INTERNAL COMBUSTION ENGINE AND STRADDLED VEHICLE HAVING THE SAME

Abstract

 As viewed along a cylinder axial line CA so that a center 51C of a first intake opening 51A is located leftward and upward of the cylinder axial line CA, an axial line 55C of a plug hole 55 is inclined relative to the cylinder axial line CA so as to diverge leftward of the cylinder axial line CA while extending away from an ignition opening 55A along the cylinder axial line CA. The plug hole 55 is located between a first intake port 51 and a first exhaust port 61. A water jacket 10A includes a middle passage 30 including an inter-port passage 31 that is located between the first exhaust port 61 and a second exhaust port 62 and downward of the cylinder axial line CA, and an extension passage 32 extending upward from the inter-port passage 31 to a position that is upward of the cylinder axial line CA.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to an internal combustion engine including a water jacket, and a straddled vehicle having the same.

Description of the Related Art

[0002] For example, a 4-valve water-cooled internal combustion engine includes a cylinder body having a cylinder, and a cylinder head having two intake ports and two exhaust ports. A water jacket, which provides a passage for the coolant, is formed on the cylinder body and the cylinder head.

[0003] A portion of the cylinder head between two exhaust ports is likely to be hot. Japanese Laid-Open Patent Publication No. 2015-010598 discloses an internal combustion engine in which a passage for the coolant is provided between two exhaust ports in order to suppress the increase in temperature in the portion between the exhaust ports.

[0004] In the internal combustion engine disclosed in Japanese Laid-Open Patent Publication No. 2015-010598, the ignition plug is arranged so that the axial line of the ignition plug and the axial line of the cylinder coincide with each other. The axial line of the plug hole accommodating the ignition plug therein coincides with the cylinder axial line. However, in the cylinder head, the area between the plug hole and the exhaust port is small. By simply forming a passage in the portion between exhaust ports, only a small passage can be formed. Japanese Laid-Open Patent Publication No. 2018-155215 discloses an internal combustion engine in which a plug hole is provided between two intake ports, and the axial line of the plug hole is inclined relative to the cylinder axial line so that the axial line extends toward the intake ports away from the combustion chamber. With the internal combustion engine, the area between the plug hole and the exhaust ports can be made large. Thus, it is possible to enlarge the passage between exhaust ports.

SUMMARY OF THE INVENTION

[0005] However, with the internal combustion engine disclosed in Japanese Laid-Open Patent Publication No. 2018-155215, the coolant tends not to flow smoothly through the passage between exhaust ports.

[0006] The present invention has been made in view of the above, and an object thereof is to provide an internal combustion engine that is capable of effectively cooling a portion of the cylinder head between exhaust ports, and a straddled vehicle having the same.

[0007] An internal combustion engine disclosed herein includes a cylinder body, a cylinder head, a first intake port, a second intake port, a first exhaust port, a second exhaust port, a plug hole, and a water jacket. The cylinder body includes a cylinder formed therein that extends along a cylinder axial line and defines a portion of a combustion chamber. The cylinder head is secured on the cylinder body. The first intake port is formed on the cylinder head and includes a first intake opening facing toward the combustion chamber. An intake air to be taken into the combustion chamber flows through the first intake port. The second intake port is formed on the cylinder head and includes a second intake opening facing toward the combustion chamber. An intake air to be taken into the combustion chamber flows through the second intake port. The first exhaust port is formed on the cylinder head and includes a first exhaust opening facing toward the combustion chamber. An exhaust air to be exhausted from the combustion chamber flows through the first exhaust port. The second exhaust port is formed on the cylinder head and includes a second exhaust opening facing toward the combustion chamber. An exhaust air to be exhausted from the combustion chamber flows through the second exhaust port. The plug hole is formed on the cylinder head and includes an ignition opening facing toward the combustion chamber. An ignition plug is accommodated in the plug hole. The water jacket is formed on the cylinder head. A coolant flows through the water jacket. As viewed along the cylinder axial line so that a center of the first intake opening is located leftward and upward of the cylinder axial line, a center of the second intake opening is located rightward and upward of the cylinder axial line, a center of the first exhaust opening is located leftward and downward of the cylinder axial line, and a center of the second exhaust opening is located rightward and downward of the cylinder axial line. As viewed as described above, an axial line of the plug hole is inclined relative to the cylinder axial line so as to diverge leftward of the cylinder axial line while extending away from the ignition opening along the cylinder axial line. As viewed as described above, the plug hole is located between the first intake port and the first exhaust port. As viewed as described above, the water jacket includes a middle passage, wherein the middle passage includes an inter-port passage that is located between the first exhaust port and the second exhaust port and downward of the cylinder axial line, and an extension passage that extends upward from the inter-port passage to a position that is upward of the cylinder axial line.

[0008] With the internal combustion engine described above, since the plug hole is inclined from the cylinder axial line, the area between the first exhaust port and the second exhaust port can be made large. Therefore, it is possible to ensure a sufficient size of the inter-port passage. The plug hole is provided between the first intake port and the first exhaust port. Therefore, it is possible to ensure a sufficient area where a passage can be formed between the first intake port and the second intake port. The extension passage extending from the inter-port passage is provided in this area. Thus, the coolant having flown through the inter-port passage can continue to flow straight through the extension passage. Therefore, it is possible to smooth the coolant flow through the inter-port passage. Therefore, it is possible to effectively cool the portion of the cylinder head between the first exhaust port and the second exhaust port.

