Fuel injection system

Abstract

To appropriately strengthen a tumble flow while suppressing a backflow of intake air.SOLUTION: A fuel injection system includes: intake valves 40a, 40b each having a valve head 42 and a valve stem 43 and opened to take in intake air from an intake port 20 into a cylinder part 12; an upstream side injector 52 disposed in the intake port 20 and injecting fuel toward a central direction of the intake valves 40a, 40b; and a downstream side injector 51 disposed downstream of the upstream side injector 52 in the intake port 20 and injecting fuel toward a direction of the valve stem 43 side of the valve head 42. The upstream side injector 52 injects the fuel in a compression stroke of an engine 10 before the intake valves 40a, 40b are closed. Due to this, while a backflow of the intake air is suppressed, a tumble flow can be strengthened appropriately.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a fuel injection system. [Background technology]

[0002] Conventionally, injectors that inject fuel by opening a valve have been used to supply fuel to an engine. Patent Document 1 discloses an engine in which a total of two injectors are installed above and below each intake port that communicates with a cylinder. In the engine of Patent Document 1, the upper injector is arranged with a nozzle at the tip facing diagonally downward, and the lower injector is arranged with a nozzle at the tip facing horizontally. The upper injector injects fuel during the intake stroke when the intake valve is open. On the other hand, the lower injector injects fuel during the exhaust stroke when the intake valve is closed, so that the fuel hits the valve body of the intake valve and is heated and vaporized. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-49398 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the engine of Patent Document 1, it is difficult to generate a tumble flow even if fuel is injected from the lower injector during the exhaust stroke. Also, intake air may flow back when the intake valve is open during the compression stroke, but the engine of Patent Document 1 does not disclose a method for preventing intake air from flowing back. In particular, when the engine load factor is high, the backflow becomes significant and the intake efficiency decreases, so some kind of measure is required.

[0005] The present invention has been made in consideration of the above-mentioned problems, and has an object to appropriately strengthen the tumble flow while suppressing the backflow of intake air. [Means for solving the problem]

[0006] The present invention is a fuel injection system for an engine comprising: an intake valve having a valve head and a valve stem, and opening to take in intake air from an intake port into a cylinder portion; an upstream injector disposed in the intake port and injecting fuel toward the center of the intake valve; and a downstream injector disposed in the intake port downstream of the upstream injector and injecting fuel in a direction toward the valve stem rather than the valve head, wherein the upstream injector injects fuel during the compression stroke of the engine and before the intake valve closes. Effect of the Invention

[0007] According to the present invention, it is possible to appropriately strengthen the tumble flow while suppressing the backflow of intake air. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a diagram illustrating an example of a configuration of a portion of an engine. [Diagram 2] FIG. 2 is a visualization of the intake air flow in a cylinder section. [Diagram 3] 2 is a diagram for explaining an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. FIG. [Figure 4] FIG. 4 is a diagram for explaining a period during which the upstream injector injects fuel. [Diagram 5] FIG. 1 is a diagram illustrating an example of a configuration of a fuel injection system. [Figure 6] 4 is a flowchart showing a process performed by a control device of the fuel injection system. [Figure 7] FIG. 4 is a diagram for explaining an injector to be used depending on an engine load factor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The embodiment according to the present invention includes intake valves 40a, 40b having a valve head 42 and a valve stem 43, and taking in intake air from the intake port 20 into the cylinder section 12 by opening the valves, an upstream injector 52 arranged in the intake port 20 and injecting fuel toward the center of the intake valves 40a, 40b, and a downstream injector 51 arranged in the intake port 20 downstream of the upstream injector 52 and injecting fuel toward the valve stem 43 side from the valve head 42. The upstream injector 52 injects fuel during the compression stroke of the engine 10 and before the intake valves 40a, 40b are closed. Therefore, it is possible to appropriately strengthen the tumble flow while suppressing the backflow of the intake air. EXAMPLES

[0010] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram showing an example of a configuration of a part of an engine 10 mounted on a vehicle according to an embodiment. FIG. 1(a) is a diagram showing the engine 10 as viewed from a direction perpendicular to the cylinder axis Cy (as viewed along the crankshaft Cr). FIG. 1(b) is a diagram showing the engine 10 as viewed along the cylinder axis Cy in the direction of arrow I shown in FIG. 1(a) (as viewed from a direction perpendicular to the crankshaft Cr). For ease of explanation, the side of the engine 10 on which the intake valve and the exhaust valve are arranged in the direction along the cylinder axis Cy is referred to as the top, the side of the intake valve and the exhaust valve on which the intake valve is arranged is referred to as the front, and one side in the direction along the crankshaft Cr is referred to as the left. However, the engine 10 is not limited to being mounted so that the cylinder axis Cy is aligned vertically with respect to the vehicle, and may be mounted so that the cylinder axis Cy is aligned horizontally, or may be mounted in a direction inclined in either the vertical or horizontal direction.

