internal combustion engine

Abstract

To provide a 2-valve internal combustion engine in which there is provided an ignition plug positioned on a lateral side in an air suction flow direction between an air suction valve port center and an air discharge valve port center, and which provides a stable lean combustion by suppressing disturbance in a tumble flow.SOLUTION: An internal combustion engine is provided, comprising: a single intake valve 46 and a single exhaust valve 50 that open and close a combustion chamber 20 composed of a cylinder head 14 and a top surface 15a of a piston 15; an intake valve port and an exhaust valve port 30; an intake port 32; a tumble aisle 64; and an ignition plug 21 arranged on a lateral side of the combustion chamber 20. A tumble flow enters orthogonally to a virtual line L between a center point C1 of the intake valve port 28 and a center point C2 of the exhaust valve port 30. A recess 102 is provided which is arranged on a combustion chamber ceiling surface 100 on a side of the cylinder head 14 and on an upstream side of the ignition plug 21 with respect to a flow-in direction of the tumble flow. A lean combustion is stabilized by suppressing disturbance in the tumble flow.SELECTED DRAWING: Figure 15

Description

[Technical Field]

[0001] The present invention relates to a two-valve internal combustion engine. [Background technology]

[0002] In recent years, research and development has been conducted to improve fuel efficiency and contribute to energy efficiency, in order to ensure that more people have access to affordable, reliable, sustainable and advanced energy.

[0003] Incidentally, in this technology relating to improvement of fuel efficiency, an internal combustion engine is disclosed that is a four-valve type, has a pent roof type combustion chamber, and has a recess on the pent roof surface of the cylinder head (see Patent Document 1).

[0004] In this pent roof type four-valve internal combustion engine, the spark plug is located near the top of the roof surface of the combustion chamber, and by forming a recess on the upstream side of the tumble flow that flows around the spark plug on this roof surface, the tumble flow that flows along this pent roof surface is concentrated and rectified in the recess, suppressing fluctuations in the flow of the tumble flow and, as a result, maintaining stability for lean combustion.

[0005] In this way, in a pent roof type four-valve internal combustion engine, by forming a recess on the ceiling surface of the combustion chamber upstream of the tumble flow that flows around the spark plug, a strong tumble flow can be generated in the intake to exhaust direction, thereby suppressing variation in the tumble flow.

[0006] On the other hand, in inexpensive two-valve internal combustion engines, the intake and exhaust valves are positioned in the direction of intake to exhaust flow at the center of the cylinder, and the spark plug is positioned on the side of the combustion chamber, which is located to the side of the intake flow direction connecting the center of the intake valve port and the center of the exhaust valve port.Therefore, the tumble flow generated in the intake flow direction connecting the center of the combustion chamber intake valve port and the center of the exhaust valve port is not sufficiently effective in suppressing turbulence in the intake flow flowing around the spark plug and in achieving stability for lean combustion. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication WO2019 / 197860 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made with this in mind, and aims to provide a two-valve internal combustion engine that can suppress turbulence of the tumble flow and stabilize lean combustion even when the spark plug is located to the side of the intake air flow direction connecting the intake valve port center and the exhaust valve port center, thereby contributing to improved energy efficiency. [Means for solving the problem]

[0009] The present invention has been made to solve the above-mentioned problems, and provides an engine having a combustion chamber formed by a cylinder head and a top surface of a piston, a single intake valve and a single exhaust valve for opening and closing the combustion chamber; an intake valve port that is opened and closed by the intake valve; and an exhaust valve port that is opened and closed by the exhaust valve. an intake port communicating with the intake valve port; a tumble passage disposed before the intake port; a spark plug disposed on the side of the combustion chamber; The tumble flow generated by the tumble passage flows obliquely with respect to an imaginary line connecting the center point of the intake valve port and the center point of the exhaust valve port, a combustion chamber ceiling surface on the cylinder head side of the combustion chamber has a recess; The internal combustion engine is characterized in that the recess is disposed upstream of the spark plug with respect to the inflow direction of the tumble flow.

[0010] According to the above configuration, it is possible to suppress turbulence of the intake air flow around the spark plug due to the tumble flow, thereby improving the stability of lean combustion.

[0011] In the above configuration, the top surface of the piston can preferably be formed into a concave shape.

[0012] According to the above configuration, by forming the top surface of the piston into a concave shape, it is possible to maintain the flow of the tumble flow for a longer period of time.

[0013] In the above configuration, the recess may preferably be continuous with an ignition plug hole into which the ignition plug is inserted.

[0014] According to the above configuration, no edge shape is generated around the spark plug, and the flow of tumble flow can be improved.

[0015] In the above configuration, preferably, the recess may be provided continuously from the outer periphery of the ceiling surface of the combustion chamber toward the spark plug hole.

[0016] According to the above configuration, the shape of the combustion chamber does not become complicated, making it easy to manufacture, and it is possible to simplify the manufacturing process and reduce manufacturing costs.

[0017] In the above-described configuration, preferably, the recess may have a width substantially equal to the width of the spark plug hole from the upstream side of the tumble flow and may be provided so as to be continuous with the spark plug hole.

[0018] According to this configuration, there is no change in the cross-sectional area of ​​the recess perpendicular to the direction of the tumble flow, and the tumble flow can be stably caused to flow.

[0019] In the above-described configuration, preferably, the recess has a uniform cross-sectional area perpendicular to the flow direction of the tumble flow that flows on the ceiling surface of the combustion chamber.

[0020] According to the above configuration, the cross-sectional area perpendicular to the flow direction of the tumble flow flowing along the ceiling surface of the combustion chamber in the recess is uniform, and therefore, the small change in cross-sectional area can further suppress turbulence of the intake flow flowing around the ignition plug.

[0021] In the above configuration, preferably, the center of gravity of the combustion chamber may be located closer to the intake valve port and closer to the spark plug hole into which the spark plug is inserted, relative to the direction of the imaginary line.

[0022] According to the above configuration, by positioning the volumetric center of gravity of the combustion chamber closer to the intake valve port and closer to the spark plug hole into which the spark plug is inserted in the direction of the imaginary line, it is possible to bring the high turbulence intensity region closer to the initial flame without increasing the average turbulence intensity of the intake air within the combustion chamber, thereby promoting stable flame growth even in lean conditions.

[0023] The present invention relates to a combustion chamber formed by a cylinder head and a top surface of a piston, a single intake valve and a single exhaust valve for opening and closing the combustion chamber; an intake valve port that is opened and closed by the intake valve; and an exhaust valve port that is opened and closed by the exhaust valve. an intake port communicating with the intake valve port; a tumble passage disposed before the intake port; a spark plug disposed on the side of the combustion chamber; a first intake passage for generating a tumble flow in the combustion chamber and a second intake passage are provided in an intake passage communicating with the combustion chamber so as to overlap with each other in the direction of the cylinder axis; the first intake passage is curved in the direction of the cylinder axis so as to move away from the second intake passage, and is curved in a width direction perpendicular to the cylinder axis and perpendicular to the intake / exhaust direction, a combustion chamber ceiling surface on the cylinder head side of the combustion chamber has a recess; The internal combustion engine is characterized in that the recess is disposed upstream of the spark plug with respect to the inflow direction of the tumble flow.

