated to maintain a target air-fuel ratio for each of the set operating conditions, after setting multiple operating conditions for a predetermined engine speed and intake manifold pressure.

[0066] As a specific method for setting the function f(n), for example, one can use a method of modeling (functionizing) the data obtained by experimental design according to the multiple operating conditions described above using the response surface method. In the following explanation, we will describe as an example how to set the function f(n) when it is expressed as a linear equation with Tau(n) and ΔTau(n) as parameters.

[0067] For example, if the function f(n) is a linear expression with Tau(n) and ΔTau(n) as parameters, the function f(n) can be expressed by the equation f(n) = a × Tau(n) + b × ΔTau(n) + c (constant). Then, by setting the coefficients a, b and the constant c using data obtained through the experiment described above, it is possible to set the function f. Furthermore, as for the response surface method, any known technique can be used, and a detailed explanation will not be provided, but for example, the model can be created using methods that calculate an approximate formula from multiple discrete data using least squares method, interpolation method, or AI (Artificial Intelligence) such as machine learning.

[0068] Furthermore, various correlation coefficients, such as R-squared, can be calculated for the modeled function f(n), and the suitability of the correction value C(n) calculated from the function f(n) and its parameters can be verified using the calculated correlation coefficients. For example, if the correlation coefficient between the acquired data and the data calculated from the function f(n) and its parameters is within a predetermined range, it becomes possible to correct the injection amount using the correction value C(n) calculated from the function f(n) and its parameters even under operating conditions other than the multiple pre-set operating conditions, and it becomes possible to implement a process to calculate the correction value C(n) using the function f(n) set for the control device 100. In this embodiment, the case where the function f(n) is represented as a linear equation is described as an example, but it may also be represented as a higher-order equation such as a quadratic equation.

[0069] The following describes an example of the process of setting the function f(n), referring to Figure 6. Figure 6 is a flowchart illustrating an example of the process of setting the function f(n). Information about the results and conditions calculated in these processes is stored in a memory device such as a personal computer. Furthermore, the calculations of the results of these processes are performed using the CPU of a personal computer.

[0070] In step 100 (hereinafter referred to as S), multiple driving conditions are set. These multiple driving conditions include, for example, engine speed conditions and acceleration / deceleration conditions. The engine speed condition is the engine speed condition maintained during the experiment. The engine speed condition includes, for example, one of several predetermined speeds (e.g., 1500 rpm, 2000 rpm, or 2500 rpm). The acceleration / deceleration condition includes, for example, a condition indicating how the accelerator opening will change over a predetermined period. The acceleration / deceleration condition includes, for example, a condition to change the accelerator opening from 20% to 45%, a condition to change the accelerator opening from 20% to 100% (full throttle), or a condition to change the accelerator opening from 45% to 100% (full throttle). The number of conditions set is set to a number that can be modeled from the measured parameter data obtained by the experiment described later. In S100, one of the pre-set operating conditions for which experimental data has not yet been obtained is selected. The process then proceeds to S102.

[0071] In S102, the engine system 1 is operated multiple times according to the set operating conditions, and various experimental data are acquired. During the operation of the engine system 1, for example, the predicted value of the intake manifold pressure and the injection amount are adjusted so that the air-fuel ratio is maintained at a target air-fuel ratio. The air-fuel ratio is acquired using, for example, an air-fuel ratio sensor (not shown). For example, the control device 100 may adjust the predicted value of the intake manifold pressure and the injection amount using the detection result of the air-fuel ratio sensor so that the air-fuel ratio is maintained at a target air-fuel ratio. The various data, as described above, are data for setting the function f (i.e., data for setting coefficients a, b and constant c), and include data on the adjusted first injection amount Tau(n) and Δ injection amount ΔTau(n) (i.e., data on the adjusted first injection amount Tau(n) and second injection amount Tau(n-1)), and data on the actual intake manifold pressure and the predicted value of the intake manifold pressure.