[0011] The engine 10 is a drive source for the vehicle, and is a four-stroke engine that performs a series of four strokes consisting of an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. The engine 10 of this embodiment has multiple cylinders and uses CNG (compressed natural gas) as the fuel to be burned in the combustion stroke. The engine 10 includes a cylinder block 11 and a cylinder head 14 .

[0012] The cylinder block 11 is integrally formed of a crankcase that rotatably supports the crankshaft and a cylinder section 12. A piston 13 is disposed inside the cylinder section 12 so as to be capable of reciprocating along a cylinder axis Cy. Here, the cylinder axis Cy refers to the central axis of the cylinder section 12. In Figs. 1(a) and 1(b), the cylinder axis Cy is indicated by a dashed line. The piston 13 and the crankshaft are connected via a connecting rod, and the reciprocating motion of the piston 13 causes the crankshaft to rotate around the crankshaft Cr via the connecting rod. The crankshaft axis Cr refers to the central axis of the crankshaft. In Fig. 1(b), the crankshaft axis Cr is indicated by a dashed line.

[0013] The cylinder head 14 is connected to the upper end of the cylinder block 11. A combustion chamber 15 is formed inside the cylinder head 14 by connecting the cylinder head 14 to the cylinder block 11. An ignition plug 16 is disposed in the cylinder head 14 with its tip located within the combustion chamber 15.

[0014] Further, the cylinder head 14 is formed with an intake port 20 that communicates with the inside of the cylinder section 12 (combustion chamber 15). The intake port 20 guides the intake air taken in via the intake pipe into the cylinder section 12. As shown in FIG. 1(a), the intake port 20 extends toward the combustion chamber 15 from the diagonally upper front side of the combustion chamber 15. As shown in FIG. 1(b), the intake port 20 of this embodiment has an intake inlet section 21 that serves as an intake for the intake, a first intake outlet section 22a and a second intake outlet section 22b that serve as outlets for the intake on the combustion chamber 15 side, and an intake passage section 23. The first intake outlet section 22a and the second intake outlet section 22b open at positions biased toward the front side of the combustion chamber 15, separated from each other in the left-right direction. The intake passage section 23 has a main intake passage 24, a first branch intake passage 26a that branches off from the main intake passage 24 to the right via a branch section, and a second branch intake passage 26b that branches off from the main intake passage 24 to the left via a branch section. The main intake passage 24 is a passage that communicates with the intake inlet section 21. Meanwhile, the first branch intake passage 26a is a passage that communicates with the first intake outlet section 22a, and the second branch intake passage 26b is a passage that communicates with the second intake outlet section 22b. The first branch intake passage 26a and the second branch intake passage 26b extend approximately parallel to each other and are spaced apart in the left-right direction.

[0015] Further, the cylinder head 14 is formed with an exhaust port 30 that communicates with the inside of the cylinder section 12 (combustion chamber 15). The exhaust port 30 guides exhaust gas burned in the combustion chamber 15 to an exhaust pipe. The exhaust port 30 extends from the combustion chamber 15 diagonally upward toward the rear and curves toward one side in the left-right direction (the right side in this case). As shown in FIG. 1(b), the exhaust port 30 of this embodiment has a first exhaust inlet section 31a and a second exhaust inlet section 31b that serve as an inlet for exhaust gas, an exhaust outlet section 32 that serves as an outlet for exhaust, and an exhaust passage section 33. The first exhaust inlet section 31a and the second exhaust inlet section 31b open at positions biased toward the rear side of the combustion chamber 15 and separated from each other in the left-right direction. The exhaust passage section 33 has a first branch exhaust passage 34a communicating with the first exhaust inlet section 31a, a second branch exhaust passage 34b communicating with the second exhaust inlet section 31b, and a main exhaust passage 36 in which the first branch exhaust passage 34a and the second branch exhaust passage 34b join together via a joining section. The first branch exhaust passage 34a and the second branch exhaust passage 34b extend generally parallel to each other and are spaced apart in the left-right direction. On the other hand, the main exhaust passage 36 is a passage that communicates with the exhaust outlet section 32.