[0024] According to the above configuration, the first intake passage for generating a tumble flow in the combustion chamber is curved so as to move away from the second intake passage in the direction of the cylinder axis, and is curved in a width direction perpendicular to the cylinder axis and perpendicular to the intake / exhaust direction. By forming the first intake passage so as to move away from the second intake passage in the direction of the cylinder axis, the intake air from the first intake passage can flow smoothly into the combustion chamber so as to form a tumble flow, and in some cases it is possible to increase the flow velocity of the intake air from the first intake passage. Furthermore, by forming the first intake passage so as to be curved in the width direction perpendicular to the cylinder axis and perpendicular to the intake / exhaust direction, it is possible to reduce the degree to which the intake air from the first intake passage interferes with the intake air from the second intake passage. This makes it possible to generate a stronger tumble flow in the combustion chamber and make the tumble flow flow obliquely relative to an imaginary line connecting the center point of the intake valve port and the center point of the exhaust valve port, thereby suppressing the turbulence of the intake flow around the spark plug caused by the tumble flow and improving stability for lean combustion. [Effects of the Invention]

[0025] The present invention can suppress turbulence of the intake air flow around the spark plug due to tumble flow, thereby improving the stability of lean combustion. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a schematic diagram of an internal combustion engine to which an intake structure for an internal combustion engine according to the present invention is applied; [Figure 2] 2 is a plan view of a three-dimensional model of the downstream side of the intake passage of the internal combustion engine of FIG. 1. FIG. [Figure 3] FIG. 3 is a front view of the three-dimensional model of FIG. 2. [Figure 4] FIG. 3 is a bottom view of the three-dimensional model of FIG. 2. [Figure 5] FIG. 3 is a rear view of the three-dimensional model of FIG. 2. [Figure 6] FIG. 3 is a right side view of the three-dimensional model of FIG. 2. [Figure 7] FIG. 3 is a left side view of the three-dimensional model of FIG. 2. [Figure 8] FIG. 3 is a perspective view of the three-dimensional model of FIG. 2 from the left side. [Figure 9] FIG. 3 is a perspective view of the three-dimensional model of FIG. 2 from the right side. [Figure 10] FIG. 6 is a perspective view of the three-dimensional model shown in FIG. 5, and is a diagram schematically showing sprayed fuel injected from a fuel injection valve. [Figure 11] 11 is a perspective view of the three-dimensional model shown in FIG. 2, which schematically illustrates the sprayed fuel injected from the fuel injection valve, similar to that shown in FIG. 10. FIG. [Figure 12] 11 is a cross-sectional view of the three-dimensional model of FIG. 2 taken along the intake air flow direction, schematically illustrating the sprayed fuel injected from the fuel injection valve, similar to that shown in FIG. 10. FIG. [Figure 13A] 11 is a cross-sectional view of the three-dimensional model of FIG. 2 having sprayed fuel injected from a fuel injection valve similar to that shown in FIG. 10, taken along the line SA-SA of FIG. 2. [Figure 13B] 11 is a cross-sectional view of the three-dimensional model of FIG. 2 having sprayed fuel injected from a fuel injection valve similar to that shown in FIG. 10, taken along the line SB-SB of FIG. 2. [Figure 13C] 11 is a cross-sectional view of the three-dimensional model of FIG. 2 having sprayed fuel injected from a fuel injection valve similar to that shown in FIG. 10, taken along the line SC-SC of FIG. 2. [Figure 14A] 14A is a perspective view of a portion of the three-dimensional model shown in FIG. 13, and corresponds to the three-dimensional model of FIG. 13A. FIG. [Figure 14B] 14 is a perspective view of a portion of the three-dimensional model shown in FIG. 13, and corresponds to the three-dimensional model of FIG. 13B. [Figure 14C] 13B is a perspective view of a portion of the three-dimensional model shown in FIG. 13A, and corresponds to the three-dimensional model of FIG. 13C. [Figure 15] FIG. 2 is a perspective view showing a three-dimensional model of a combustion chamber and an ignition plug. [Figure 16] FIG. 2 is a top view of a three-dimensional model of a combustion chamber and an ignition plug. [Figure 17]17 is a view of the three-dimensional model of the combustion chamber and the spark plug as viewed from the XVII direction in FIG. 15. [Figure 18] FIG. 2 is a diagram showing the flow of a tumble flow on the ceiling surface of a combustion chamber. [Figure 19A] FIG. 2 is a plan view showing the positions of the initial flame and high turbulence intensity region within the combustion chamber as a result of CFD analysis of the internal combustion engine of the present invention. [Figure 19B] FIG. 1 is a plan view showing the positions of the initial flame and high turbulence intensity region within the combustion chamber as a result of CFD analysis of a conventional internal combustion engine. [Figure 20A] FIG. 19B is a side view of FIG. 19A. [Figure 20B] FIG. 19C is a side view of FIG. 19B. [Figure 21] 1 is a schematic configuration diagram of an internal combustion engine according to a first embodiment. [Figure 22] FIG. 22 is a plan view of a three-dimensional model of the internal combustion engine shown in FIG. 21, focusing on the portion from the combustion chamber to the intake system. [Figure 23] FIG. 23 is a bottom view of the three-dimensional model of FIG. 22. [Figure 24] FIG. 23 is a side view of the three-dimensional model of FIG. 22. [Figure 25] FIG. 25 is a side view corresponding to FIG. 24, schematically showing the flow of intake air from the tumble passage. [Figure 26] 6 is a side view of a three-dimensional model incorporating the three-dimensional model of FIG. 5 relating to the internal combustion engine of FIG. 1 according to a reference example. [Figure 27] FIG. 10 is a side view of a three-dimensional model having an intake structure for an internal combustion engine according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The same components (or configurations) are denoted by the same reference numerals, and the names and functions of these components are also the same. Therefore, detailed description thereof will not be repeated.

[0028] (Reference example) Before describing an embodiment of the present invention, an internal combustion engine 10 according to a reference example will be described. A schematic configuration of the internal combustion engine 10 is shown in Fig. 1. Fig. 1 is a cross-sectional view of the internal combustion engine 10 taken along an axis C (cylinder axis) of a cylinder bore 12b of a cylinder block 12 of the internal combustion engine 10. The internal combustion engine 10 is a single-cylinder engine.

[0029] A piston 15 reciprocates within a cylinder bore 12b of the cylinder block 12 and is connected to a crank pin of a crankshaft 17 in a crankcase portion 16 by a connecting rod 18. A combustion chamber 20 is defined between a top surface 15a of the piston 15, which is slidably fitted within the cylinder bore 12b of the cylinder block 12, and a combustion chamber ceiling surface 100 of the cylinder head 14 that faces the top surface 15a. The top surface 15a of the piston 15 is recessed relative to the cylinder block 12.

[0030] The internal combustion engine 10 employs a SOHC two-valve system and is provided with a valve train 22 in the cylinder head 14. A cylinder head cover 24 is placed over the cylinder head 14 to cover the valve train 22. To transmit power to the valve train 22 within the cylinder head cover 24, an endless cam chain (not shown) is installed between a camshaft 26 and the crankshaft 17, passing through the crankcase 16, the cylinder block 12, and a cam chain chamber (not shown) provided on one side of the cylinder head 14 in the crankshaft direction. The camshaft 26 rotates in synchronization with the crankshaft 17 at half the rotational speed. An ignition plug is inserted into the cylinder head 14 from the opposite side of the cam chain chamber (the other side in the crankshaft direction) toward the combustion chamber 20. In FIG. 1, the spark plug 21 facing the combustion chamber 20 is located on the front side of the page, and the cam chain chamber is located on the back side of the page.

[0031] In the cylinder head 14, an intake port 32 and an exhaust port 34 are formed, each extending while curving upward and downward from an intake valve port 28 and an exhaust valve port 30 that open to the combustion chamber ceiling surface 100. As described above, a two-valve system is employed, and a single intake port 32 and a single exhaust port 34 are defined and formed in the cylinder head 14.

[0032] The upstream end of the intake port 32 opens toward the top of the cylinder head 14 and connects to an inlet pipe 36 to form a continuous intake passage 38. A throttle body 40 is connected to the upstream side of the inlet pipe 36. The downstream end of the exhaust port 34 opens toward the bottom of the cylinder head 14 and is connected to an exhaust pipe 42. An exhaust purification device and a silencer may be provided downstream of the exhaust pipe 42.

[0033] A cylindrical intake valve guide 44 is fitted integrally to the curved outer wall portion 32a of the intake port 32 in the cylinder head 14. An intake valve 46 slidably supported by the intake valve guide 44 opens and closes the intake valve opening 28 of the intake port 32 that faces the combustion chamber 20.

[0034] In addition, an exhaust valve 50 slidably supported by an exhaust valve guide 48 integrally fitted to the curved outer wall portion 34a of the exhaust port 34 in the cylinder head 14 opens and closes the exhaust valve opening 30 of the exhaust port 34 facing the combustion chamber 20.

