internal combustion engine

Abstract

To provide an internal combustion engine which includes a chain case and enables the vibration and deformation thereof to be suppressed.SOLUTION: A chain case 20 has: a cylindrical intake-side cylinder portion 23 which swells to a crank shaft direction and in which an intake hydraulic control valve 15 is inserted; a cylindrical exhaust-side cylinder portion 24 which swells to the crank shaft direction and in which an exhaust hydraulic control valve 16 is inserted; and an intake-side fastening boss portion 25 and an exhaust-side fastening boss portion 26 which are disposed below a swelling portion 21 are used for mounting the chain case to a cylinder head 3. A lower portion of the swelling portion 21 is connected to an upper portion of the intake-side cylinder portion 23 and the exhaust-side cylinder portion 24. An upper portion of the intake-side fastening boss portion 25 is connected to a lower portion of the intake-side cylinder portion 23. An upper portion of the exhaust-side fastening boss portion 26 is connected to a lower portion of the exhaust-side cylinder portion 24.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an internal combustion engine. [Background technology]

[0002] In an internal combustion engine equipped with a variable valve timing mechanism, a technology is known in which a bulge that covers the variable valve timing mechanism is formed on the chain case (see Patent Document 1). The internal combustion engine described in Patent Document 1 is equipped with an oil control valve that controls the hydraulic oil to the variable valve timing mechanism, located below the bulge. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4340908 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the technology described in Patent Document 1, while the bulge portion occupies a large amount of internal space and surface area in the chain case, there are few points where the bulge portion is directly supported by the cylinder head, so there was a need to suppress vibration and deformation of the chain case due to insufficient rigidity of the bulge portion.

[0005] The present invention has been made in view of the above circumstances, and has as its object to provide an internal combustion engine that can suppress vibration and deformation of the chain case. [Means for solving the problem]

[0006] The present invention relates to an internal combustion engine including a variable valve timing mechanism around which a timing chain is wound, a hydraulic control valve that controls hydraulic oil supplied to the variable valve timing mechanism, and a chain case fixed to a cylinder head so as to cover the timing chain and the variable valve timing mechanism, wherein a bulging portion that bulges in the crankshaft direction and covers the variable valve timing mechanism is formed on the chain case, and the hydraulic control valve is disposed below the bulging portion, and the hydraulic control valve is composed of an intake hydraulic control valve and an exhaust hydraulic control valve, and the chain case has a cylindrical intake side cylinder portion that bulges in the crankshaft direction and into which the intake hydraulic control valve is inserted, and a cylindrical exhaust side cylinder portion that bulges in the crankshaft direction and into which the exhaust hydraulic control valve is inserted, and an intake side fastening boss portion and an exhaust side fastening boss portion that are disposed below the bulging portion and for attaching the chain case to the cylinder head, and teeth The lower part of the bulge contact and a lower part of the intake side cylinder part teeth The upper part of the intake side fastening boss contact and a lower part of the exhaust side cylinder part teeth The upper part of the exhaust side fastening boss portion contact It is characterized by being [Effects of the Invention]

[0007] As described above, according to the present invention, it is possible to provide an internal combustion engine that can suppress vibration and deformation of the chain case. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a front view of an internal combustion engine according to an embodiment of the present invention. [Figure 2] FIG. 2 is a side view of an internal combustion engine according to an embodiment of the present invention. [Figure 3] FIG. 3 is a perspective view of a cylinder head of an internal combustion engine according to one embodiment of the present invention. [Figure 4]FIG. 4 is a front view of a cylinder head of an internal combustion engine according to one embodiment of the present invention. [Figure 5] FIG. 5 is a side view of a cylinder head of an internal combustion engine according to one embodiment of the present invention. [Figure 6] 6 is a cross-sectional view taken along the line VI-VI in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] An internal combustion engine according to one embodiment of the present invention includes a variable valve timing mechanism around which a timing chain is wound, a hydraulic control valve that controls hydraulic oil supplied to the variable valve timing mechanism, and a chain case fixed to a cylinder head so as to cover the timing chain and the variable valve timing mechanism. The chain case has a bulge that bulges in the crankshaft direction and covers the variable valve timing mechanism, and the hydraulic control valve is disposed below the bulge. The hydraulic control valve is composed of an intake hydraulic control valve and an exhaust hydraulic control valve. The chain case has a cylindrical intake side cylinder section that bulges in the crankshaft direction and into which the intake hydraulic control valve is inserted, and a cylindrical exhaust side cylinder section that bulges in the crankshaft direction and into which the exhaust hydraulic control valve is inserted. The chain case also has intake side fastening bosses and exhaust side fastening bosses that are disposed below the bulge and are used to attach the chain case to the cylinder head. The lower parts of the bulge are connected to the upper parts of the intake side cylinder section and the exhaust side cylinder section, the upper part of the intake side fastening boss is connected to the lower part of the intake side cylinder section, and the upper part of the exhaust side fastening boss is connected to the lower part of the exhaust side cylinder section.