[0016] An intake valve is provided in the intake port 20 to take in intake air from the intake port 20 into the cylinder section 12 (combustion chamber 15) when the intake valve is opened. On the other hand, an exhaust valve is provided in the exhaust port 30 to discharge exhaust gas from the cylinder section 12 to the exhaust port 30 when the exhaust valve is opened. The cylinder head 14 of this embodiment has an intake valve 40a corresponding to the first intake outlet portion 22a and an intake valve 40b corresponding to the second intake outlet portion 22b. The cylinder head 14 of this embodiment also has an exhaust valve 41a corresponding to the first exhaust inlet portion 31a and an exhaust valve 41b corresponding to the second exhaust inlet portion 31b. The intake valves 40a, 40b and the exhaust valves 41a, 41b of this embodiment are arranged so that the included angle α is approximately 20° to 40°, more specifically, approximately 25° to 35°.

[0017] The intake valves 40a, 40b and the exhaust valves 41a, 41b each have an umbrella-shaped valve head 42 and an axial valve stem 43. The intake valves 40a, 40b and the exhaust valves 41a, 41b are arranged such that the valve heads 42 are located on the combustion chamber 15 side and the valve stems 43 are located away from the combustion chamber 15. The intake valves 40a, 40b and the exhaust valves 41a, 41b are capable of sliding along the axial direction of the valve stem 43 as the valve stem 43 is guided by the cylinder head 14. The intake valves 40a, 40b and the exhaust valves 41a, 41b are constantly biased in a direction in which the valve head 42 abuts against the first intake outlet 22a, the second intake outlet 22b, the first exhaust inlet 31a, and the second exhaust inlet 31b, respectively, by valve springs arranged to surround the respective valve stems 43. When the valve head 42 abuts against the first intake outlet 22a, the second intake outlet 22b, the first exhaust inlet 31a, and the second exhaust inlet 31b, respectively, the intake valves 40a, 40b and the exhaust valves 41a, 41b are closed.

[0018] Meanwhile, the intake valves 40a, 40b and the exhaust valves 41a, 41b are pressed against the bias of the valve springs by the intake cam and exhaust cam rotatably supported by the cylinder head 14. The intake valves 40a, 40b and the exhaust valves 41a, 41b are temporarily separated from the first intake outlet 22a, the second intake outlet 22b, the first exhaust inlet 31a, and the second exhaust inlet 31b as the valve head 42 slides toward the center of the cylinder section 12. As the valve head 42 moves away from the first intake outlet 22a, the second intake outlet 22b, the first exhaust inlet 31a, and the second exhaust inlet 31b, respectively, the intake valves 40a, 40b and the exhaust valves 41a, 41b open. FIG. 1(a) shows a state in which the intake valves 40a, 40b are open and the exhaust valves 41b, 41b are closed.

[0019] The intake cam and exhaust cam are connected to the crankshaft via a cam chain and rotate in conjunction with the rotation of the crankshaft. The intake cam and exhaust cam control the opening and closing timing of intake valves 40a, 40b and exhaust valves 41a, 41b during the intake stroke, compression stroke, combustion stroke, and exhaust stroke of engine 10.

[0020] The engine 10 also includes a downstream injector 51 and an upstream injector 52 . First, the downstream injector 51 will be described. The downstream injector 51 is axially shaped and injects fuel from its tip. The downstream injector 51 is disposed in the cylinder head 14 and is located in the intake port 20 downstream of the upstream injector 52. Specifically, the downstream injector 51 is located close to the branching portion of the intake port 20 and is located such that an injection port is exposed from the lower surface of the inner circumferential surface of the intake passage portion 23. Further, the downstream injector 51 of this embodiment has two injection ports spaced apart in the left-right direction. Of the two injection ports, the injection port on one side in the left-right direction (here, the right side) is set so that the fuel is directed toward the intake valve 40a, i.e., toward the first intake outlet 22a. On the other hand, the injection port on the other side in the left-right direction (here, the left side) is set so that the fuel is directed toward the intake valve 40b, i.e., toward the second intake outlet 22b.

[0021] The downstream injector 51 is positioned and its injection direction is set so as to mainly strengthen the tumble flow. Here, the tumble flow is a vortex air flow generated in the cylinder section 12, and refers to a flow whose rotation axis is perpendicular to the cylinder axis Cy. By generating the tumble flow, it is possible to promote mixing of the intake air and the fuel in the cylinder section 12. First, downstream injector 51 is set so that the fuel injection direction is at an angle close to horizontal (an angle close to parallel to the top surface of piston 13). To achieve this, downstream injector 51 is disposed so that the axis of the injector body is at an angle closer to horizontal than the axis of the injector body of upstream injector 52. Downstream injector 51 injects fuel from the injection port so that it spreads in a cone shape. Here, the center of the cone (see two-dot chain line A1) is set to be the direction of fuel injection by downstream injector 51.