[0009] According to one preferred aspect, as viewed along the cylinder axial line so that the center of the first intake opening is located leftward and upward of the cylinder axial line, the water jacket includes a first right passage that is located rightward and downward relative to a center of the second exhaust port, a second right passage that is located upward relative to the center of the second exhaust port and is connected to the first right passage and the middle passage, and a third right passage that is located upward relative to the second right passage and downward relative to a center of the second intake port and is connected to the middle passage. The second right passage and the third right passage are partitioned from each other in an up-down direction in a portion that is leftward relative to the center of the second intake opening and the center of the second exhaust opening.

[0010] According to this aspect, the coolant having flown through the second right passage flows into the third right passage via the middle passage. The second right passage and the third right passage are partitioned from each other in the up-down direction in the portion that is leftward relative to the center of the second intake opening and the center of the second exhaust opening. Therefore, the coolant having flown through the second right passage merges with the coolant flowing through the middle passage after flowing to a point that is leftward relative to the center of the second exhaust opening. Thus, the coolant in the second right passage and the coolant in the middle passage can be merged together without significantly hindering the straight flow of the coolant through the inter-port passage and the extension passage. Therefore, it is possible to further smooth the coolant flow through the inter-port passage. It is also possible to effectively cool the portion around the second exhaust port.

[0011] According to one preferred aspect, along a predetermined section that is parallel to a straight line that connects together the center of the first exhaust opening and the center of the second exhaust opening and is parallel to the cylinder axial line, a ratio of a dimension of the inter-port passage in a direction that is parallel to the cylinder axial line to a dimension thereof in a direction that is perpendicular to the cylinder axial line is greater than 1.

[0012] In the cylinder head, the dimension between the first exhaust port and the second exhaust port is relatively small. According to this aspect, however, along the section, the dimension of the inter-port passage in a direction parallel to the cylinder axial line is greater than the dimension thereof in a direction perpendicular to the cylinder axial line (i.e., the dimension between the first exhaust port and the second exhaust port). Therefore, it is possible to ensure a sufficient passage cross-sectional area of the inter-port passage. Therefore, it is possible to effectively cool the portion of the cylinder head between the first exhaust port and the second exhaust port.

[0013] According to one preferred aspect, along the predetermined section, the inter-port passage has a side that is parallel to the cylinder axial line.

[0014] According to this aspect, it is possible to effectively cool the portion of the cylinder head between the first exhaust port and the second exhaust port.

[0015] According to one preferred aspect, as viewed along the cylinder axial line so that the center of the first intake opening is located leftward and upward of the cylinder axial line, the water jacket includes a first left passage that is located downward relative to a center of the first exhaust port, a second left passage that is located leftward and upward relative to the center of the first exhaust port and is connected to the first left passage, and a third left passage that is located leftward and downward relative to a center of the first intake port and is connected to the second left passage.

[0016] According to this aspect, it is possible to effectively cool the portion leftward of the first exhaust port.

[0017] According to one preferred aspect, the extension passage and the second left passage are not directly connected to each other, and the extension passage and the third left passage are not directly connected to each other.

[0018] If the extension passage is directly connected to the second left passage or the third left passage, there is formed a passage that extends in the left-right direction from the second right passage or the third right passage to the second left passage or the third left passage, and such a passage will be substantially orthogonal to the inter-port passage. In that case, the coolant flow through the inter-port passage is likely to be disturbed by the coolant flow through the substantially orthogonal passage. As a result, it may be more difficult for the coolant to flow smoothly through the inter-port passage. According to this aspect, however, the extension passage is not directly connected to either the second left passage or the third left passage. Thus, the coolant can smoothly flow through the inter-port passage. Therefore, it is possible to effectively cool the portion of the cylinder head between the first exhaust port and the second exhaust port.

[0019] According to one preferred aspect, as viewed along the cylinder axial line so that the center of the first intake opening is located leftward and upward of the cylinder axial line, the second left passage extends rightward and upward toward the third left passage, and the third left passage extends rightward and downward toward the second left passage.

[0020] According to this aspect, it is possible to effectively cool the portion around the first exhaust port.

[0021] According to one preferred aspect, along a predetermined section that is parallel to a straight line that connects together the center of the first exhaust opening and the center of the second exhaust opening and is parallel to the cylinder axial line, a ratio of a dimension of the inter-port passage in a direction that is parallel to the cylinder axial line to a dimension thereof in a direction that is perpendicular to the cylinder axial line is greater than the ratio for the first right passage and is greater than the ratio for the first left passage.

[0022] In the cylinder head, the dimension between the first exhaust port and the second exhaust port is relatively small. According to this aspect, along the section, however, the ratio of the dimension of the inter-port passage in a direction parallel to the cylinder axial line to the dimension thereof in a direction perpendicular to the cylinder axial line (i.e., the dimension between the first exhaust port and the second exhaust port) is large. Therefore, it is possible to ensure a sufficient passage cross-sectional area of the inter-port passage. Therefore, it is possible to effectively cool the portion of the cylinder head between the first exhaust port and the second exhaust port.

[0023] As viewed along the cylinder axial line so that the center of the first intake opening is located leftward and upward of the cylinder axial line, the water jacket may include an inlet opening that is located rightward and downward relative to the second exhaust opening, wherein the coolant flows in through the inlet opening.