[0035] The intake valve 46 and the exhaust valve 50 are biased upward by valve springs so that their head portions 46a, 50a close the intake valve port 28 and exhaust valve port 30 facing the combustion chamber 20. The stem ends 46b, 50b of the intake valve 46 and the exhaust valve 50 are pushed down by the intake rocker arm 56 and the exhaust rocker arm 58, which swing against the intake cam and the exhaust cam of the camshaft 26, respectively, opening the intake valve 46 and the exhaust valve 50 at predetermined timing, connecting the intake port 32 and the combustion chamber 20, and connecting the exhaust port 34 and the combustion chamber 20, allowing intake and exhaust to occur at predetermined timing.

[0036] An inlet pipe 36 is connected to the upstream end of the intake port 32 of the internal combustion engine 10 via an insulator 60 to form a continuous intake passage 38, and a throttle body 40 is connected to the upstream side of the inlet pipe 36. The throttle body 40 has an intake passage 40a with a substantially circular cross section that forms part of the intake passage 38 leading to the combustion chamber 20 of the internal combustion engine 10, and its upstream side is connected to an air cleaner device (not shown).

[0037] The throttle body 40 is provided with a throttle valve 40c that is rotatably supported within the throttle body 40 by a throttle valve shaft 40b that is perpendicular to the flow direction of intake air in the intake passage 40a, i.e., that intersects the central axis of the intake passage 40a at a right angle, and that variably controls the flow area of ​​the intake passage 40a to open and close the intake passage 40a. The throttle valve 40c is of a butterfly type and has a throttle valve shaft 40b and a disk-shaped valve element 40d that is fixed to the throttle valve shaft 40b and rotates integrally with it.

[0038] 1 in the valve opening direction by the driver, and a return spring (not shown) biases the valve element 40d counterclockwise in the valve closing direction so that the edge of the valve element 40d abuts against the inner wall surface of the intake passage 40a in the fully closed position. The throttle valve 40c is controlled so that the intake passage 40a is slightly opened at a predetermined angle under low load operating conditions, and is fully opened under high load operating conditions.

[0039] Next, the shape of the combustion chamber 20 will be described with reference to Figures 15 to 17. Figures 15 to 17 show a three-dimensional model MC of the combustion chamber 20 on the cylinder head 14 side, and the spark plug 21. The combustion chamber is made up of a top surface 15a of the piston 15 and the opposing combustion chamber ceiling surface 100 of the cylinder head 14. The top surface 15a of the piston is concave, which allows the tumble flow, described below, to continue for a longer period of time.

[0040] 1 and 15, the combustion chamber ceiling surface 100 is formed to be recessed facing the top surface 15a of the piston 15. A general surface 100a, which is the basic shape of the combustion chamber ceiling surface 100, is formed in a roughly triangular pyramidal dome shape that continues to the outer periphery 20a of the combustion chamber 20, i.e., the outer periphery 100b of the combustion chamber ceiling surface 100.

[0041] The internal combustion engine 10 employs an SOHC two-valve system. As shown in Figure 16, an intake valve port 28 and an exhaust valve port 30 are opened on either side of the center of the combustion chamber ceiling surface 100 in the combustion chamber ceiling surface 100.

[0042] An ignition plug hole 101 opens on one side of an imaginary line L connecting the center point C1 of the intake valve port 28 and the center point C2 of the exhaust valve port 30. The spark plug 21 is inserted into the spark plug hole 101 so that its tip is oriented toward the center of the combustion chamber 20. The spark plug 21 is inserted at an angle relative to the imaginary line L and, as shown in FIG. 17 , is also inserted at an angle relative to the cylinder axis C. Although it is preferable to position the ignition point 21a of the spark plug 21 near the center of the combustion chamber ceiling surface 100, the spark plug is inserted at an angle relative to the combustion chamber 20 due to the arrangement of the two-valve intake valve 28 and exhaust valve 30. In the internal combustion engine 10, the spark plug 21 is inserted at an angle with respect to the imaginary line L, but it is not necessarily required to be inserted at an angle with respect to the imaginary line L, and it may be inserted at a right angle with respect to the imaginary line L. Also, in the internal combustion engine 20, the spark plug 21 is inserted at an angle with respect to the cylinder axis C, but it is not necessarily required to be inserted at an angle with respect to the cylinder axis C, and it may be inserted perpendicular to the cylinder axis C or along the cylinder axis.

[0043] As shown in FIGS. 16 and 17, a recess 102 is formed in the combustion chamber ceiling surface 100 so as to be recessed from a general surface 100a of the combustion chamber ceiling surface 100.

[0044] In the internal combustion engine 10 described above, an intake structure S0 is configured to impart a tumble vortex, i.e., tumble flow, i.e., vertical rotation, to the fuel-air mixture in the combustion chamber 20 to achieve more favorable combustion of the fuel or air-fuel mixture in the combustion chamber 20. The intake structure S0 includes a partition 62 provided in the intake passage 38 to divide the intake passage 38 into multiple sections in the direction of the cylinder axis C. That is, the intake passage 38 is divided along the intake air flow direction by the partition 62 extending from the inlet pipe 36 to the intake port 32 into a tumble passage 64 configured to generate a tumble flow in the combustion chamber 20 through the intake air that passes through it, and a main passage 66 excluding the tumble passage 64. The tumble passage 64 corresponds to the first intake passage, and the main passage 66 corresponds to the second intake passage. The tumble passage 64 may also be referred to as a secondary passage.

[0045] The partition 62, which extends like a plate in the intake air flow direction, is provided so as to substantially vertically divide the downstream side of the intake passage 38 into two, here extending substantially parallel to the axis extending in the flow direction. In this embodiment, the flow path cross-sectional area of ​​the tumble passage 64 is smaller than the flow path cross-sectional area of ​​the main passage 66. However, the partition 62 may be provided so that the flow path cross-sectional area of ​​the tumble passage 64 is larger than the flow path cross-sectional area of ​​the main passage 66, or the flow path cross-sectional areas may be substantially the same.

[0046] The lower portion of the intake passage 38 separated by the partition 62 is the tumble passage 64, and the upper portion is the main passage 66, but in this specification they are not limited to being arranged vertically. Note that in this specification, "up" and "down" with respect to the intake passage 38, etc., refer to the direction from the crankshaft 17 side to the cylinder head 14 or cylinder head cover 24 side in the direction of the cylinder axis C as the "up" or "upward" direction, and the direction opposite to this "up" direction, i.e., from the cylinder head 14 side to the crankshaft 17 side as the "down" or "downward" direction, and do not refer to absolute "up" and "down" in space. The "up" or "upward" direction corresponds to the first direction, and the "down" or "downward" direction corresponds to the second direction.

[0047] An intake control valve may be further provided upstream of the partition 62 and downstream of the throttle valve 40c. This intake control valve may be provided to variably control the flow path area of ​​the main passage 66, for example. The intake control valve may also be called a tumble valve, tumble control valve, or TCV, and is controlled to fully close the main passage 66 under low load operating conditions and fully open the main passage 66 under high load operating conditions. The throttle valve 40c is electronically controlled as described below, but is not limited to being electronically controlled and may be a valve that is mechanically controlled by a throttle cable, for example. This also applies when an intake control valve is provided.

[0048] The internal combustion engine 10 is provided with fuel injection valves 68 and 70. One fuel injection valve (hereinafter referred to as the first fuel injection valve) 68 is provided upstream of the upstream end 62u of the partition portion 62 and is configured to inject fuel into a portion of the intake passage 38 upstream of the upstream end 62u. The other fuel injection valve (hereinafter referred to as the second fuel injection valve) 70 is configured to inject fuel into the intake port 32. The second fuel injection valve 70 is provided to face the main passage 66 and is provided in the inlet pipe 36 in this example. As such, the second fuel injection valve 70 is configured to inject fuel from the main passage 66 side and supply fuel to the combustion chamber 20 through the intake port 32. As is clear from FIG. 1 , the second fuel injection valve 70 is attached to an upper wall portion of a member that defines the intake passage 38. The present disclosure does not limit the number of fuel injection valves to two and may, for example, be one. In this case, for example, only the second fuel injection valve 70 may be provided.