[0022] As shown in FIG. 1(a), the direction of fuel injection by the downstream injector 51 is set to pass above the valve head 42 (on the valve stem 43 side) of the open intake valves 40a and 40b. Therefore, the fuel injected by the downstream injector 51 flows into the cylinder section 12 through between the first intake outlet 22a and the valve head 42 and between the second intake outlet 22b and the valve head 42. The direction of fuel injection by the downstream injector 51 is set to pass below the valve head 42 of the exhaust valves 41a and 41b. Here, the direction of fuel injection by the downstream injector 51 is set to be parallel to the surface (lower surface) of the valve head 42 of the exhaust valves 41a and 41b that faces the cylinder section 12. When a concave curved surface is formed on the surface of the valve head 42 facing the cylinder portion 12, the direction of fuel injection by the downstream injector 51 is parallel to the flat surface other than the curved surface. In other words, the direction of fuel injection by the downstream injector 51 is set to be perpendicular to the axial direction of the valve stems 43 of the exhaust valves 41a, 41b.

[0023] 1(b), the direction of fuel injection by the downstream injector 51 is set toward the left or right side of the valve stem 43 so as to avoid the injected fuel hitting the valve stem 43 of the intake valves 40a, 40b. Specifically, the direction of fuel injection from the downstream injector 51 toward the intake valve 40a is set toward the left side of the valve stem 43 of the intake valve 40a, and the direction of fuel injection from the downstream injector 51 toward the intake valve 40b is set toward the right side of the valve stem 43 of the intake valve 40b. Therefore, the fuel injected by the downstream injector 51 flows into the cylinder section 12 through between the first intake outlet 22a and the valve head 42 and between the second intake outlet 22b and the valve head 42 without interfering with the valve stem 43.

[0024] Fig. 2 is a visualization diagram of the intake air flow in the cylinder section 12 when fuel is injected from the downstream injector 51. In Fig. 2, the direction in which the intake air flows is indicated by short arrows, and the thicker the arrows are, the faster the flow speed is. The fuel injected from the downstream injector 51 avoids the valve head 42 of the open intake valves 40a, 40b and passes above the valve head 42 toward the cylinder section 12. Therefore, as shown in FIG. 2, the intake air that flows in together with the injected fuel in the cylinder section 12 hits the rear bore surface of the cylinder section 12 and flows toward the piston 13. The intake air that flows toward the piston 13 flows forward along the top surface of the piston 13, hits the front bore surface of the cylinder section 12, and flows toward the intake valves 40a, 40b. Therefore, a tumble flow indicated by the long thick arrow can be generated. Here, as described above, the direction of fuel injection by the downstream injector 51 is set to pass above the valve head 42 of the open intake valves 40a, 40b and be parallel to the lower surface of the valve head 42 of the exhaust valves 41a, 41b. Therefore, the intake air flowing in together with the fuel flows at a high flow rate within the cylinder portion 12, thereby strengthening the tumble flow.

[0025] Next, the upstream injector 52 will be described. The upstream injector 52 is axially shaped and injects fuel from its tip. The upstream injector 52 is disposed in the cylinder head 14, and is located in the intake port 20 upstream of the downstream injector 51. Specifically, the upstream injector 52 is disposed in the main intake passage 24 or a branching portion of the intake port 20, and is positioned so that an injection port is exposed from the upper surface of the inner circumferential surface of the intake passage portion 23. Furthermore, the upstream injector 52 of this embodiment has two injection ports spaced apart in the left-right direction. Of the two injection ports, the injection port on one side in the left-right direction (here, the right side) is set so that the fuel is directed toward the intake valve 40a, i.e., toward the first intake outlet 22a. On the other hand, the injection port on the other side in the left-right direction (here, the left side) is set so that the fuel is directed toward the intake valve 40b, i.e., toward the second intake outlet 22b.

[0026] The upstream injector 52 is positioned, and its injection direction and injection timing are set so as to mainly suppress the backflow of intake air. First, the upstream injector 52 is set so that the fuel injection direction is toward the cylinder section 12. The upstream injector 52 is also set so that the fuel injection direction is along the intake passage section 23 of the intake port 20. For this reason, the upstream injector 52 is disposed so that the axis of the injector body forms an angle (angle along the cylinder axis Cy) closer to the vertical than the axis of the injector body of the downstream injector 51. The upstream injector 52 injects fuel from the injection port so that it spreads in a cone shape. Here, the center of the cone (see the two-dot chain line A2) is set to be the injection direction of fuel by the upstream injector 52.