[0024] As viewed along the cylinder axial line so that the center of the first intake opening is located leftward and upward of the cylinder axial line, the water jacket may include an inlet opening that is located rightward and downward relative to the second exhaust opening, wherein the coolant flows in through the inlet opening, and the first left passage may include a diameter-constricted portion that constricts the coolant flow.

[0025] When the inlet opening is provided rightward and downward relative to the second exhaust opening, the coolant that has flown in through the inlet opening tends to flow leftward and upward. According to this aspect, the first left passage includes the diameter-constricted portion that constricts the coolant flow. Therefore, the coolant is prevented from excessively flowing into the first left passage. A sufficient amount of the coolant flows into the inter-port passage. Therefore, it is possible to effectively cool the portion of the cylinder head between the first exhaust port and the second exhaust port.

[0026] The internal combustion engine may include an inlet opening for guiding the coolant from an outside of the internal combustion engine to an inside of the internal combustion engine, and the inlet opening may be formed on the cylinder head.

[0027] The internal combustion engine may include an inlet opening for guiding the coolant from an outside of the internal combustion engine to an inside of the internal combustion engine and an exit opening for guiding the coolant to the outside of the internal combustion engine, and the inlet opening and the exit opening may be formed on the cylinder head.

[0028] According to one preferred aspect, the internal combustion engine includes a camshaft that is rotatably supported on the cylinder head and crosses the cylinder axial line. An axial line of the camshaft is located between the center of the first intake opening and the center of the first exhaust opening and is located between the center of the second intake opening and the center of the second exhaust opening.

[0029] Since the plug hole is inclined relative to the cylinder axial line, it is possible to ensure a sufficient space for arranging the camshaft that crosses the cylinder axial line and extends in the left-right direction without increasing the size of the cylinder head, as viewed along the cylinder axial line as described above. Therefore, it is possible to reduce the size of the cylinder head.

[0030] According to one preferred aspect, the cylinder head is a cast product.

[0031] According to this aspect, it is possible to relatively easily form the water jacket configured as described above.

[0032] A straddled vehicle disclosed herein includes the internal combustion engine as set forth above.

[0033] According to the present invention, it is possible to provide an internal combustion engine that is capable of effectively cooling a portion of the cylinder head between exhaust ports, and a straddled vehicle having the same.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] 

FIG. 1 is a side view of a motorcycle according to an embodiment.

FIG. 2 is a view of a portion of an internal combustion engine according to an embodiment, as viewed along the cylinder axial line.

FIG. 3 is a cross-sectional view taken along line III-III of FIG. 2.

FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 2.

FIG. 5 is a cross-sectional view taken along line V-V of FIG. 2.

FIG. 6 is a cross-sectional view taken along line VI-VI of FIG. 2.

FIG. 7 is a bottom view of a cylinder head.

FIG. 8 is a view showing walls of a water jacket of the cylinder head.

FIG. 9 is a cross-sectional view of the water jacket of the cylinder head taken in a plane perpendicular to the cylinder axial line.

FIG. 10 is an end view taken along line X-X of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] An embodiment will now be described with reference to the drawings. FIG. 1 is a motorcycle 100 according to the present embodiment. The motorcycle 100 is an example of the straddled vehicle. A straddled vehicle refers to a vehicle that is straddled by a passenger. A straddled vehicle is not limited to the motorcycle 100. A straddled vehicle may be an auto tricycle, an ATV (All Terrain Vehicle), or the like.

[0036] The motorcycle 100 includes a body frame 102 having a head pipe 101, a seat 103 supported on the body frame 102, an internal combustion engine (hereinafter referred to as an engine) 1 supported on the body frame 102, a handle 104 pivotally supported on the head pipe 101, a front wheel 105, and a rear wheel 106 driven by the engine 1.

[0037] The engine 1 is a 4-stroke water-cooled engine. The engine 1 includes a crankcase 2 accommodating a crankshaft (not shown) therein, a cylinder body 3 secured on the crankcase 2 (see FIG. 3), a cylinder head 4 secured on the cylinder body 3, and a cylinder head cover 5 secured on the cylinder head 4. FIG. 2 is a view of a portion of the engine 1 as viewed along the cylinder axial line CA (see FIG. 4). FIG. 3 is a cross-sectional view taken along line III-III of FIG. 2. FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 2. FIG. 5 is a cross-sectional view taken along line V-V of FIG. 2. FIG. 6 is a cross-sectional view taken along line VI-VI of FIG. 2. Note that although the cylinder axial line CA does not exist on the cross sections shown in FIG. 3 and FIG. 5, the cylinder axial line CA is drawn at the center of a cylinder 6 also in FIG. 3 and FIG. 5 for the purpose of illustration.

[0038] As shown in FIG. 4, the cylinder body 3 includes the cylinder 6 formed therein. The cylinder 6 extends along the cylinder axial line CA. A piston 7 is accommodated inside the cylinder 6. The cylinder 6 defines a portion of a combustion chamber 8. The piston 7 is linked to the crankshaft via a connected rod (not shown).