[0049] An ECU (electronic control unit) 72 that controls the internal combustion engine 10 has a configuration as a so-called computer, and includes an intake control unit 74 and a fuel injection control unit 76. That is, the ECU 72 includes a processor (e.g., a CPU) and memory (e.g., a ROM and a RAM). The ECU 72 analyzes the operating state of the internal combustion engine 10 based on outputs from various sensors such as an engine rotation speed sensor and an engine load sensor, and controls the operation of the throttle valve 40c using the intake control unit 74. Furthermore, the ECU 72 controls the operation of each of the fuel injection valves 68, 70 using the fuel injection control unit 76 based on the analyzed operating state of the internal combustion engine 10. The ECU 72 stores programs and various data for these controls.

[0050] 2 to 9 show a three-dimensional model M of the downstream side of the intake passage 38. The three-dimensional model M extends from the downstream end of the inlet pipe 36 to the intake port 32, and terminates downstream at the intake valve port 28. Since the three-dimensional model M is a model of the downstream end of the intake passage 38, the outer surface 80 of the three-dimensional model M has portions corresponding to the inner surface 36s of the inlet pipe 36, the inner surface 60s of the insulator 60, and the inner wall surface 14s of the cylinder head 14, which are members that define the downstream side of the intake passage 38. A portion of the outer surface 80 of the three-dimensional model M corresponds to the surface 62s of the partition portion 62, and a portion corresponds to the surface 90s of the offset portion 90, which will be described later. Therefore, to facilitate understanding, the portions of the three-dimensional model M that correspond to the inner surface 36s of the inlet pipe 36, the inner surface 60s of the insulator 60, the inner wall surface 14s of the cylinder head 14, the surface 62s of the partition portion 62, and the surface 90s of the offset portion 90 are denoted by their corresponding reference numerals. The portion where the second fuel injection valve 70 is attached and where its injection port faces the intake passage 38 (hereinafter referred to as the attachment portion) is denoted by the symbol "70s." Furthermore, the symbol "U" is used for the upper side in the direction of the cylinder axis C, the symbol "D" is used for the lower side, and the symbol "R" is used for the right side when viewed from upstream to downstream in the intake air flow direction, and the symbol "L" is used for the left side.

[0051] 1 and 2 to 9, the partition 62 has a deviation portion 90 on its downstream side that is narrower in the left-right direction (LR direction) intersecting the cylinder axis C, i.e., in the width direction, than the upstream end 62u of the partition 62. The deviation portion 90 is a narrow portion of the partition 62 in the width direction, which can be defined as the direction extending from one side of the valve axis of the intake valve 46 to the other when facing the intake valve 46 in the direction in which intake air flows from upstream to downstream through the intake passage 38, i.e., in the intake air flow direction. As shown in FIG. 4, in the tumble passage 64, the width W2 of a downstream end portion 64d is clearly narrower than the width W1 of an upstream end portion located on the upstream end 62u side of the partition 62 within the portion defined by the cylinder head 14. Since the partition portion 62 is provided and formed so as to define the tumble passage 64 in the intake passage 38, the offset portion 90 with respect to the portion of width W2 is relatively narrow.

[0052] Furthermore, the deviation portion 90 is biased in one direction in the left-right direction, i.e., the width direction. Here, the downstream end portion 64d of the tumble passage 64 is defined so as to be biased toward the right R side. Therefore, the deviation portion 90 downstream of the partition portion 62, which at least partially defines the biased downstream end portion 64d of the tumble passage 64, is biased toward the right R side here. Therefore, in FIG. 1, the cylinder axis C extends parallel to the paper surface and the width direction extends approximately perpendicular to the paper surface, so the deviation portion 90 extending downstream of the partition portion 62 does not appear and is therefore indicated by a two-dot dashed line rather than a solid line. Therefore, the confluence 65 of the main passage 66 and the tumble passage 64 is biased toward the right R side.

[0053] 6 and 7, the mounting portion 70s of the second fuel injection valve 70 is positioned on the left side L of the intake passage 38. In this way, the second fuel injection valve 70 is provided at a position offset in a direction opposite to the offset direction of the offset portion 90. In this way, the second fuel injection valve 70 is provided so as to be able to inject fuel in a direction different from, and more preferably in the opposite direction to, the offset direction of the offset portion 90. The second fuel injection valve 70 is provided on the upper side, i.e., on the main passage 66 side, and injects fuel from the main passage 66 side.

[0054] FIG. 10, which is a perspective view of the three-dimensional model M shown in FIG. 5, schematically illustrates the sprayed fuel F injected from the second fuel injection valve 70, which is located off to the left (L) side. FIG. 11 is a perspective view of the three-dimensional model M, which schematically illustrates the sprayed fuel F injected from the fuel injection valve, similar to that shown in FIG. 10. FIG. 12 is a cross-sectional view of the three-dimensional model M, taken along the intake air flow direction, which also schematically illustrates the sprayed fuel F injected from the fuel injection valve, similar to that shown in FIG. 10. From FIGS. 10 to 12, it can be seen that the fuel F injected from the second fuel injection valve 70 is not blocked by the partition portion 62, but at least a portion of it, particularly at least a majority of it, and more preferably all of it, first flows through the main passage 66, then flows to the junction 65 between the main passage 66 and the tumble passage 64, and then directly reaches the intake valve port 28 and is introduced into the combustion chamber 20. The arrangement of the second fuel injection valve 70 and the shape of the partition portion 62 including the offset portion 90 are designed to enable such fuel injection. In particular, the partition body portion 92 of the partition portion 62 terminates on its downstream side to enable the main passage 66 and the tumble passage 64 to merge, and the partition body portion 92 and the offset portion 90 of the partition portion 62 are designed so that the fuel F injected from the second fuel injection valve 70 reaches the intake valve port 28 along a surface 90s of the offset portion 90, preferably without touching the offset portion 90 (see, for example, FIG. 11 ).

[0055] Here, cross-sectional views of the three-dimensional model M including the injected fuel F of Figure 10 are shown in Figures 13A to 14C. However, Figure 13A is a cross-sectional view of the three-dimensional model M taken along line SA-SA in Figure 2, Figure 13B is a cross-sectional view of the three-dimensional model M taken along line SB-SB in Figure 2, and Figure 13C is a cross-sectional view of the three-dimensional model M taken along line SC-SC in Figure 2. Figures 14A to 14C are perspective views of portions of the three-dimensional model M of Figures 13A to 13C, with the three-dimensional model of Figure 14A corresponding to the three-dimensional model of Figure 13A, the three-dimensional model of Figure 14B corresponding to the three-dimensional model of Figure 13B, and the three-dimensional model of Figure 14C corresponding to the three-dimensional model of Figure 13C.

[0056] 13A and 14A, the tumble passage 64 and the main passage 66 are completely separated. At the position of line SA-SA in Fig. 2, the partition portion 62 extends to the inner surface 36s of the inlet pipe 36 at both ends in the width direction between the tumble passage 64 and the main passage 66, and a partition main body portion 92 connecting to the upstream side of the deviation portion 90 extends thereto. Note that in Figs. 13A and 14A, the surface 62s of the partition portion 62 and the surface 92s of the partition main body portion 92 therein are denoted by the same reference numerals.

[0057] 13B and 14B, the tumble passage 64 and the main passage 66 are partially connected. Also, in the cross sections of FIGS. 13B and 14B, the surface 62s of the partition 62 extends in the width direction and also in the up-down direction, and is biased to the right. From this, it can be seen that, at the position of line SB-SB in FIG. 2, the partition 62 transitions from the partition main body 92 to the offset portion 90, and the offset portion 90 extends from the right side of the inner wall surface 14s of the cylinder head 14 to the left of the intake port 32, without completely separating the tumble passage 64 and the main passage 66. In other words, the tumble passage 64 and the main passage 66 are partitioned so that the main passage 66 and the tumble passage 64 are connected in the region where the offset portion 90 extends in the intake air flow direction. In other words, the deviation portion 90 connected to the partition main body portion 92 extends downstream of the partition main body portion 92 of the partition portion 62 so as to extend a portion of the partition main body portion 92 in the flow direction downstream of the partition main body portion 92. Note that in Figures 13B and 14B, the portions corresponding to the surface 62s of the partition portion 62 and the surface 90s of the deviation portion 90 thereon are denoted by the same reference numerals, and this is also true in Figures 13C and 14C.