[0027] As shown in Fig. 1(a), the direction of fuel injection by the upstream injector 52 is set to be toward the valve head 42 of the open intake valves 40a, 40b. Specifically, the direction of fuel injection by the upstream injector 52 is set toward the center of the valve head 42 of the open intake valves 40a, 40b. Also, as shown in Fig. 1(b), the direction of fuel injection by the upstream injector 52 is set to be toward the valve stem 43 of the intake valves 40a, 40b. Therefore, the fuel injected by the upstream injector 52 is directed toward the cylinder portion 12.

[0028] Furthermore, the timing of fuel injection by the upstream injector 52 is set to occur during the compression stroke of the engine 10 and before the intake valves 40a, 40b close. Here, the opening and closing timing of the intake valves 40a, 40b and the exhaust valves 41a, 41b during the intake stroke, compression stroke, combustion stroke, and exhaust stroke of the engine 10 will be briefly described.

[0029] Fig. 3(a) is a schematic diagram showing the state of the engine 10 during the intake stroke, compression stroke, combustion stroke, and exhaust stroke. Fig. 3(b) is a diagram showing the valve lift amount of the intake valves 40a, 40b and the valve lift amount of the exhaust valves 41a, 41b during the intake stroke, compression stroke, combustion stroke, and exhaust stroke. In Fig. 3(b), the horizontal axis represents the crank angle, and the vertical axis represents the valve lift amount.

[0030] During the intake stroke, the piston 13 descends from the top dead center to the bottom dead center. The exhaust valves 41a and 41b are closed immediately after the intake stroke is started by the exhaust cam. Meanwhile, the intake valves 40a and 40b are opened during the intake stroke by the intake cam. The intake valves 40a and 40b are opened immediately before the exhaust stroke ends and closed immediately after the compression stroke starts. During the intake stroke, the piston 13 descends from the top dead center to the bottom dead center, creating a negative pressure inside the cylinder section 12. Therefore, by injecting fuel during the intake stroke, the intake air mixed with the fuel flows into the cylinder section 12.

[0031] During the compression stroke, the piston 13 rises from the bottom dead center to the top dead center. The exhaust valves 41a, 41b are closed during the compression stroke by the exhaust cam, and the intake valves 40a, 40b are also closed almost during the compression stroke, so that the mixture that flows into the cylinder section 12 during the intake stroke is compressed. As described above, the intake valves 40a, 40b close immediately after the start of the compression stroke. That is, there is a period during which the intake valves 40a, 40b are open immediately after the start of the compression stroke.

[0032] During the combustion stroke, the compressed air-fuel mixture is ignited by the spark plug 16 and combusted, pushing the piston 13 down from top dead center to bottom dead center. The exhaust valves 41a, 41b are opened by the exhaust cam just before the end of the combustion stroke. Meanwhile, the intake valves 40a, 40b are closed by the intake cam during the combustion stroke. The crankshaft rotates during the combustion stroke.

[0033] During the exhaust stroke, the piston 13 rises from the bottom dead center to the top dead center. The exhaust valves 41a, 41b are opened during the exhaust stroke by the exhaust cam. On the other hand, the intake valves 40a, 40b are almost closed during the exhaust stroke, so that the exhaust gas generated during the combustion stroke is discharged from the cylinder section 12. At the boundary between the exhaust stroke and the intake stroke, there is an overlap period during which both the intake valves 40a, 40b and the exhaust valves 41a, 41b are open.

[0034] In this manner, engine 10 repeats four cycles, namely, intake stroke, compression stroke, combustion stroke, and exhaust stroke, so that driving force is transmitted from engine 10 via the crankshaft to the drive wheels, causing the vehicle to run. During the compression stroke described above, the intake valves 40a, 40b close immediately after the start of the compression stroke, so that some of the intake air mixed with fuel may be pushed back by the piston 13 rising from the bottom dead center to the top dead center and may flow back into the intake port 20.

[0035] Fig. 4 is a diagram showing the valve lift amount of the intake valves 40a, 40b centered on the intake stroke, and the intake air amount (intake air flow rate) of the intake air taken into the cylinder portion 12. Fig. 4 is also a diagram for explaining the period during which the upstream injector 52 injects fuel. In Fig. 4, the horizontal axis represents the crank angle, and the vertical axis represents the valve lift amount of the intake valve or the intake air amount.