[0039] FIG. 7 is a bottom view of the cylinder head 4. The cylinder head 4 is formed with a first intake port 51, a second intake port 52, a first exhaust port 61 and a second exhaust port 62. The first intake port 51, the second intake port 52, the first exhaust port 61 and the second exhaust port 62 have a first intake opening 51A, a second intake opening 52A, a first exhaust opening 61A and a second exhaust opening 62A, respectively, facing toward the combustion chamber 8. The intake air to be sucked into the combustion chamber 8 flows through the first intake port 51 and the second intake port 52. The exhaust air to be exhausted from the combustion chamber 8 flows through the first exhaust port 61 and the second exhaust port 62. The cylinder head 4 is formed with a plug hole 55 that accommodates an ignition plug 50 therein. The plug hole 55 has an ignition opening 55A facing toward the combustion chamber 8. The cylinder head 4 is a cast product. The cylinder head 4 is produced by casting.

[0040] As shown in FIG. 3, the engine 1 includes a first intake valve 53 that opens/closes the first intake opening 51A, and a first exhaust valve 63 that opens/closes the first exhaust opening 61A. As shown in FIG. 5, the engine 1 includes a second intake valve 54 that opens/closes the second intake opening 52A, and a second exhaust valve 64 that opens/closes the second exhaust opening 62A. The engine 1 includes a camshaft 57 that is rotatably supported on the cylinder head 4. As shown in FIG. 4, the camshaft 57 crosses the cylinder axial line CA. As shown in FIG. 3, the axial line 57C of the camshaft 57 is located between the center of the first intake opening 51A and the center of the first exhaust opening 61A. As shown in FIG. 5, the axial line 57C of the camshaft 57 is located between the center of the second intake opening 52A and the center of the second exhaust opening 62A. The first intake valve 53, the second intake valve 54, the first exhaust valve 63 and the second exhaust valve 64 are engaged with the camshaft 57 via a rocker arm 58. The first intake valve 53, the second intake valve 54, the first exhaust valve 63 and the second exhaust valve 64 are opened/closed following the rotation of the camshaft 57.

[0041] The engine 1 is formed with a water jacket 10 through which the coolant flows (see FIG. 5). The water jacket 10 includes a water jacket 10A formed on the cylinder head 4, and a water jacket 10B formed on the cylinder body 3.

[0042] FIG. 8 is a view showing walls of the water jacket 10A of the cylinder head 4, showing the water jacket 10A as viewed from the cylinder head cover 5 along the cylinder axial line CA. Note that the walls are extracted from the cylinder head 4 in FIG. 8. As viewed along the cylinder axial line CA so that the center 51C of the first intake opening 51A is located leftward and upward of the cylinder axial line CA as shown in FIG. 8, the center 52C of the second intake opening 52A is located rightward and upward of the cylinder axial line CA, the center 61C of the first exhaust opening 61A is located leftward and downward of the cylinder axial line CA, and the center 62C of the second exhaust opening 62A is located rightward and downward of the cylinder axial line CA. The terms front, rear, left, right, up and down, as used in the description below, refer to these directions as viewed along the cylinder axial line CA so that the center 51C of the first intake opening 51A is located leftward and upward of the cylinder axial line CA, as shown in FIG. 8, unless specified otherwise.

[0043] As shown in FIG. 6, the axial line 55C of the plug hole 55 is inclined relative to the cylinder axial line CA so as to diverge leftward of the cylinder axial line CA while extending away from the ignition opening 55A (i.e., upward in FIG. 6) along the cylinder axial line CA. The plug hole 55 is located between the first intake port 51 and the first exhaust port 61.

[0044] FIG. 9 is a cross-sectional view of the water jacket 10A taken along a direction perpendicular to the cylinder axial line CA. The water jacket 10A includes an inlet opening 11 through which the coolant flows in, an inlet passage 13, a right passage 20, a middle passage 30, a left passage 40, an exit passage 14, and an exit opening 12 through which the coolant flows out.

[0045] The inlet opening 11 is an opening for guiding the coolant into the water jacket 10 of the engine 1. The exit opening 12 is an opening for guiding the coolant out of the water jacket 10 of the engine 1. That is, the inlet opening 11 is an opening for guiding the coolant from the outside to the inside of the engine 1, and the exit opening 12 is an opening for guiding the coolant from the inside to the outside of the engine 1. The inlet opening 11 and the exit opening 12 are formed on the cylinder head 4. The inlet opening 11 is located rightward and downward relative to the center 62C of the second exhaust opening 62A. The inlet opening 11 is facing rightward. The exit opening 12 is located leftward and upward relative to the center 51C of the first intake opening 51A. The exit opening 12 is facing leftward.

[0046] The right passage 20 includes a first right passage 21 that is located rightward and downward relative to the center 62D of the second exhaust port 62, a second right passage 22 that is located upward relative to the center 62D of the second exhaust port 62, a third right passage 23 that is located upward relative to the second right passage 22 and downward relative to the center 52D of the second intake port 52, and a fourth right passage 24 that is located upward relative to the center 52D of the second intake port 52. The first right passage 21 is connected to the inlet passage 13. The second right passage 22 is connected to the first right passage 21 and the middle passage 30. The third right passage 23 is connected to the middle passage 30. The fourth right passage 24 is connected to the third right passage 23 and the exit passage 14. The second right passage 22 and the third right passage 23 are partitioned from each other in the up-down direction in the portion that is leftward relative to the center 52C of the second intake opening 52A and the center 62C of the second exhaust opening 62A.