[0010] As a result, the internal combustion engine according to one embodiment of the present invention can suppress vibration and deformation of the chain case. [Example]

[0011] An internal combustion engine according to an embodiment of the present invention will now be described with reference to the drawings, in which: Figures 1 to 6 are diagrams showing an internal combustion engine according to an embodiment of the present invention.

[0012] 1 to 6, the up-down, front-rear, left-right directions are based on the state in which the internal combustion engine is removed from the vehicle and held upright with the cylinder head directly above the crankshaft. The front-rear direction is shown to coincide with the front-rear direction of the vehicle in which the internal combustion engine is mounted.

[0013] 1 and 2, an internal combustion engine 1 mounted on a vehicle includes a cylinder block 2. A crankshaft 2A is provided in the cylinder block 2, and the crankshaft 2A extends in the front-rear direction.

[0014] The cylinder block 2 has three cylinders (not shown) arranged in the front-to-rear direction, and the cylinders extend in the up-to-down direction. The internal combustion engine 1 of this embodiment is a front-engine, rear-wheel drive (FR) type engine mounted vertically. Note that the internal combustion engine 1 is not limited to an in-line engine, and may be, for example, a V-type engine, and the number of cylinders is not limited to three.

[0015] A cylinder head 3 is provided above the cylinder block 2. The cylinder head 3 has an intake port 3A (see FIG. 2) for taking in air, an exhaust port 3B (see FIG. 1) for discharging exhaust gas, and intake and exhaust valves (not shown). The intake port 3A opens into the right side wall of the cylinder head 3, and the exhaust port 3B opens into the left side wall of the cylinder head 3.

[0016] A cylinder head cover 4 is provided above the cylinder head 3. An oil pan 5 is provided below the cylinder block 2, and oil for lubricating the internal combustion engine 1 is stored in the oil pan 5.

[0017] The internal combustion engine 1 is installed below a floor panel of a vehicle (not shown). The cylinder block 2 is installed so that the center lines of the multiple cylinders are inclined relative to the vertical direction of the vehicle. More specifically, the cylinder block 2 is installed so that the center line is inclined left-right relative to the vertical direction, with its upper part located on the left and its lower part located on the right.

[0018] An undercover 1A is provided below the internal combustion engine 1. The undercover 1A extends horizontally and covers the internal combustion engine 1 from below. A bottom surface 5A of the oil pan 5 is located at the bottom of the internal combustion engine 1 when mounted on the vehicle. This bottom surface 5A is inclined with respect to the left-right direction of the internal combustion engine 1 itself so as to extend parallel to the undercover 1A when mounted on the vehicle.

[0019] In this way, the internal combustion engine 1 is mounted in a largely inclined position at the front of the vehicle. Therefore, when mounted on the vehicle, the right side (intake side) of the internal combustion engine 1 faces upward of the vehicle, and the left side (exhaust side) of the internal combustion engine 1 faces downward of the vehicle.

[0020] The internal combustion engine 1 includes a variable valve timing mechanism 11 around which a timing chain 10 is wound, a cylindrical intake hydraulic control valve 15 and an exhaust hydraulic control valve 16 as hydraulic control valves that control the hydraulic oil supplied to the variable valve timing mechanism 11, and a chain case 20 fixed to the cylinder head 3 so as to cover the timing chain 10 and the variable valve timing mechanism 11.

[0021] The variable valve timing mechanism 11 has an intake-side variable valve timing mechanism 12 that changes the opening and closing timing of the intake valve, and an exhaust-side variable valve timing mechanism 13 that changes the opening and closing timing of the exhaust valve.

[0022] The intake side variable valve timing mechanism 12 is disposed on the right side of the upper end of the cylinder head 3, and the exhaust side variable valve timing mechanism 13 is disposed on the left side of the upper end of the cylinder head 3.