[0036] As shown in Figure 4, during the intake stroke, the piston 13 descends from the top dead center and the intake valves 40a, 40b open, increasing the amount of intake air drawn into the cylinder section 12. Thereafter, as the piston 13 approaches the bottom dead center, the amount of intake air drawn into the cylinder section 12 decreases. Furthermore, as the intake stroke transitions to the compression stroke, the piston 13 rises from the bottom dead center, causing the intake air to be pushed back and flow backwards.

[0037] In order to suppress such backflow of intake air, the upstream injector 52 injects fuel during the compression stroke before the intake valves 40a, 40b close. In FIG. 4, the period during which the upstream injector 52 injects fuel is indicated by an outlined arrow. Specifically, the upstream injector 52 starts injecting fuel during the compression stroke and ends the injection of fuel when the intake valves 40a, 40b close. In this way, by the upstream injector 52 injecting fuel during the compression stroke before the intake valves 40a, 40b close, the intake air that flows back can be pushed back to the opposite side, i.e., the cylinder portion 12 side, thereby suppressing the backflow of intake air. The timing when the upstream injector 52 starts injecting fuel is not limited to being simultaneous or approximately simultaneous with the compression stroke, but may be during the compression stroke and before the intake valves 40a, 40b close. The timing when the upstream injector 52 stops injecting fuel is not limited to being simultaneous or approximately simultaneous with the closing of the intake valves 40a, 40b, but may be during the compression stroke and before the intake valves 40a, 40b close.

[0038] In particular, the higher the engine load factor, the more pronounced the backflow of intake air is. Therefore, when the backflow of intake air becomes significant, the upstream injector 52 can inject fuel during the compression stroke and before the intake valves 40a, 40b close. Conversely, when the backflow of intake air is not significant, the upstream injector 52 does not inject fuel.

[0039] On the other hand, the downstream injector 51 always injects fuel regardless of the engine load factor. The downstream injector 51 injects fuel during at least a part of the intake stroke and the compression stroke and before the intake valves 40a, 40b are closed. Specifically, the downstream injector 51 injects fuel during the period from when the intake valves 40a, 40b are opened to when they are closed, thereby injecting the fuel into the cylinder portion 12, thereby appropriately strengthening the tumble flow. In particular, the timing for ending the fuel injection of the downstream injector 51 is set to be simultaneous or approximately simultaneous with the closing of the intake valves 40a, 40b, thereby further strengthening the tumble flow.

[0040] The downstream injector 51 and the upstream injector 52 complement each other's shortcomings. That is, the downstream injector 51 can strengthen the tumble flow, but cannot direct the flow in the intake port 20 in a direction along the intake passage 23 because it is disposed close to the intake valves 40a, 40b in order to strengthen the tumble flow. On the other hand, the upstream injector 52 can direct the flow in the intake port 20 in a direction along the intake passage 23 in order to suppress the backflow of intake air, but cannot strengthen the tumble flow. In this way, the downstream injector 51 and the upstream injector 52 can complement each other's shortcomings.

[0041] Next, a configuration of a fuel injection system for an engine that realizes the method of injecting fuel by downstream injector 51 and upstream injector 52 as described above will be described. FIG. 5 is a diagram showing an example of the configuration of a fuel injection system. The fuel injection system includes an engine 10, a control device 50, a detection unit 60, and the like. As described above, the engine 10 has the downstream injector 51, the upstream injector 52, and the like.

[0042] The control device 50 controls the engine 10. The control device 50 may also function as a control device that controls the vehicle, or may be a device different from the control device that controls the vehicle. In addition, the control device 50 may be configured, for example, by one ECU (Electronic Control Unit), or may be configured by multiple ECUs working together. The control device 50 controls the downstream injector 51 and the upstream injector 52 based on the information detected by the detection unit 60 .

[0043] The detection unit 60 detects various states of the vehicle or the engine 10. Specifically, the detection unit 60 has a throttle position sensor 61, an engine speed sensor 62, a crank angle sensor 63, an airflow sensor 64, and the like. The throttle position sensor 61 detects information on the throttle angle of a throttle valve disposed in an intake pipe. The control device 50 receives the information on the throttle angle detected by the throttle position sensor 61. The engine speed sensor 62 detects the engine speed, specifically, the number of revolutions per unit time of the crankshaft. The control device 50 receives the information on the engine speed detected by the engine speed sensor 62. The crank angle sensor 63 detects information on the crank angle (the rotation angle of the crankshaft). The control device 50 receives the information on the crank angle detected by the crank angle sensor 63. The airflow sensor 64 detects information on the amount of intake air. The control device 50 receives the information on the amount of intake air detected by the airflow sensor 64.