[0047] The middle passage 30 includes an inter-port passage 31 and an extension passage 32. The inter-port passage 31 is formed between the first exhaust port 61 and the second exhaust port 62. The inter-port passage 31 is located downward of the cylinder axial line CA. The extension passage 32 extends upward from the inter-port passage 31 to a position that is upward of the cylinder axial line CA. The inter-port passage 31 and the extension passage 32 extend straight upward. The inter-port passage 31 is connected to the inlet passage 13 and the first right passage 21. The extension passage 32 is connected to the second right passage 22 and the third right passage 23.

[0048] The left passage 40 includes a first left passage 41 that is located downward relative to the center 61D of the first exhaust port 61, a second left passage 42 that is located leftward and upward relative to the center 61D of the first exhaust port 61, a third left passage 43 that is located leftward and downward relative to the center 51D of the first intake port 51, and a fourth left passage 44 that is located leftward and upward relative to the center 51D of the first intake port 51. The first left passage 41 is connected to the inlet passage 13 and the inter-port passage 31. The second left passage 42 is connected to the first left passage 41. The third left passage 43 is connected to the second left passage 42. The fourth left passage 44 is connected to the third left passage 43 and the exit passage 14. The second left passage 42 extends rightward and upward toward the third left passage 43. The third left passage 43 extends rightward and downward toward the second left passage 42. The first left passage 41 includes a diameter-constricted portion 46 that constricts the coolant flow. The passage cross-sectional area of the diameter-constricted portion 46 is smaller than that on the upstream side (the right side in FIG. 9) of the diameter-constricted portion 46 and that on the downstream side (the left side in FIG. 9).

[0049] As shown in FIG. 9, the extension passage 32 and the second left passage 42 are not directly connected to each other. The extension passage 32 and the third left passage 43 are not directly connected to each other. There is no passage through which the coolant passes between the first intake port 51 and the first exhaust port 61.

[0050] In the present embodiment, the exit passage 14 is provided around a hole 18 through which a bolt (not shown) is inserted. However, the hole 18 may not be necessary. There is no limitation on the shape of the exit passage 14 as long as the exit passage 14 is a passage that connects the fourth right passage 24 and the fourth left passage 44 to the exit opening 12.

[0051] FIG. 10 is an end view taken along line X-X of FIG. 8. That is, FIG. 10 is an end view taken along a predetermined section that is parallel to a straight line that connects together the center 61C of the first exhaust opening 61A and the center 62C of the second exhaust opening 62A and is parallel to the cylinder axial line CA. As shown in FIG. 10, the inter-port passage 31 is vertically elongated along the section. In FIG. 10, the X direction represents a direction that is perpendicular to the cylinder axial line CA. The Y direction represents a direction that is parallel to the cylinder axial line CA. Along the section, the dimension Ly of the inter-port passage 31 in the Y direction relative to the dimension Lx thereof in the X direction is greater than 1. Ly/Lx > 1. While there is no particular limitation on the value of Ly/Lx, Ly/Lx = 2 to 4, for example.

[0052] As shown in FIG. 10, along the section, the inter-port passage 31 is formed substantially in a rectangular shape. Along the section, the inter-port passage 31 has sides 31a that are parallel to the cylinder axial line CA. Note however that the shape shown in FIG. 10 is merely an example, and the shape of the inter-port passage 31 along the section is not limited to a rectangular shape.

[0053] As shown in FIG. 10, along the section, the dimensions of the first right passage 21 in the X direction and the Y direction are denoted as LRx and LRy, respectively. Along the section, the dimensions of the first left passage 41 in the X direction and the Y direction are denoted as LLx and LLy, respectively. Then, Ly/Lx is greater than LRy/LRx and greater than LLy/LLx. That is, along the section, the ratio of the dimension of the inter-port passage 31 in a direction parallel to the cylinder axial line CA to the dimension thereof in a direction perpendicular to the cylinder axial line CA is greater than that for the first right passage 21 and greater than that for the first left passage 41. Along the section, the inter-port passage 31 is more vertically elongated than the first right passage 21 and the first left passage 41.

[0054] As shown in FIG. 3 to FIG. 6, the water jacket 10B of the cylinder body 3 is formed around the cylinder 6. As shown in FIG. 7, the water jacket 10A of the cylinder head 4 has a plurality of holes 4a that are facing toward the water jacket 10B of the cylinder body 3. A gasket 9 (see FIG. 6) is interposed between the cylinder body 3 and the cylinder head 4. The gasket 9 also has a plurality of holes (not shown) similar to the holes 4a of the water jacket 10A of the cylinder head 4. In the present embodiment, the inlet opening 11 for guiding the coolant from the outside of the engine 1 and the exit opening 12 for guiding the coolant to the inside of the engine 1 are both provided on the cylinder head 4. Therefore, a portion of the coolant flowing in through the inlet opening 11 flows through the water jacket 10A of the cylinder head 4, the water jacket 10B of the cylinder body 3 and the water jacket 10A of the cylinder head 4, in this order, and flows out through the exit opening 12. Specifically, a portion of the coolant in the water jacket 10A of the cylinder head 4 flows into the water jacket 10B of the cylinder body 3 through two or more of the plurality of holes 4a. The coolant of the water jacket 10B of the cylinder body 3 flows into the water jacket 10A of the cylinder head 4 through other ones of the plurality of holes 4a.