[0058] 13C and 14C, the amount by which the deviation portion 90 protrudes leftward from the inner wall surface of the cylinder head 14 is reduced compared to the cut portions of FIGS. 13B and 14B. Thus, the deviation portion 90 is formed so as to narrow downstream in the intake air flow direction. This results in a greater degree of communication between the main passage 66 and the tumble passage 64 at the cut portions of FIGS. 13C and 14C than at the cut portions of FIGS. 13B and 14B. In other words, the amount of communication between the tumble passage 64 and the main passage 66 at the cut portions of FIGS. 13C and 14C is greater than the amount of communication between them at the cut portions of FIGS. 13B and 14B. More specifically, the tumble passage 64 and the main passage 66 are partitioned so that the main passage 66 extends downward to the side of the deviation portion 90 in the region where the deviation portion 90 extends in the intake air flow direction. This downward expansion of the main passage 66 is carried out in the direction opposite to the direction in which the deviation section 90 is biased, and in this case, it is carried out on the left side L of the deviation section 90. Note that this downward expansion of the main passage 66 and the resulting merging of the main passage 66 and the tumble passage 64 are more pronounced downstream of the deviation section 90.

[0059] 13A to 14C, the second fuel injection valve 70, which is arranged to inject fuel F from the main passage 66 toward the combustion chamber 20, is arranged to inject fuel in a direction opposite to the biased direction of the deviation portion 90. Therefore, the partition portion 62, and particularly the deviation portion 90, can be extended further downstream in the intake flow direction. The tumble passage 64 is then defined and formed so as to be biased downstream of the biased direction of the deviation portion 90. Therefore, the deviation portion 90 of the partition portion 62, which is extended further downstream in the intake flow direction, can impart stronger directionality to the intake air from the tumble passage 64.

[0060] Thus, the partition 62 completely separates the main passage 66 from the tumble passage 64 with its upstream partition body 92, and has a downstream offset portion 90 that connects the main passage 66 and the tumble passage 64 while characterizing the flow from the tumble passage 64 further downstream. The second fuel injection valve 70 is positioned offset from the offset portion 90, on the opposite side in the width direction. This allows the second fuel injection valve 70 to inject fuel in a direction different from the offset portion 90, thereby introducing fuel into the combustion chamber 20 generally directly through the intake valve port 28. This ensures a good supply of fuel to the combustion chamber. Therefore, the offset portion 90, which is the downstream portion of the partition 62, can be extended further downstream. This allows the flow from the tumble passage 64 to be more directional. This directionality is directed between the intake valve port 28 and the head portion 46a of the intake valve 46 when the valve is open so as to form a stronger tumble flow in the combustion chamber 20, so that the intake air from the tumble passage 64 can more suitably form a tumble flow in the combustion chamber 20.

[0061] The tumble passage 64 and the main passage 66 are partitioned so that the tumble passage 64 communicates with the main passage 66 downstream of the downstream edge of the partition portion 62, i.e., the downstream edge 90d of the offset portion 90, to form a single intake passage leading to the combustion chamber 20. This allows intake air from the tumble passage 64 to be introduced into the combustion chamber 20 together with intake air from the main passage 66, making it possible to supply fuel to the combustion chamber 20 and create a tumble flow with intake air from the single intake port 32, which is a single intake passage. This configuration also makes it possible to suppress an increase in the number of parts and is advantageous in terms of cost.

[0062] Because the tumble passage 64 and the main passage 66 are configured as described above, the intake air flowing into the combustion chamber 20 from the intake port is given strong directionality by the flow from the tumble passage 64, and as shown in Figure 18, the tumble flow flows along the combustion chamber ceiling surface 100, at an angle to the imaginary line L connecting the center point C1 of the intake valve port 28 and the center point C2 of the exhaust valve port 30. The tumble flow that has flowed into the combustion chamber 20 flows in an ellipse within the approximately egg-shaped combustion chamber formed by the piston recess 15b of the top surface 15a of the piston 15 and the combustion chamber ceiling surface 100, as shown in Figure 17.

[0063] Generally, lean combustion in internal combustion engines tends to be unstable, which leads to poor fuel economy and emissions. Shortening the initial combustion period is an effective way to improve combustion stability, but this is greatly affected by the discharge pattern of the spark plug 21. It is important that the flow of intake air around the spark plug 21 is at a certain speed and that the variation in the intake air flow is minimized.

[0064] As shown in Figure 18, the recess 102 provided in the combustion chamber ceiling surface 100 is arranged obliquely with respect to the imaginary line L connecting the center point C1 of the intake valve port 28 and the center point C2 of the exhaust valve port 30, and upstream of the ignition plug 21 in the direction of the tumble flow flowing in along the combustion chamber ceiling surface 100.

[0065] As shown in Figures 15 to 17, the recess 102 is formed so as to be continuous with the spark plug hole 101 into which the spark plug 21 is inserted, and is formed continuously from the outer circumferential portion 100b of the combustion chamber ceiling surface 100 toward the spark plug hole 101. The recess 102 has a uniform depth, but may be gradually deeper from the outer circumferential portion 100b toward the spark plug hole 101. The cross-sectional shape of the recess 102 may be rectangular, U-shaped, V-shaped, or the like, but it is preferable that the cross-sectional area does not change drastically. By making the recess 102 deeper relative to the general surface 100a of the combustion chamber ceiling surface 100, turbulence of the tumble flow flowing along the wall surface of the combustion chamber 20 around the spark plug hole 101 can be reduced, thereby stabilizing the ignited flame.

[0066] As shown in Figure 18, it is preferable that the recess 102 formed in the combustion chamber ceiling surface 100 is formed so as to extend from the upstream side of the tumble flow, i.e., from the outer peripheral portion 100b of the combustion chamber ceiling surface 100, and connect to the ignition plug hole 101.

[0067] The position of the center of gravity CG of the volume of the combustion chamber of an internal combustion engine is shown in Figures 19 and 20. Figures 19A and 20A show the center of gravity CG of the volume of the combustion chamber of a conventional internal combustion engine that does not have a recess 102 in the combustion chamber ceiling surface 100. The conventional internal combustion engine is configured the same as the internal combustion engine 10 of the present invention, except that it does not have a recess. Figures 19B and 20B show the center of gravity CG of the volume of the combustion chamber 20 of the internal combustion engine 10 of the present invention, in which a recess 102 is provided in the combustion chamber ceiling surface 100. Figure 20A is a view taken along the arrow XXA in Figure 19. Figure 20B is a view taken along the arrow XXB in Figure 19.

[0068] 19A, the center of gravity CG of the volume of the combustion chamber of a conventional internal combustion engine that does not have the recess 102 is located on an imaginary line L that connects the center point C1 of the intake valve port 28 and the center point C2 of the exhaust valve port 30. Since the internal combustion engine 10 of the present invention has the recess 102, as shown in FIG. 19B, the center of gravity CG of the volume of the combustion chamber 20 is located closer to the intake valve port 28 and the spark plug hole 101 into which the spark plug 21 is inserted with respect to the imaginary line L, and is located upstream of the spark plug hole 101 in the flow direction of the tumble flow that flows on the combustion chamber ceiling surface 100. In the present internal combustion engine 20, the center of gravity CG is located upstream of the spark plug hole 101 in the flow direction of the tumble flow that flows on the combustion chamber ceiling surface 100, but it does not necessarily have to be located upstream of the spark plug hole 101.