[0044] Next, the process executed by the control device 50 of the fuel injection system according to this embodiment will be described with reference to the flowchart of Fig. 6. The flowchart of Fig. 6 is realized, for example, by a CPU included in the ECU of the control device 50 executing a program stored in a memory. The flowchart of Fig. 6 is started by driving the engine 10, and is executed while the engine 10 is driving.

[0045] In S10, the control device 50 acquires information on the current engine load factor. Here, the engine load factor is the ratio of the current intake air amount to the maximum intake air amount according to the engine speed. Maximum value data indicating the maximum intake air amount according to the engine speed is stored in advance in the memory of the control device 50. The control device 50 acquires information on the current engine speed from the engine speed sensor 62 and acquires information on the current intake air amount from the air flow sensor 64. The control device 50 acquires information on the maximum intake air amount according to the current engine speed by referring to the maximum value data. Next, the control device 50 acquires information on the current engine load factor by calculating the ratio of the current intake air amount to the maximum intake air amount according to the engine speed based on the acquired information on the maximum intake air amount and the current intake air amount. The engine load factor may be an accelerator opening detected by an accelerator opening sensor.

[0046] In S11, the control device 50 judges whether or not the current engine load factor is greater than a predetermined load factor. The predetermined load factor is a load factor at which the backflow of intake air becomes noticeable in the intake port 20 during the compression stroke. The predetermined load factor may be set by actually driving the engine 10 to measure the load factor at which the backflow of intake air becomes noticeable, or may be set by calculating the load factor at which the backflow of intake air becomes noticeable through a simulation. Information on the predetermined load factor is stored in the memory of the control device 50. The predetermined load factor is, for example, a value between 92% and 98%, and is approximately 95% in this embodiment. If the current engine load factor is not greater than the predetermined load factor, the process proceeds to S12, and if it is greater, the process proceeds to S14.

[0047] Here, the current engine load factor is compared with the predetermined load factor in order to determine which injector to use. Fig. 7 is a diagram for explaining whether to use an upstream injector or a downstream injector depending on the engine load factor. In Fig. 7, different injector combinations are selected when the current engine load factor is greater than a predetermined load factor (here, 95%) and when it is equal to or less than the predetermined load factor. Also, the injector combination to be used differs depending on the engine load factor, regardless of the engine speed. Specifically, when the current engine load rate is equal to or lower than a predetermined load rate, only the downstream injector 51 is used, and when the current engine load rate is greater than the predetermined load rate, both the downstream injector 51 and the upstream injector 52 are used.

[0048] Returning to the flowchart of FIG. 6, if the current engine load factor is not greater than the predetermined load factor, the process proceeds to S12. In S12, the control device 50 calculates the injection amount of the downstream injector 51 when injecting fuel only from the downstream injector 51. The reason for injecting fuel only from the downstream injector 51 is that the current engine load factor does not cause significant backflow of intake air, and therefore there is no need to suppress the backflow of intake air by injecting fuel from the upstream injector 52. The control device 50 calculates the injection amount based on information about the throttle angle detected by the throttle position sensor 61.

[0049] In S13, the control device 50 injects fuel only from the downstream injector 51 based on the calculated injection amount, and does not inject fuel from the upstream injector 52. In addition, the control device 50 injects fuel from the downstream injector 51 during at least a part of the intake stroke and the compression stroke, based on information about the crank angle detected by the crank angle sensor 63. In this way, the tumble flow can be strengthened by injecting fuel from the downstream injector 51. When the process of S13 ends, the process of the flowchart in FIG.

[0050] On the other hand, if the current engine load factor is greater than the predetermined load factor, the process proceeds to S14. In S14, the control device 50 calculates the injection amount of each injector when injecting fuel from the downstream injector 51 and the upstream injector 52. The reason for injecting fuel from both the downstream injector 51 and the upstream injector 52 is that the current engine load factor causes a significant backflow of intake air, and therefore fuel is injected from the upstream injector 52 to suppress the backflow of intake air. First, the control device 50 calculates the total injection amount based on the information of the throttle angle detected by the throttle position sensor 61. Next, the control device 50 calculates the injection amount required to suppress the backflow as the injection amount of fuel to be injected from the upstream injector 52 based on the engine load factor. Next, the control device 50 calculates the injection amount obtained by subtracting the injection amount required to suppress the backflow from the total injection amount as the injection amount of fuel to be injected from the downstream injector 51. The memory may previously store a table that associates the injection amount information of the downstream injector 51 and the injection amount information of the upstream injector 52 with the throttle angle information and the engine load factor information. The control device 50 can calculate the injection amount of the downstream injector 51 and the injection amount of the upstream injector 52 by referring to the table based on the acquired throttle angle information and engine load factor information.