[0055] Next, referring to FIG. 9, the flow of the coolant through the water jacket 10A of the cylinder head 4 will be described. The coolant that has flown into the inlet passage 13 through the inlet opening 11 branches into the first right passage 21, the inter-port passage 31 and the first left passage 41. The inlet opening 11 is located rightward and downward of the second exhaust opening 62A, and the coolant tends to flow leftward and upward in the inlet passage 13. Therefore, the coolant is prevented from excessively flowing into the first right passage 21. The first left passage 41 includes the diameter-constricted portion 46 that constricts the coolant flow. Therefore, the coolant is prevented from excessively flowing into the first left passage 41. Therefore, a sufficient amount of the coolant flows into the inter-port passage 31. The coolant flowing through the right passage 20, the coolant flowing through the middle passage 30 and the coolant flowing through the left passage 40 will be relatively even.

[0056] In the engine 1, a hot exhaust gas flows through the first exhaust port 61 and the second exhaust port 62. A portion of the cylinder head 4 between the first exhaust port 61 and the second exhaust port 62 is likely to be hot. However, the inter-port passage 31 is formed between the first exhaust port 61 and the second exhaust port 62. The portion between the first exhaust port 61 and the second exhaust port 62 is sufficiently cooled by the coolant flowing through the inter-port passage 31. Therefore, it is possible to effectively suppress the increase in temperature of the cylinder head 4.

[0057] In the present embodiment, the middle passage 30 includes the extension passage 32 extending upward from the inter-port passage 31. The coolant having flown through the inter-port passage 31 can continue to flow straight through the extension passage 32. In the present embodiment, there is no wall that blocks the coolant having flown through the inter-port passage 31. That is, in the water jacket 10A, there is no wall that extends in the left-right direction in the vicinity of the cylinder axial line CA. Therefore, it is possible to smooth the coolant flow through the inter-port passage 31, and to increase the flow rate of the coolant through the inter-port passage 31. Thus, it is possible to effectively cool the portion of the cylinder head 4 between the first exhaust port 61 and the second exhaust port 62.

[0058] The coolant having flown through the first right passage 21 flows through the second right passage 22 and then merges with the coolant in the middle passage 30. After merging, the coolant flows through the third right passage 23 and the fourth right passage 24. The coolant having flown through the first left passage 41 flows through the second left passage 42, the third left passage 43 and the fourth left passage 44 in this order. Then, the coolant in the fourth right passage 24 and the coolant in the fourth left passage 44 merge together in the exit passage 14 and flow out through the exit opening 12.

[0059] As described above, with the engine 1 according to the present embodiment, since the plug hole 55 is inclined from the cylinder axial line CA (see FIG. 6), the area of the cylinder head 4 between the first exhaust port 61 and the second exhaust port 62 can be made large. Therefore, it is possible to ensure a sufficient size of the inter-port passage 31 (see FIG. 4). The plug hole 55 is provided between the first intake port 51 and the first exhaust port 61 (see FIG. 8). Therefore, it is possible to ensure a sufficient area where a passage can be formed between the first intake port 51 and the second intake port 52. The extension passage 32 extending from the inter-port passage 31 is provided in this area (see FIG. 4 and FIG. 9). Thus, the coolant having flown through the inter-port passage 31 can continue to flow straight through the extension passage 32. The coolant is not blocked immediately after flowing out of the inter-port passage 31. Therefore, it is possible to smooth the coolant flow through the inter-port passage 31. According to the present embodiment, it is possible to effectively cool the portion of the cylinder head 4 between the first exhaust port 61 and the second exhaust port 62.

[0060] According to the present embodiment, the coolant having flown through the second right passage 22 flows into the third right passage 23 via the middle passage 30. The second right passage 22 and the third right passage 23 are partitioned from each other in the up-down direction in the portion that is leftward relative to the center 52C of the second intake opening 52A and the center 62C of the second exhaust opening 62A. Therefore, the coolant having flown through the second right passage 22 merges with the coolant flowing through the middle passage 30 after flowing to a point that is leftward relative to the center 62C of the second exhaust opening 62A. Thus, the coolant in the second right passage 22 and the coolant in the middle passage 30 can be merged together without significantly hindering the straight flow of the coolant through the inter-port passage 31 and the extension passage 32. Therefore, it is possible to further smooth the coolant flow through the inter-port passage 31. It is also possible to effectively cool the portion around the second exhaust port 62.

[0061] Now, in the cylinder head 4, the dimension between the first exhaust port 61 and the second exhaust port 62 is relatively small. According to the present embodiment, however, along the section shown in FIG. 10, the ratio Ly/Lx of the dimension Ly of the inter-port passage 31 in a direction parallel to the cylinder axial line CA to the dimension Lx thereof in a direction perpendicular to the cylinder axial line CA is greater than 1. That is, along the section, the dimension Ly of the inter-port passage 31 in a direction parallel to the cylinder axial line CA is greater than the dimension Lx thereof in a direction perpendicular to the cylinder axial line CA (i.e., the dimension between the first exhaust port 61 and the second exhaust port 62). Therefore, it is possible to ensure a sufficient passage cross-sectional area of the inter-port passage 31 despite the small dimension of the cylinder head 4 between the first exhaust port 61 and the second exhaust port 62. Therefore, it is possible to effectively cool the portion of the cylinder head 4 between the first exhaust port 61 and the second exhaust port 62.