[0023] The edge of the chain case 20 is fixed to the cylinder head 3 with multiple bolts. A bulge 21 is formed at the top of the chain case 20, and this bulge 21 bulges in the crankshaft direction (forward) and covers the variable valve timing mechanism 11. The intake hydraulic control valve 15 and the exhaust hydraulic control valve 16 are located below the bulge 21.

[0024] In this embodiment, the bulging portion 21 occupies a large amount of internal space and surface area in the chain case 20, but there are few locations where the bulging portion 21 is directly supported by the cylinder head 3. For this reason, it is desirable to improve the rigidity and strength of the chain case 20 so that the chain case 20 does not vibrate or deform due to insufficient rigidity of the bulging portion 21. Meanwhile, the internal combustion engine 1 of this embodiment is supported by the vehicle body at a location other than the chain case 20, and is therefore mounted on the vehicle in a significantly tilted position. For this reason, no mount attachment portions with increased strength for supporting the internal combustion engine 1 on the vehicle body are formed near the bulging portion 21 of the chain case 20. For this reason, it is desirable to ensure the rigidity and strength of the chain case 20 even without the formation of mount attachment portions.

[0025] Therefore, in this embodiment, the rigidity and strength of the bulge portion 21 of the chain case 20 and its surrounding areas are improved by the arrangement of the intake side cylinder portion 23 and the exhaust side cylinder portion 24 described below, and the connecting structure of each portion.

[0026] In Figures 3 and 4, the chain case 20 has a cylindrical intake side cylinder portion 23 that bulges in the crankshaft direction and into which the intake hydraulic control valve 15 is inserted, and a cylindrical exhaust side cylinder portion 24 that bulges in the crankshaft direction and into which the exhaust hydraulic control valve 16 is inserted.

[0027] The intake hydraulic control valve 15 and the exhaust hydraulic control valve 16 are inserted from the left (from above when mounted on the vehicle) into the intake-side cylinder portion 23 and the exhaust-side cylinder portion 24, respectively. Therefore, the insertion directions of the intake hydraulic control valve 15 and the exhaust hydraulic control valve 16 are the same, making the insertion work easier.

[0028] Furthermore, since the intake hydraulic control valve 15 and the exhaust hydraulic control valve 16 are positioned above the intake side cylinder section 23 and the exhaust side cylinder section 24 when mounted on the vehicle, even if foreign matter mixed in the hydraulic oil settles, the foreign matter can be prevented from entering the intake hydraulic control valve 15 and the exhaust hydraulic control valve 16.

[0029] The chain case 20 has an intake side fastening boss portion 25 and an exhaust side fastening boss portion 26 for attaching the chain case 20 to the cylinder head 3. The intake side fastening boss portion 25 and the exhaust side fastening boss portion 26 are disposed below the bulge portion 21.

[0030] The lower part of the bulge 21 is connected to the upper parts of the intake side cylinder 23 and the exhaust side cylinder 24. The upper part of the intake side fastening boss 25 is connected to the lower part of the intake side cylinder 23. The upper part of the exhaust side fastening boss 26 is connected to the lower part of the exhaust side cylinder 24.

[0031] The upper surface of the cylinder head 3 forms a joining surface to be joined to the cylinder head cover 4. The upper surface of the cylinder head 3 extends flatly in the front-rear and left-right directions.

[0032] The intake hydraulic control valve 15, the exhaust hydraulic control valve 16, the intake-side cylinder section 23, and the exhaust-side cylinder section 24 extend parallel to the upper surface of the cylinder head 3. The intake hydraulic control valve 15, the exhaust hydraulic control valve 16, the intake-side cylinder section 23, and the exhaust-side cylinder section 24 are also arranged side by side parallel to the upper surface of the cylinder head 3.

[0033] In other words, the intake hydraulic control valve 15, the exhaust hydraulic control valve 16, the intake side cylinder section 23, and the exhaust side cylinder section 24 are arranged in the chain case 20 in a position that extends in the left-right direction and is aligned in the left-right direction.

[0034] The intake side fastening boss portion 25 and the exhaust side fastening boss portion 26 are arranged side by side and parallel to the upper surface of the cylinder head 3. The intake side fastening boss portion 25 and the exhaust side fastening boss portion 26 are formed to protrude in the crankshaft direction (forward) beyond at least the intake side cylinder portion 23.