[0051] In S15, the control device 50 injects fuel from the downstream injector 51 and the upstream injector 52 based on the calculated injection amount. Also, the control device 50 injects fuel from the upstream injector 52 during the compression stroke of the engine 10 and before the intake valves 40a, 40b are closed, based on information about the crank angle detected by the crank angle sensor 63. Also, the control device 50 injects fuel from the downstream injector 51 during at least a part of the intake stroke and the compression stroke, based on information about the crank angle detected by the crank angle sensor 63. When the process of S15 ends, the process of the flowchart in FIG. 6 ends.

[0052] As described above, according to this embodiment, the upstream injector 52 can push back the backflow of intake air toward the cylinder portion 12 by injecting fuel during the compression stroke of the engine 10 and before the intake valves 40a, 40b are closed, thereby suppressing the backflow of intake air. Furthermore, suppressing the backflow of intake air can improve the intake efficiency.

[0053] Furthermore, according to this embodiment, the upstream injector 52 injects fuel when the engine load rate is greater than a predetermined load rate. When the engine load rate is not greater than the predetermined load rate, the backflow of intake air is not significant, so fuel can be used efficiently by injecting fuel only from the downstream injector 51, which can strengthen the tumble flow. On the other hand, when the engine load rate is greater than the predetermined load rate, fuel can be appropriately strengthened while preventing the backflow of intake air by injecting fuel from the downstream injector 51 and the upstream injector 52.

[0054] Furthermore, according to this embodiment, the downstream injector 51 injects fuel in a direction that avoids the valve stem 43 of the intake valves 40a, 40b. Therefore, interference with the valve stem 43 can be suppressed, and a large tumble flow can be formed in the cylinder portion 12. In particular, since the upstream injector 52 plays a role in suppressing the backflow of intake air, the downstream injector 51 can focus on strengthening the tumble flow, and therefore the downstream injector 51 can inject fuel in a direction that avoids the valve stem 43.

[0055] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and modifications and the like are possible within the scope of the present invention.

[0056] In the present embodiment, the engine 10 has been described as being configured with two intake passages (first branch intake passage 26a, second branch intake passage 26b) and two exhaust passages (first branch exhaust passage 34a, second branch exhaust passage 34b) for each cylinder section 12, but is not limited to this. For example, there may be one intake passage for each cylinder section 12. Also, there may be one exhaust passage for each cylinder section 12.

[0057] In this embodiment, the downstream injector 51 and the upstream injector 52 are each capable of injecting fuel in two directions, but the present invention is not limited to this. For example, the downstream injector 51 and the upstream injector 52 may each inject fuel in one direction. In this case, the downstream injector 51 and the upstream injector 52 can be arranged for each intake passage (first branch intake passage 26a, second branch intake passage 26b). Also, for example, one of the downstream injector 51 and the upstream injector 52 may be configured to inject fuel in one direction, and the other may be configured to inject fuel in two directions. In this case, three injectors can be arranged in the intake port 20.

[0058] In the present embodiment, the engine 10 is described as having multiple cylinders, but the present invention is not limited to this, and may be a single cylinder. In addition, the present invention is described as using CNG (compressed natural gas) as the fuel to be burned in the combustion stroke, but the present invention is not limited to this, and may be other gaseous fuel or liquid fuel. [Explanation of symbols]

[0059] 10: Engine 12: Cylinder section 13: Piston 20: Intake port 40a, 40b: Intake valves 41a, 41b: Exhaust valves 42: Valve head 43: Valve stem 50: Control device 51: Downstream injector 52: Upstream injector

Claims

1. an intake valve having a valve head and a valve stem, and taking in intake air from an intake port into a cylinder portion by opening the valve; an upstream injector disposed in the intake port and configured to inject fuel toward a center of the intake valve; a downstream injector that is disposed in the intake port downstream of the upstream injector and injects fuel toward the valve stem side relative to the valve head, The upstream injector is 13. A fuel injection system comprising: a compressor for injecting fuel into a combustion chamber of the engine;

2. The upstream injector is 2. The fuel injection system according to claim 1, wherein fuel is injected when the engine load factor is greater than a predetermined load factor.

3. The downstream injector is 3. The fuel injection system according to claim 1, wherein fuel is injected in a direction that avoids the valve stem.

Images