[0062] On the section shown in FIG. 10 are the first right passage 21, the inter-port passage 31 and the first left passage 41. According to the present embodiment, the inter-port passage 31, among these passages 21, 31 and 41, has the largest ratio of the dimension in a direction parallel to the cylinder axial line CA to the dimension in a direction perpendicular to the cylinder axial line CA. Since the inter-port passage 31 is more vertically elongated as compared with the other passages 21 and 41, it is possible to ensure a large passage cross-sectional area of the inter-port passage 31. Therefore, it is possible to effectively cool the portion of the cylinder head 4 between the first exhaust port 61 and the second exhaust port 62.

[0063] Along the section shown in FIG. 10, the inter-port passage 31 has sides 31a that are parallel to the cylinder axial line CA. Thus, it is possible to effectively cool the portion of the cylinder head 4 between the first exhaust port 61 and the second exhaust port 62.

[0064] According to the present embodiment, as shown in FIG. 9, the water jacket 10A includes the first left passage 41, the second left passage 42 and the third left passage 43. Thus, it is possible to effectively cool the portion leftward of the first exhaust port 61.

[0065] The second left passage 42 extends rightward and upward toward the third left passage 43, and the third left passage 43 extends rightward and downward toward the second left passage 42. Thus, it is possible to effectively cool the portion around the first exhaust port 61.

[0066] Now, if the extension passage 32 is directly connected to the second left passage 42 or the third left passage 43, there is formed a passage that extends in the left-right direction from the second right passage 22 or the third right passage 23 to the second left passage 42 or the third left passage 43. Such a passage will be substantially orthogonal to the inter-port passage 31. In that case, the coolant flow through the inter-port passage 31 is likely to be disturbed by the coolant flowing through this passage. As a result, it may be more difficult for the coolant to flow smoothly through the inter-port passage 31. According to the present embodiment, however, the extension passage 32 is not directly connected to either the second left passage 42 or the third left passage 43. Thus, it is possible to prevent the coolant flow through the inter-port passage 31 from being disturbed. Therefore, it is possible to effectively cool the portion of the cylinder head 4 between the first exhaust port 61 and the second exhaust port 62.

[0067] In the present embodiment, the inlet opening 11 is provided rightward and downward relative to the second exhaust opening 62A. The coolant flowing in through the inlet opening 11 tends to flow leftward and upward. According to the present embodiment, the first left passage 41 includes the diameter-constricted portion 46 that constricts the coolant flow. Therefore, the coolant is prevented from excessively flowing into the first left passage 41. Therefore, a sufficient amount of the coolant flows into the inter-port passage 31. It is possible to effectively cool the portion of the cylinder head 4 between the first exhaust port 61 and the second exhaust port 62.

[0068] Now, as shown in FIG. 6, since the plug hole 55 is inclined relative to the cylinder axial line CA, it is possible to ensure a sufficient space for arranging the camshaft 57 that crosses the cylinder axial line CA and extends in the left-right direction without increasing the size of the cylinder head 4. Therefore, according to the present embodiment, it is possible to reduce the size of the cylinder head 4.

[0069] Although there is no particular limitation on the method for manufacturing the cylinder head 4, it is cast in the present embodiment. The cylinder head 4 is a cast product. Therefore, it is possible to relatively easily form the water jacket 10A configured as described above.

[0070] While one embodiment of the present invention has been described above, the present invention is not limited to the embodiment described above but can be embodied in various other embodiments.

[0071] As viewed along the cylinder axial line CA so that the center 51C of the first intake opening 51A is located leftward and upward of the cylinder axial line CA, the inlet opening 11 does not need to be arranged rightward and downward of the center 62C of the second exhaust opening 62A, and the exit opening 12 does not need to be arranged leftward and upward of the center 51C of the first intake opening 51A.

[0072] The second right passage 22 and the third right passage 23 may be not partitioned from each other in the up-down direction in the portion that is leftward relative to the center 52C of the second intake opening 52A and the center 62C of the second exhaust opening 62A. The second right passage 22 and the third right passage 23 may be connected to the middle passage 30 at a position that is rightward relative to the center 52C of the second intake opening 52A and the center 62C of the second exhaust opening 62A.

[0073] Along a predetermined section (see FIG. 10) that is parallel to a straight line that connects together the center 61C of the first exhaust opening 61A and the center 62C of the second exhaust opening 62A and is parallel to the cylinder axial line CA, the shape of the inter-port passage 31 is not limited to a rectangular shape. There is no particular limitation on the cross-sectional shape of the inter-port passage 31.

[0074] In the embodiment described above, as shown in FIG. 9, the second left passage 42 extends rightward and upward toward the third left passage 43, and the third left passage 43 extends rightward and downward toward the second left passage 42. However, the second left passage 42 does not need to extend rightward toward the third left passage 43. The third left passage 43 does not need to extend rightward toward the second left passage 42.

[0075] In the embodiment described above, the first left passage 41 includes the diameter-constricted portion 46 that constricts the coolant flow. However, the diameter-constricted portion 46 does not need to be provided in the first left passage 41. The diameter-constricted portion 46 may be provided in the second left passage 42, the third left passage 43 or the fourth left passage 44. The diameter-constricted portion 46 may be absent in any part of the left passages 40. The diameter-constricted portion 46 may be provided in a part of one or both of the right passage 20 and the middle passage 30.