[0069] In this way, the recess 102 is provided in the combustion chamber ceiling surface 100 upstream of the spark plug 21 in the direction of the tumble flow in, which suppresses the variation in the tumble flow toward the spark plug 21 and improves the uniformity of the tumble flow. This reduces the variation in the intake air flow around the spark plug 21, stabilizing combustion during lean combustion.

[0070] Furthermore, since the recess 102 is formed continuously from the outer peripheral portion 100b of the combustion chamber ceiling surface 100, no edge shape is generated around the spark plug, and the flow of the tumble flow is not obstructed by the edge shape, thereby improving the flow of the tumble flow.

[0071] Furthermore, since the recess 102 is formed continuously from the outer periphery 100b of the combustion chamber ceiling surface 100 toward the spark plug hole 101, the shape of the combustion chamber does not become complicated, and manufacturing costs can be reduced.

[0072] Furthermore, the recess 102 has a uniform cross-sectional area perpendicular to the flow direction of the tumble flow flowing on the combustion chamber ceiling surface 100, so that there is little change in the cross-sectional area in the flow direction of the tumble flow, which can further suppress turbulence of the intake flow flowing around the spark plug 21, allowing the tumble flow to flow stably, thereby further improving stability for lean combustion.

[0073] Furthermore, by positioning the volume center of gravity CG of the combustion chamber 20 on the intake valve port 28 side and closer to the spark plug hole 101 into which the spark plug 21 is inserted with respect to the imaginary line L, the high turbulence intensity region can be brought closer to the initial flame without increasing the average turbulence intensity of the intake air in the combustion chamber, thereby promoting stable flame growth even in lean conditions.

[0074] An analysis was performed using CFD (Computational Fluid Dynamics) on an internal combustion engine provided with the recessed portion 102 and a conventional internal combustion engine not provided with the recessed portion. The conventional internal combustion engine and the internal combustion engine of the present invention have the same configuration except for the presence or absence of the recessed portion. The analysis results are shown in Figures 19 and 20. The state immediately after ignition is shown with the flame region in black and the high turbulence intensity region in gray.

[0075] 19A and 20A, in a conventional two-valve internal combustion engine that uses tumble flow to perform lean combustion, the ignition plug 21 is located to the side of an imaginary line L that connects the center point C1 of the intake valve port 28 and the center point C2 of the exhaust valve port 30, and the center of gravity CG of the volume is located on the imaginary line L. This causes uneven flame growth, which increases the combustion period and causes torque variations.

[0076] In the combustion chamber 20 of the internal combustion engine 10 of the present invention, as described above, the recess 102 is provided in the combustion chamber ceiling surface, and the volume center of gravity CG of the combustion chamber 20 is located closer to the intake valve port 28 and the spark plug hole 101 with respect to the imaginary line L. With this configuration, as shown in Figures 19B and 20B, a region of high turbulence intensity is generated near the initial flame, which promotes stable flame growth even in a lean condition. (First embodiment) As described above, the intake structure S0 for the internal combustion engine 10 having the above configuration provides excellent functions and effects. The following describes an internal combustion engine 110 according to the first embodiment of the present invention, particularly its intake structure S, which has a configuration aimed at further strengthening the tumble flow in addition to the above configuration. The intake structure S for the internal combustion engine 110 generally has the above-described configuration of the intake structure S0 for the internal combustion engine 10, and has additional configurations, or features. Therefore, the following description will mainly focus on the internal combustion engine 110, focusing on differences from the internal combustion engine 10. Components that are equivalent to or correspond to components already described in the internal combustion engine 110 will be designated by the same reference numerals, and further redundant description will be omitted. Note that while the internal combustion engine 110 is a single-cylinder engine, the internal combustion engine to which the present invention is applied is not limited to single-cylinder engines and may be multi-cylinder engines.

[0077] As shown in Fig. 21, compared to the internal combustion engine 10, the internal combustion engine 110 does not include the first fuel injection valve 68, but includes a fuel injection valve 70a corresponding to the second fuel injection valve. Note that the internal combustion engine 110 may also include the first fuel injection valve 68, as with the internal combustion engine 10. The internal combustion engine 110 also includes the tumble valve 94c described above so as to be able to open and close the main passage 66 partitioned by the partition portion 62. A tumble valve body 94 is connected to the upstream end of the inlet pipe 36 via an insulator 95. The tumble valve body 94 has an intake passage 94a with a substantially circular cross section that constitutes part of the intake passage 38, and the throttle body 40 described above is connected to the upstream end of the tumble valve body 94.

[0078] The tumble valve body 94 is rotatably supported within the tumble valve body 94 by a valve stem 94b that is perpendicular to the intake air flow direction of the intake passage 94a, i.e., that intersects the center axis of the intake passage 94a at a right angle. The tumble valve 94c variably controls the flow area of ​​the intake passage 94a and opens and closes the upper region of the intake passage 94a in cooperation with the partition 62. The operation of the tumble valve 94c is electronically controlled in this example according to the operating state of the internal combustion engine 110, but is not limited to this. For example, the tumble valve 94c is controlled so as to fully close the main passage 66 under low-load operating conditions and fully open the main passage 66 under high-load operating conditions. The tumble valve 94c is of a butterfly type and includes a valve stem 94b and a generally disk-shaped valve element 94d that is fixed to the valve stem 94b and rotates integrally therewith. In this way, the tumble valve 94c is configured to include a valve body 94d, which is a single valve member that rotates integrally with the valve shaft 94b. However, the valve shaft 94b of the tumble valve 94c is parallel to the throttle valve shaft 40b.

[0079] The internal combustion engine 110 is characterized by the tumble passage 64. The tumble passage 64 will be described with reference to FIGS.

[0080] 22 to 24 show a three-dimensional model M1 extending from the top of the combustion chamber 20 of the internal combustion engine 110 to the downstream side of the intake system, for example, the intake port 32. FIG. 22 is a plan view or top view of the three-dimensional model M1, corresponding to the plan view of the internal combustion engine 10 (FIG. 2). FIG. 23 is a bottom view of the three-dimensional model M1, corresponding to the bottom view of the internal combustion engine 10 (FIG. 4). FIG. 24 is a side view of the three-dimensional model M1, corresponding to the rear view of the internal combustion engine 10 (FIG. 5). In the internal combustion engine 110, as in the internal combustion engine 10, the intake passage 38 connected to the combustion chamber 20 is divided by a partition 62 in the direction of the cylinder axis C into a tumble passage 64, which is a first intake passage, and a main passage 66, which is a second intake passage. The main passage 66 is provided above the tumble passage 64 in the direction of the cylinder axis C. In a top view (FIG. 22) seen from the direction of the cylinder axis C, the tumble passage 64 roughly overlaps with the main passage 66, and the junction 65 of the tumble passage 64 with the main passage 66 is biased toward the right R side with respect to the opening of the intake port 32, i.e., the intake valve port 28, as already explained. Furthermore, in the internal combustion engine 110, the tumble passage 64 provided to generate a tumble flow in the combustion chamber 20 is curved so as to move away from the main passage 66 in the direction of the cylinder axis C, and is also curved in the width direction perpendicular to the cylinder axis C and perpendicular to the intake / exhaust direction.

[0081] 22 and 23, an imaginary plane IS is drawn that includes the cylinder axis C and extends in the intake / exhaust direction. This imaginary plane IS extends in the intake / exhaust direction, passes through the centers of the intake valve port 28 and the exhaust valve port 30, and includes the cylinder axis C. It is represented in FIGS. 22 and 23 as a line (center line) Lx. Comparing the imaginary plane IS with the center line Lx reveals that the main passage 66 is formed such that its width in the left-right direction simply narrows downstream from the upstream side toward the downstream side, i.e., toward the combustion chamber 20. Meanwhile, in the three-dimensional model M1 of the internal combustion engine 110 of this embodiment, the right-side contour 64r of the tumble passage 64 is not parallel to the center line Lx but curves convexly outward to the right. As the contour 64r extends from the upstream side to the downstream side in the intake air flow direction, it first widens, protruding outward to the right, and then extends toward the center line Lx after passing through a maximum rightward protrusion 64s. 22, the tumble passage 64 is formed so as to curve convexly toward the same side as the side to which the junction 65 is biased. In this way, in the internal combustion engine 110, the tumble passage 64 is formed so as to curve in the width direction, i.e., the left-right direction, which is perpendicular to the cylinder axis C and perpendicular to the intake / exhaust direction, i.e., the line Lx.