[0072] In S104, when operating engine system 1 according to the operating conditions set using various acquired data, a correction value for the injection amount and a correction value for the predicted intake manifold pressure are calculated from the injection amount and intake manifold pressure to maintain the air-fuel ratio at the target air-fuel ratio. For example, the correction value for the injection amount is calculated using the difference between the injection amount before adjustment and the injection amount after correction. Similarly, the correction value for the predicted intake manifold pressure is calculated using the difference between the predicted intake manifold pressure before adjustment and the predicted intake manifold pressure after correction.

[0073] In S106, the correction value for the injection amount and the correction value for the predictive intake manifold pressure, calculated in accordance with the set operating conditions, are stored.

[0074] In S108, it is determined whether or not various correction values ​​have been calculated for all driving conditions. If all of the various correction values ​​corresponding to the pre-set driving conditions have been calculated, it is determined that correction values ​​have been calculated for all driving conditions. If it is determined that correction values ​​have been calculated for all driving conditions (YES in S108), the process moves to S110. If it is determined that correction values ​​have not been calculated for all driving conditions (NO in S108), the process returns to S100.

[0075] In S110, the function f(n) for calculating the aforementioned correction value C(n) is calculated using the calculated correction value. That is, the coefficients a, b and the constant c of the aforementioned linear equation that constitute the function f(n) are calculated from the acquired data. The method for calculating the coefficients a, b and the constant c is as described above, so a detailed explanation will not be repeated.

[0076] In this embodiment based on the structure and flowchart described above, an example of the operation in which the function f(n) for calculating the correction value C(n) is set will be explained with reference to Figure 7. Figure 7 is a diagram illustrating an example of the operation in which the function f(n) is set. Figure 7 shows an example of the operating state during acceleration. The vertical axis of Figure 7 shows the throttle opening, fuel injection amount, intake manifold pressure, and air-fuel ratio (A / F). The horizontal axis of Figure 7 shows time. LN9 in Figure 7 shows the change in throttle opening. LN10 (thick solid line) in Figure 7 shows the change in injection amount after correction. LN11 (thin solid line) in Figure 7 shows the change in injection amount before correction. LN12 (dotted line) in Figure 7 shows the change in the predicted value of intake manifold pressure after correction. LN13 (dashed line) in Figure 7 shows the change in the predicted value of intake manifold pressure before correction. LN14 (solid line) in Figure 7 shows the change in the actual intake manifold pressure. LN15 (solid line) in Figure 7 shows the change in air-fuel ratio when the injection amount is set based on the actual intake manifold pressure. LN16 (dashed line) in Figure 7 shows the change in air-fuel ratio when the injection amount is set based on the predicted intake manifold pressure. LN17 (dotted line) in Figure 7 shows the change in air-fuel ratio when the injection amount is set based on the corrected predicted intake manifold pressure.

[0077] For example, when one of several operating conditions is set (S100), the engine system 1 is operated according to the set operating condition. In this case, for example, suppose the operating condition is set such that when the engine speed is predetermined, the throttle opening is changed as shown in LN9 in Figure 7, causing the actual intake manifold pressure to change as shown in LN14 in Figure 7. In this case, if the injection amount is controlled according to the actual intake manifold pressure, the air-fuel ratio changes as shown in LN15 in Figure 7. In contrast, the predicted value of the intake manifold pressure after a predetermined time changes so that the change begins at an earlier timing than LN14 in Figure 7, as shown in LN13 in Figure 7. Therefore, if the injection amount (LN11 in Figure 7) is controlled according to the predicted value of the intake manifold pressure, the change in the air-fuel ratio toward the lean side is suppressed compared to LN15 in Figure 7, as shown in LN16 in Figure 7.