[0035] The intake-side cylinder section 23 and the exhaust-side cylinder section 24 are arranged side by side at different positions in the crankshaft direction. In other words, the intake-side cylinder section 23 and the exhaust-side cylinder section 24 are arranged side by side in the crankshaft direction. In this embodiment, the exhaust-side cylinder section 24 is arranged adjacent to and in front of the intake-side cylinder section 23.

[0036] Furthermore, when the chain case 20 is viewed along the crankshaft direction (see FIG. 3), the exhaust-side cylinder section 24 is positioned offset toward the exhaust side (left) relative to the intake-side cylinder section 23. In this embodiment, the exhaust-side cylinder section 24 is positioned adjacent to the left of the intake-side cylinder section 23. Thus, in this embodiment, the exhaust-side cylinder section 24 is positioned adjacent to the front and left of the intake-side cylinder section 23.

[0037] 3, 4, and 6, the chain case 20 has a cylindrical oil passage forming portion 27, which extends in a direction perpendicular to the crankshaft direction, passing through the lower part of the intake side fastening boss portion 25 and the lower part of the exhaust side fastening boss portion 26. An oil passage 27A through which hydraulic oil flows is formed inside the oil passage forming portion 27. The oil passage forming portion 27 is connected to the lower part of the intake side fastening boss portion 25 and the lower part of the exhaust side fastening boss portion 26.

[0038] The chain case 20 has a reinforcing rib 28 below the intake side cylinder portion 23, and the reinforcing rib 28 extends in the axial direction of the intake side cylinder portion 23. The reinforcing rib 28 connects the intake side cylinder portion 23, the exhaust side cylinder portion 24, and the intake side fastening boss portion 25.

[0039] Specifically, the reinforcing rib 28 extends in the axial direction of the intake-side cylinder section 23 along the lower part of the intake-side cylinder section 23, and the upper part of the reinforcing rib 28 is connected to the lower part of the intake-side cylinder section 23. The left end of the reinforcing rib 28 is connected to the lower part of the exhaust-side cylinder section 24. The lower part of the reinforcing rib 28 is connected to the upper part of the intake-side fastening boss section 25.

[0040] 3, 4, 5, and 6, the chain case 20 has a boss portion 34 at the bottom of the right end portion of the intake-side cylinder portion 23. The boss portion 34 is provided below the bulging portion 21. A leg portion 15A of the intake oil pressure control valve 15 is fastened to the boss portion 34. The leg portion 15A extends downward in the crankshaft direction (forward) at the left end portion of the intake oil pressure control valve 15.

[0041] The chain case 20 has a boss portion 35 at the top of the right end portion of the exhaust-side cylinder portion 24. The boss portion 35 is provided in the bulging portion 21. A leg portion 16A of the exhaust oil pressure control valve 16 is fastened to the boss portion 35. The leg portion 16A extends upward in the crankshaft direction (forward) at the left end portion of the exhaust oil pressure control valve 16.

[0042] An intake-side rib 31, a first exhaust-side rib 32, and a second exhaust-side rib 33 are formed on the surface of the chain case 20 so as to protrude in the crankshaft direction (forward). A boss portion 37 extending in the crankshaft direction (forward) is formed near the left end of the bulging portion 21 of the chain case 20. A boss portion 36 extending in the crankshaft direction (forward) is formed on the upper end of the chain case 20.

[0043] The intake side rib 31 is provided near the right end of the chain case 20. The intake side rib 31 extends diagonally downward and to the right from the boss portion 34 to the right end of the chain case 20 below the bulge portion 21. The intake side rib 31 reinforces the boss portion 34 by dispersing the load acting on the boss portion 34 toward the right end of the chain case 20.

[0044] The exhaust-side first rib 32 is provided near the left end of the bulge 21 of the chain case 20. The exhaust-side first rib 32 extends obliquely in an upper left direction from the left end of the exhaust-side cylinder 24 to the boss 37. The exhaust-side first rib 32 is connected to the left end of the exhaust-side cylinder 24 and the boss 37.

[0045] Therefore, the exhaust-side cylinder portion 24 and the boss portion 37 are connected by the exhaust-side first rib 32. As a result, the load acting on the exhaust-side cylinder portion 24 is distributed to the chain case 20 via the boss portion 37.