[0082] Furthermore, as shown in FIG. 24 , in the three-dimensional model M1, the tumble passage 64 curves away from the main passage 66. The partition 62 is provided midway through the intake passage 38, where the tumble passage 64 branches off from the main passage 66 and merges with the main passage 66 downstream. By curving away from the main passage 66, the tumble passage 64 curves convexly in the opposite direction from the main passage 66. More specifically, the tumble passage 64 is curved convexly toward the crankshaft 17 in the direction of the cylinder axis C, i.e., it curves convexly downward. In FIG. 24 , a plane, i.e., a line Ly, is drawn that is perpendicular to the cylinder axis C and tangent to a lower contour 64t of the tumble passage 64. The contour 64t first protrudes downward from the upstream side to the downstream side in the intake air flow direction, passes through a maximum downward protrusion 64u, and then extends upward. The contour 64t is tangent to the line Ly not at either end, but at the maximum protrusion 64u. The vertical width of the tumble passage 64 does not change significantly from the upstream side to the downstream side in the intake air flow direction. Therefore, in the internal combustion engine 110, in a side view (FIG. 24) seen from a direction perpendicular to the cylinder axis C, the tumble passage 64 curves in the direction of the cylinder axis C. More specifically, around the maximum downward protrusion 64u, the tumble passage 64 curves in a substantially U-shape so as to be most downwardly convex in the direction of the cylinder axis C. Therefore, in FIG. 24, the downstream portion 64L of the tumble passage 64 is formed so as to approach the cylinder head 14 from the crankshaft 17 side in the direction of the cylinder axis C as it approaches the downstream side in the intake air flow direction. In particular, the downstream portion 64L of the tumble passage 64 includes the portion of the tumble passage 64 downstream of the maximum protrusion 64u. Because the vertical width of the tumble passage 64 does not change significantly from the upstream side to the downstream side in the intake air flow direction, the curved shape of this contour 64t is the same in the wall surface ds of the partition 62 that defines the tumble passage 64 in a side view seen from a direction perpendicular to the cylinder axis C, i.e., in Figure 24, the wall surface ds of the partition 62 that defines the tumble passage 64 is curved so as to convex toward the crankshaft 17 in the direction of the cylinder axis C.

[0083] 22, that is, in a top view seen from the direction of the cylinder axis C, a confluence portion 65 and an ignition plug facing the combustion chamber 20 are arranged on one side, in this case the right R side, of an imaginary plane IS that includes the cylinder axis C and extends in the intake and exhaust direction. In FIG. 22, an ignition portion p of the spark plug is shown.

[0084] According to the intake structure S of the internal combustion engine 110 having the above-described configuration, the following effects are achieved.

[0085] For example, when the tumble valve 94c is closed, intake air is allowed to flow into the combustion chamber 20 from the tumble passage 64 during the intake stroke, thereby generating a tumble flow in the combustion chamber 20. However, between one intake stroke and the next, intake air stagnates in the main passage 66 via the junction 65. FIG. 26 shows a three-dimensional model M2 incorporating the three-dimensional model M of the intake structure S0 of the internal combustion engine 10 of the reference example. In the three-dimensional model M2 of FIG. 26, a throttle valve 40c and a tumble valve 94c downstream thereof (not shown) are provided upstream of the tumble passage 64 and the main passage 66, as already explained. When the throttle valve 40c is opened and the tumble valve 94c is fully closed, as shown in FIG. 26, when the intake valve is opened during the intake stroke, intake air passing around the throttle valve 40c flows into the tumble passage 64 and into the combustion chamber 20 (see arrow A1). At this time, the intake air remaining in the main passage 66 is also drawn into the combustion chamber 20, but flows in a manner that intersects with the intake air from the tumble passage 64 (see arrow A2). Therefore, the flow of intake air from the main passage 66 could affect the flow of intake air from the tumble passage 64. In contrast, the intake structure S1 of the internal combustion engine 110 configured as described above has the above configuration, and can alleviate this effect.

[0086] In the intake structure S of the internal combustion engine 110, the intake passage 38 is divided by a partition 62, and a main passage 66 is formed above the tumble passage 64. That is, in the direction of the cylinder axis C, the intake passage 38 connected to the combustion chamber 20 is provided with the tumble passage 64 for generating a tumble flow in the combustion chamber 20 and the main passage 66 overlapping each other. The tumble passage 64 is formed so as to curve in a width direction perpendicular to the cylinder axis C and perpendicular to the intake / exhaust direction. Therefore, for example, when the throttle valve 40c is open and the tumble valve 94c is closed (e.g., during light load operation), and the intake valve 46 is opened, the intake air from the tumble passage 64 flows into the combustion chamber 20 from the right side of the intake air from the main passage 66 through the junction 65. This reduces the degree of interference between the intake air from the tumble passage 64 and the intake air from the main passage 66, making it possible to favorably form a tumble flow in the combustion chamber. Furthermore, the tumble passage 64 curves away from the main passage 66 in the direction of the cylinder axis C. Therefore, the intake air from the tumble passage 64 can smoothly flow into the combustion chamber 20 to form a tumble flow. Therefore, a stronger tumble flow can be generated in the combustion chamber.

[0087] In particular, in the intake structure S, the confluence portion 65 is biased relative to the opening 28 of the intake port 32 in the top view of Figure 22. Therefore, it is possible to set an angle corresponding to the bias of the flow of intake air that flows into the combustion chamber when the intake valve 46 opens during the intake stroke. Furthermore, the tumble passage 64 is formed so as to curve convexly toward the same side as the bias of the confluence portion 65. This further reduces the degree to which the intake air from the tumble passage 64 interferes with the intake air from the main passage 66, making it possible to favorably form a tumble flow in the combustion chamber.

[0088] Furthermore, in FIG. 24 , the tumble passage 64 is curved convexly toward the crankshaft 17 in the direction of the cylinder axis C. This actively encourages the intake air from the tumble passage 64 to separate from the walls that define the tumble passage 64 at the junction 65, particularly the wall 64w that defines the lower contour 64t of the tumble passage 64. The flow of intake air from the tumble passage 64 at this time is indicated by arrow A3 in FIG. 25 . This increases the flow velocity of the intake air from the tumble passage 64, enabling the generation of a stronger tumble flow. Furthermore, because the tumble passage 64 is curved convexly toward the crankshaft 17 in the direction of the cylinder axis C, the position of the junction 65 is located above the portion 46s of the intake valve 46 that abuts the head portion 46a, as shown in FIG. 25 . By adjusting the position of the junction 65 based on experiments or the like, the direction of the intake air from the tumble passage 64 can be optimized, further encouraging the generation of a tumble flow.

[0089] 24, the downstream portion 64L of the tumble passage 64 is formed so that the further downstream in the intake air flow direction it is, the closer it is to the cylinder head 14 in the direction of the cylinder axis C, from the crankshaft 17. Therefore, it is possible to more actively encourage the intake air from the tumble passage 64 to separate from the wall portion 64w that defines the lower contour 64t of the tumble passage 64.

[0090] 24, the wall surface ds of the partition 62 that defines the tumble passage 64 is curved so as to convex toward the crankshaft 17 in the direction of the cylinder axis C. Therefore, the width of the tumble passage in the vertical direction can be made roughly the same, and the intake air from the tumble passage 64 can be directed to generate a greater tumble flow. Note that the wall surface ds is the wall surface on the side of the main passage 66 that defines the tumble passage 64.

[0091] 22, on one side of an imaginary plane IS that includes the cylinder axis C and extends in the intake and exhaust direction, in this case on the right R side, the confluence section 65 and the spark plug facing the combustion chamber 20 are arranged. Therefore, the intake air from the tumble passage 64 can more quickly transport the spark from the spark plug to the center of the combustion chamber, thereby making it possible to further increase the flame propagation speed.