[0078] As the system is repeatedly operated under these conditions, the injection amount is increased to maintain a constant air-fuel ratio, as shown in LN17 of Figure 7, and the predicted intake manifold pressure is also increased. For example, the injection amount and the predicted intake manifold pressure are adjusted so that the difference between the air-fuel ratio and the target air-fuel ratio is below a threshold, or the difference between the average air-fuel ratio over a predetermined period and the target air-fuel ratio is below a threshold. The adjusted injection amount is then set as the corrected injection amount, as shown in LN10 of Figure 7, and the adjusted predicted intake manifold pressure is set as the corrected predicted intake manifold pressure, as shown in LN12 of Figure 7 (S104). The difference in injection amount before and after correction is set as the correction value for the injection amount, and the difference in predicted intake manifold pressure before and after correction is set as the correction value for the predicted intake manifold pressure. When data has been acquired for all operating conditions (YES in S108), the function f(n) is set using the acquired data (S110). In other words, the coefficients a, b and the constant c of a linear function with the first injection amount and the Δ injection amount as parameters are calculated using the acquired data. As described above, the calculated function f(n) is compared and verified with the actual data, and if the correlation coefficient is within a predetermined range, it can be implemented in the control device 100 as a function for calculating the correction value C(n).

[0079] In this embodiment, the correction value for the predicted intake manifold pressure is calculated for each operating condition and stored in the memory of the control device 100 in association with the operating condition. In this way, for example, when the engine system 1 is in operation, the control device 100 corrects the predicted intake manifold pressure using the correction value stored in memory, sets the injection amount using the corrected predicted value, corrects the set injection amount using a correction value C(n) calculated using the function f(n), and controls the injection device so that the injection amount becomes the corrected amount.

[0080] Furthermore, the above explanation used Figure 7 as an example to illustrate how to calculate the injection quantity correction value and the predicted intake manifold pressure correction value to maintain the air-fuel ratio at the target air-fuel ratio under transient driving conditions such as acceleration. However, the same applies when calculating the injection quantity correction value and the predicted intake manifold pressure correction value under transient driving conditions such as deceleration. Therefore, a detailed explanation will not be repeated.

[0081] As described above, the engine system 1 according to this embodiment can suppress excess or deficiency in the injection amount and reduce deviations in the air-fuel ratio even during transient operation by correcting the amount of fuel that becomes excessive or insufficient when some of the gaseous fuel flows into other intake passages when the gaseous fuel is injected from the injector. Therefore, it is possible to provide an engine system that appropriately corrects the amount of gaseous fuel injected.

[0082] Furthermore, a correction value C(n) corresponding to the amount of gaseous fuel leaking into other intake passages is calculated using a function f(n) that shows the correlation between the first injection amount and the Δ injection amount in the current intake stroke. Therefore, the injection amount can be appropriately corrected even during transient periods when the operating conditions change.

[0083] Furthermore, since the correction value C(n) is calculated using a function f(n) that employs a linear equation, etc., it is possible to suppress increases in computational load and memory capacity when implementing it in the control device 100.

[0084] The following describes variations. In the above-described embodiment, we explained as an example the case where one function f(n) is set to calculate the correction value C(n) during transients. However, for example, different functions may be set for acceleration and deceleration. In this way, the correction value of the injection amount can be calculated with high accuracy for both acceleration and deceleration, so that the transient air-fuel ratio can be maintained at the target air-fuel ratio during both acceleration and deceleration.

[0085] Furthermore, in the above-described embodiment, the correction value for the predicted intake manifold pressure was explained as being stored for each operating condition as an example. However, for example, a function may be set up to calculate the correction value for the predicted intake manifold pressure using the predicted intake manifold pressure for the current intake stroke and the difference between the predicted intake manifold pressure for the current stroke and the predicted intake manifold pressure for the previous stroke as parameters. The method for setting the function is the same as the method for setting the coefficients a, b and the constant c of the function f(n) for calculating the injection amount correction value shown by the linear equation above, so a detailed explanation will not be repeated. In this way, it becomes unnecessary to store a large amount of data in memory, and the increase in computational load when implemented in the control device 100 can be suppressed. Furthermore, by correcting using the correlation between the predicted intake manifold pressure for the current stroke and the difference described above, the predicted intake manifold pressure can be obtained with high accuracy. This makes it possible to suppress deviations in the air-fuel ratio even during transient operation.