[0046] The exhaust-side second rib 33 is provided near the upper end of the chain case 20. The exhaust-side second rib 33 extends obliquely upward and to the right from the boss portion 35 to the boss portion 36. The exhaust-side second rib 33 is connected to the boss portion 35 and the boss portion 36. Therefore, the boss portion 35 and the boss portion 36 are connected by the exhaust-side second rib 33. As a result, the load acting on the boss portion 35 is distributed to the boss portion 36 via the exhaust-side second rib 33.

[0047] As described above, in this embodiment, the chain case 20 has a cylindrical intake-side cylinder portion 23 that bulges in the crankshaft direction and into which the intake hydraulic control valve 15 is inserted, and a cylindrical exhaust-side cylinder portion 24 that bulges in the crankshaft direction and into which the exhaust hydraulic control valve 16 is inserted. The chain case 20 also has an intake-side fastening boss portion 25 and an exhaust-side fastening boss portion 26 that are disposed below the bulging portion 21 and are used to attach the chain case 20 to the cylinder head 3. The lower portions of the bulging portion 21 are connected to the upper portions of the intake-side cylinder portion 23 and the exhaust-side cylinder portion 24, the upper portion of the intake-side fastening boss portion 25 is connected to the lower portion of the intake-side cylinder portion 23, and the upper portion of the exhaust-side fastening boss portion 26 is connected to the lower portion of the exhaust-side cylinder portion 24.

[0048] In this way, by connecting the lower part of the bulge portion 21 with the upper part of the cylindrical intake side cylinder portion 23 and the exhaust side cylinder portion 24, the bulge portion 21 can be reinforced by the intake side cylinder portion 23 and the exhaust side cylinder portion 24, and the rigidity of the bulge portion 21 can be improved.

[0049] In addition, since the intake side cylinder portion 23 and the exhaust side cylinder portion 24 are connected to the highly rigid intake side fastening boss portion 25 and the exhaust side fastening boss portion 26, respectively, the lower portions of the intake side cylinder portion 23 and the exhaust side cylinder portion 24 in the chain case 20 can be reinforced.

[0050] This makes it possible to suppress vibration and deformation of the chain case 20, particularly around the bulging portion 21. Furthermore, since the surface rigidity of the chain case 20 can be improved, noise emitted from the internal combustion engine 1 can be effectively blocked.

[0051] As a result, vibration and deformation of the chain case 20 can be suppressed.

[0052] In this embodiment, the intake side cylinder section 23 and the exhaust side cylinder section 24 are arranged side by side at different positions in the crankshaft direction.

[0053] This allows the intake side cylinder section 23 and the exhaust side cylinder section 24 to be reduced in size in the up-down direction compared to when the intake side cylinder section 23 and the exhaust side cylinder section 24 are positioned at the same position in the crankshaft direction, and the fastening boss section can be positioned closer to the cylinder head cover 4 above the chain case 20. Therefore, the bulge section 21 and the fastening boss section can be positioned closer to each other, and the bulge section 21, the cylinder section, and the fastening boss section can be firmly connected, which improves the rigidity of the chain case 20 and suppresses vibration and deformation of the chain case 20.

[0054] Furthermore, by arranging the intake side cylinder section 23 and the exhaust side cylinder section 24 in parallel, components such as the intake side cylinder section 23 and the exhaust side cylinder section 24 can be arranged compactly on the surface of the chain case 20, thereby avoiding the need to significantly change the arrangement of other components.

[0055] In addition, in this embodiment, when the chain case 20 is viewed along the crankshaft direction, the exhaust-side cylinder portion 24 is positioned more biased toward the exhaust side than the intake-side cylinder portion 23 .

[0056] As a result, a step is formed in the chain case 20 due to the exhaust side cylinder section 24 being positioned more toward the exhaust side than the intake side cylinder section 23, thereby improving the rigidity of the chain case 20 and suppressing vibration and deformation of the chain case 20.

[0057] Furthermore, by arranging the intake-side cylinder section 23 and the exhaust-side cylinder section 24 in a straight line below the bulge section 21, vibration of the bulge section 21 can be suppressed, improving the surface rigidity of the chain case 20. As a result, the chain case 20 can effectively block out noise radiated from the internal combustion engine 1.

[0058] In addition, in this embodiment, the chain case 20 has a reinforcing rib 28 below the intake side cylinder portion 23 that extends in the axial direction of the intake side cylinder portion 23, and the reinforcing rib 28 connects the intake side cylinder portion 23, the exhaust side cylinder portion 24, and the intake side fastening boss portion 25.