[0092] (Second embodiment) Next, a second embodiment will be described. The following mainly describes the differences, i.e., the features, of the second embodiment from the first embodiment. However, in the following, the same reference numerals as already used are used for components that are equivalent to or correspond to components already described, and further overlapping explanations will be omitted.

[0093] The internal combustion engine of the second embodiment has the features of the internal combustion engine 110 of the first embodiment, for example, the above-described configuration of the tumble passage 64, but has an additional feature in the configuration of the main passage 66 compared to the internal combustion engine 110. This feature will be described with reference to FIG. 27. FIG. 27 shows a three-dimensional model M3 having an intake structure S1 for an internal combustion engine according to the second embodiment. In FIG. 27, a throttle valve 40c and a tumble valve 94c (not shown) are provided upstream of the tumble passage 64 and the main passage 66, and the throttle valve 40c is fully open and the tumble valve 94c is fully closed.

[0094] In the intake structure S1 for an internal combustion engine according to the second embodiment, as shown in FIG. 27 , which is a side view taken from a direction perpendicular to the cylinder axis C, the downstream wall surface us of the partition 62 that defines the main passage 66 is the downstream wall surface that defines the tumble passage 64 side of the main passage 66, and has a curved shape that corresponds to the curved shape of the downstream portion 64L of the tumble passage 64. This means that the curved shape of the downstream wall surface us is similar to or close to, or preferably identical to, the curved shape of the downstream portion 64L. As previously described with reference to FIG. 24 , the downstream portion 64L of the tumble passage 64 is formed such that, as it becomes more downstream in the intake air flow direction, it approaches the cylinder head 14 from the crankshaft 17 side in the direction of the cylinder axis C. In particular, the downstream wall surface us of the partition 62 that defines the main passage 66 has this upwardly curved shape. This curved shape of the downstream wall surface us results in the downstream wall surface us having a downwardly convex or nearly downwardly convex curve.

[0095] By having the above-described configuration of the downstream wall surface us of the partition portion 62 that defines the main passage 66, for example, when the tumble valve 94c is in an operating state where it is closed, the intake air in the main passage 66 (see arrow A4) can jump at the downstream wall surface us toward the combustion chamber 20 and is directed to smoothly merge with the intake air from the tumble passage 64 (see arrow A5). This makes it possible to promote the generation of a stronger tumble flow.

[0096] Although the embodiments and modifications thereof according to the present invention have been described above, the present invention is not limited thereto. Various substitutions and modifications are possible without departing from the spirit and scope of the present invention as defined by the claims of this application.

[0097] In the intake structures S, S1 for an internal combustion engine according to the first and second embodiments, the tumble passage 64 is curved and biased to the right, but it may also be curved and biased to the left. In this case, the junction 65 and the spark plug may be provided on the left side of the imaginary plane IS. Note that the intake structures S, S1 for an internal combustion engine according to the first and second embodiments have features of the intake structure S0 of the reference example, such as the offset portion 90, but it is also possible to not have this offset portion. For example, the tumble passage 64 of the intake structures S, S1 may be formed so as to be completely independent from the main passage 66 up to the junction 65 with the main passage 66. Furthermore, although the internal combustion engine 110 of the first and second embodiments of the present invention is equipped with a tumble valve 64c, the present invention can also be applied to an internal combustion engine that does not have a tumble valve, as shown in FIG. 1. [Explanation of symbols]

[0098] 14...cylinder head, 15...piston, 15a...top surface, 20...combustion chamber, 21...spark plug, 28...intake valve port, 30...exhaust valve port, 32...intake port, 38...intake passage, 46...intake valve, 50...exhaust valve, 64...tumble passage, 66...main passage, 100... combustion chamber ceiling surface, 100a... general surface, 100b... outer periphery, 101... spark plug hole, 102... recess, C...cylinder axis, C1...center point, C2...center point, CG...volume center of gravity, L...imaginary line.

Claims

1. a combustion chamber (20) defined by a cylinder head (14) and a top surface (15a) of a piston (15); a single intake valve (46) and a single exhaust valve (50) for opening and closing the combustion chamber (20); an intake valve port (28) opened and closed by the intake valve (46); and an exhaust valve port (30) opened and closed by the exhaust valve (50); an intake port (32) communicating with the intake valve port (28) and an exhaust port (34) communicating with the exhaust valve port (30), which are formed by extending from the intake valve port (28) and the exhaust valve port (30) while curving in directions away from each other; a tumble passage (64) that is arranged upstream of the intake port (32) and is partitioned by a partition portion (62), and a downstream deviation portion (90) is biased to one side with respect to an imaginary line (L) that connects a center point (C1) of the intake valve port (28) and a center point (C2) of the exhaust valve port (30); a spark plug (21) disposed on the side of the combustion chamber (20); The spark plug (21) is inserted into the spark plug hole (101) that opens to the one side, The tumble flow generated by the tumble passage (64) flows obliquely with respect to the imaginary line (L), The top surface (15a) of the piston (15) has a concave shape. The combustion chamber (20) has a ceiling surface (100) on the cylinder head (14) side, which has a recess (102). the recess (102) is disposed upstream of the spark plug (21) with respect to the inflow direction of the tumble flow, the recess (102) being oblique to the virtual line (L) and extending along the inflow direction of the tumble flow that flows along the combustion chamber ceiling surface (100); the recess (102) is provided continuously from an outer circumferential portion (100b) of the combustion chamber ceiling surface (100) in a region on the one side and on the intake valve (28) side toward the spark plug hole (101), so as to be continuous with the spark plug hole (101); The width of the recess (102) increases with increasing distance from the outer circumferential portion (100b), and is approximately the same width as the spark plug hole (101) in the vicinity of the spark plug hole (101).

2. 2. The internal combustion engine according to claim 1, wherein the recess (102) has a uniform cross-sectional area perpendicular to the direction of flow of the tumble flow that flows on the combustion chamber ceiling surface (100).

3. 2. The internal combustion engine according to claim 1, wherein a volume center of gravity (CG) of the combustion chamber (20) is located on the intake valve port (28) side and closer to a spark plug hole (101) into which the spark plug (21) is inserted, with respect to the imaginary line (L).

4. a combustion chamber (20) defined by a cylinder head (14) and a top surface (15a) of a piston (15); a single intake valve (46) and a single exhaust valve (50) for opening and closing the combustion chamber (20); an intake valve port (28) opened and closed by the intake valve (46); and an exhaust valve port (30) opened and closed by the exhaust valve (50); an intake port (32) communicating with the intake valve port (28); a first intake passage (64) and a second intake passage (66) disposed upstream of the intake port (32) for generating a tumble flow in the combustion chamber (20); a spark plug (21) disposed on the side of the combustion chamber (20); In the direction of the cylinder axis (C), when the combustion chamber (20) side is defined as an upper side and the piston (15) side is defined as a lower side, a second intake passage (66) is provided above the first intake passage (64) in an intake passage (38) connected to the combustion chamber (20) so as to overlap in the vertical direction, the first intake passage (64) curves downward in the direction of the cylinder axis (C) so as to move away from the second intake passage (66), a lower contour (64t) of the first intake passage (64) is formed so as to protrude downward from the upstream side toward the downstream side in the intake air flow direction, and extend upward after passing through a maximum downward protrusion (64u); a lower contour (64t) of the first intake passage (64) is tangent to a line (Ly) perpendicular to the cylinder axis (C); The first intake passage (64) is formed so as to be curved in a width direction perpendicular to the cylinder axis (C) and perpendicular to the intake / exhaust direction, The combustion chamber ceiling surface (100) on the cylinder head (14) side of the combustion chamber has a recess (102), The internal combustion engine is characterized in that the recess (102) is arranged upstream of the spark plug (21) with respect to the inflow direction of the tumble flow.

5. 5. The internal combustion engine according to claim 4, wherein the contour (64t) is tangent to the line (Ly) not at either end of the first intake passage (64) but at the maximum downward projection (64u).

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