[0086] Furthermore, in the above-described embodiment, the case in which the injection amount is set using a predicted value of the intake manifold pressure was explained as an example, but the injection amount may also be set using a predicted value of the intake air volume or load factor instead of the intake manifold pressure. The control device 100 may calculate a predicted value of the intake air volume (or load factor) using the value detected from the intake air volume sensor 106 and the opening degree of the throttle valve 20, etc. In this case, the control device 100 may also calculate a correction value for the predicted intake air volume using a function whose parameters are the predicted intake air volume for the current intake stroke and the difference between the predicted intake air volume for the current stroke and the predicted intake air volume for the previous stroke. The method for setting the function is the same as the method for setting the coefficients a, b and the constant c of the function f(n) for calculating the correction value of the injection amount shown by the linear equation above, so a detailed explanation will not be repeated.

[0087] Furthermore, in the above embodiment, the case in which the correction value C(n) is calculated using a function f(n) with the first injection amount and Δ injection amount as parameters was explained as an example. However, it is also possible to set a function f(n) that uses at least one of the following as parameters in addition to the first injection amount and Δ injection amount: injection timing, the cylinder to be injected, and engine speed. In this case, especially when variations occur in the amount of fuel circulating between cylinders due to differences in engine speed, injection timing, and the cylinder to be injected, even with the same injection amount, the injection amount can be corrected with high accuracy by setting a function with parameters for injection amount and Δ injection amount.

[0088] Furthermore, if, after setting the function f(n), the correlation coefficient does not change, or changes only slightly, when any of the added parameters are omitted, then that parameter can be omitted. This helps to suppress the increase in computational load when implemented in the control device 100.

[0089] Furthermore, the modifications described above may be implemented in whole or in part. The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0090] 1 Engine system, 2 Engine block, 4 Intake manifold, 4a, 4b, 4c, 4d Branch passages, 4e Surge tank, 6 Intake pipe, 15, 16, 17, 18 Injector, 20 Throttle valve, 21, 22, 23, 24 Cylinder, 25, 26, 27, 28 Intake valve, 31, 32, 33, 34 Intake port, 35, 36, 37, 38 Exhaust valve, 100 Control device, 102 Intake pressure sensor, 104 Crank angle sensor, 106 Intake air volume sensor.

Claims

1. Multiple intake passages connected to each of the multiple cylinders, Multiple injection devices for injecting gaseous fuel into each of the multiple intake passages, The system includes a control device that controls the plurality of injection devices, The control device corrects the amount of gaseous fuel injected into one of the plurality of intake passages by the amount of fuel that is in excess or insufficient due to the injected gaseous fuel flowing into other intake passages. The control device calculates a first injection amount required in the first cylinder which is in the intake stroke, and the difference between the first injection amount and the second injection amount required in the second cylinder which is in the most recent intake stroke before the first cylinder. The control device then calculates a correction value using the correlation between the first injection amount, the difference, and a correction value for the injection amount that corresponds to the amount of fuel that is in excess or insufficient due to flowing into the other intake passages.

2. The control device is When performing synchronous injection during the intake stroke of each cylinder, a basic value for the injection amount is calculated to achieve the target air-fuel ratio. The difference is calculated using the previous base value, the second injection amount, and the current base value, the first injection amount. The correction value is calculated based on the first injection amount, the difference, and the correlation. The engine system according to claim 1, wherein the first injection amount is corrected by the correction value, and the synchronous injection is performed.

3. A plurality of intake passages connected to each of the plurality of cylinders, Multiple injection devices for injecting gaseous fuel into each of the multiple intake passages, The system includes a control device that controls the plurality of injection devices, The control device corrects the amount of gaseous fuel injected into one of the plurality of intake passages by the amount of fuel that is in excess or insufficient due to the injected gaseous fuel flowing into other intake passages. The control device is When performing synchronous injection during the intake stroke of each cylinder, the fluctuation of the intake manifold pressure in the intake passage is predicted based on the throttle opening, and a predicted value of the intake manifold pressure is calculated. The pressure difference between the previous predicted value and the current predicted value is calculated. Based on the predicted value and the pressure difference, a pressure correction value is calculated. An engine system that corrects the predicted value using the pressure correction value, calculates the injection amount based on the corrected predicted value, and performs the synchronous injection.

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