[0059] As a result, by connecting the intake-side cylinder portion 23, the exhaust-side cylinder portion 24, and the intake-side fastening boss portion 25 below the bulge portion 21 with the reinforcing rib 28, the lower portion of the bulge portion 21 can be more firmly reinforced. This makes it possible to suppress vibration and deformation around the bulge portion 21 of the chain case 20.

[0060] In addition, in this embodiment, the chain case 20 has a cylindrical oil passage forming portion 27 that extends in a direction perpendicular to the crankshaft direction, passing through the lower part of the intake side fastening boss portion 25 and the lower part of the exhaust side fastening boss portion 26, and the oil passage forming portion 27 is connected to the lower part of the intake side fastening boss portion 25 and the lower part of the exhaust side fastening boss portion 26.

[0061] As a result, the cylindrical, highly rigid oil passage forming portion 27 is connected to the lower part of the intake-side fastening boss portion 25 and the lower part of the exhaust-side fastening boss portion 26 below the bulge portion 21, thereby reinforcing the area of ​​the chain case 20 near the lower part of the bulge portion 21 and improving surface rigidity. This makes it possible to suppress vibration and deformation of the area of ​​the chain case 20 near the lower part of the bulge portion 21. Furthermore, by improving the surface rigidity of the chain case 20, the chain case 20 can effectively block out noise radiated from the internal combustion engine 1.

[0062] While an embodiment of the present invention has been disclosed, it will be apparent to one skilled in the art that modifications may be made thereto without departing from the scope of the present invention, and it is intended that all such modifications and equivalents be included in the following claims. [Explanation of symbols]

[0063] 1...internal combustion engine, 3...cylinder head, 10...timing chain, 11...variable valve timing mechanism, 15...intake hydraulic control valve, 16...exhaust hydraulic control valve, 20...chain case, 21...bulge portion, 23...intake side cylinder portion, 24...exhaust side cylinder portion, 25...intake side fastening boss portion, 26...exhaust side fastening boss portion, 27...oil passage forming portion, 28...reinforcing rib

Claims

1. A variable valve timing mechanism with a timing chain wrapped around it, a hydraulic control valve for controlling hydraulic oil supplied to the variable valve timing mechanism; a chain case fixed to the cylinder head so as to cover the timing chain and the variable valve timing mechanism, a bulging portion that bulges in the crankshaft direction and covers the variable valve timing mechanism is formed on the chain case; The internal combustion engine has the hydraulic control valve disposed below the bulging portion, the hydraulic control valve is composed of an intake hydraulic control valve and an exhaust hydraulic control valve, The chain case is an intake-side cylinder portion bulging in the crankshaft direction and into which the intake hydraulic control valve is inserted; a cylindrical exhaust-side cylinder portion that bulges in the crankshaft direction and into which the exhaust oil pressure control valve is inserted; an intake side fastening boss portion and an exhaust side fastening boss portion disposed below the bulging portion for attaching the chain case to the cylinder head, a lower portion of the bulging portion is connected to an upper portion of the intake side cylinder portion and an upper portion of the exhaust side cylinder portion; an upper portion of the intake side fastening boss portion is connected to a lower portion of the intake side cylinder portion; an upper portion of the exhaust-side fastening boss portion connected to a lower portion of the exhaust-side cylinder portion;

2. 2. The internal combustion engine according to claim 1, wherein the intake-side cylinder portion and the exhaust-side cylinder portion are arranged side by side at different positions in the crankshaft direction.

3. 3. An internal combustion engine according to claim 1, wherein, when the chain case is viewed along the crankshaft direction, the exhaust-side cylinder portion is positioned more toward the exhaust side than the intake-side cylinder portion.

4. the chain case has a reinforcing rib below the intake side cylinder portion, the reinforcing rib extending in the axial direction of the intake side cylinder portion, 4. The internal combustion engine according to claim 1, wherein the reinforcing rib connects the intake-side cylinder portion, the exhaust-side cylinder portion, and the intake-side fastening boss portion.

5. the chain case has a cylindrical oil passage forming portion that passes through a lower portion of the intake side fastening boss portion and a lower portion of the exhaust side fastening boss portion and extends in a direction perpendicular to the crankshaft direction, 5. The internal combustion engine according to claim 1, wherein the oil passage forming portion is connected to a lower portion of the intake side fastening boss portion and a lower portion of the exhaust side fastening boss portion.

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