[0076] The inlet opening 11 for guiding the coolant from the outside of the engine 1 may be formed on the cylinder body 3. The exit opening 12 for guiding the coolant to the outside of the engine 1 may be formed on the cylinder body 3.

[0077] In the embodiment described above, the cylinder head 4 is provided with one camshaft 57 that crosses the cylinder axial line CA (see FIG. 4). The engine 1 is an SOHC (Single OverHead Camshaft)-type internal combustion engine. However, the present invention is not limited to this. The cylinder head 4 may be provided with an intake camshaft that is arranged upward of the intake valves 53 and 54, and an exhaust camshaft that is arranged upward of the exhaust valves 63 and 64. The engine 1 may be a DOHC (Double OverHead Camshaft)-type internal combustion engine.

REFERENCE SIGNS LIST

[0078] 

1: Internal combustion engine

3: Cylinder body

4: Cylinder head

6: Cylinder

8: Combustion chamber

10A: Water jacket of cylinder head

11: Inlet opening

12: Exit opening

21: First right passage

22: Second right passage

23: Third right passage

30: Middle passage

31: Inter-port passage

32: Extension passage

41: First left passage

42: Second left passage

43: Third left passage

46: Diameter-constricted portion

50: Ignition plug

51: First intake port

51A: First intake opening

52: Second intake port

52A: Second intake opening

55: Plug hole

55A: Ignition opening

55C: Axial line of plug hole

57: Camshaft

57C: Axial line of camshaft

61: First exhaust port

61A: First exhaust opening

62: Second exhaust port

62A: Second exhaust opening

CA: Cylinder axial line

100: Motorcycle (straddled vehicle)

Claims

1. An internal combustion engine (1) comprising:

a cylinder body (3) includes a cylinder (6) formed therein that extends along a cylinder axial line (CA) and defines a portion of a combustion chamber (8);

a cylinder head (4) secured on the cylinder body (3);

a first intake port (51) formed on the cylinder head (4) and including a first intake opening (51A) facing toward the combustion chamber (8), wherein an intake air to be taken into the combustion chamber (8) flows through the first intake port (51);

a second intake port (52) formed on the cylinder head (4) and including a second intake opening (52A) facing toward the combustion chamber (8), wherein an intake air to be taken into the combustion chamber (8) flows through the second intake port (52);

a first exhaust port (61) formed on the cylinder head (4) and including a first exhaust opening (61A) facing toward the combustion chamber (8), wherein an exhaust air to be exhausted from the combustion chamber (8) flows through the first exhaust port (61);

a second exhaust port (62) formed on the cylinder head (4) and including a second exhaust opening (62A) facing toward the combustion chamber (8), wherein an exhaust air to be exhausted from the combustion chamber (8) flows through the second exhaust port (62);

a plug hole (55) formed on the cylinder head (4) and including an ignition opening (55A) facing toward the combustion chamber (8), wherein an ignition plug (50) is accommodated in the plug hole (55); and

a water jacket (10A) formed on the cylinder head (4), wherein a coolant flows through the water jacket (10A),

wherein as viewed along the cylinder axial line (CA) so that a center (51C) of the first intake opening (51A) is located leftward and upward of the cylinder axial line (CA):

a center (52C) of the second intake opening (52A) is located rightward and upward of the cylinder axial line (CA), a center (61C) of the first exhaust opening (61A) is located leftward and downward of the cylinder axial line (CA), and a center (62C) of the second exhaust opening (62A) is located rightward and downward of the cylinder axial line (CA);

an axial line (55C) of the plug hole (55) is inclined relative to the cylinder axial line (CA) so as to diverge leftward of the cylinder axial line (CA) while extending away from the ignition opening (55A) along the cylinder axial line (CA);

the plug hole (55) is located between the first intake port (51) and the first exhaust port (61);

the water jacket (10A) includes a middle passage (30), wherein the middle passage (30) includes an inter-port passage (31) that is located between the first exhaust port (61) and the second exhaust port (62) and downward of the cylinder axial line (CA), and an extension passage (32) that extends upward from the inter-port passage (31) to a position that is upward of the cylinder axial line (CA).

2. The internal combustion engine (1) according to claim 1, wherein as viewed along the cylinder axial line (CA) so that the center (51C) of the first intake opening (51A) is located leftward and upward of the cylinder axial line (CA):

the water jacket (10A) includes a first right passage (21) that is located rightward and downward relative to a center (62D) of the second exhaust port (62), a second right passage (22) that is located upward relative to the center (62D) of the second exhaust port (62) and is connected to the first right passage (21) and the middle passage (30), and a third right passage (23) that is located upward relative to the second right passage (22) and downward relative to a center (52D) of the second intake port (52) and is connected to the middle passage (30); and

the second right passage (22) and the third right passage (23) are partitioned from each other in an up-down direction in a portion that is leftward relative to the center (52C) of the second intake opening (52A) and the center (62C) of the second exhaust opening (62A).

3. The internal combustion engine (1) according to claim 1 or 2, wherein along a predetermined section (X-X) that is parallel to a straight line that connects together the center (61C) of the first exhaust opening (61A) and the center (62C) of the second exhaust opening (62A) and is parallel to the cylinder axial line (CA), a ratio of a dimension (Ly) of the inter-port passage (31) in a direction (Y) that is parallel to the cylinder axial line (CA) to a dimension (Lx) thereof in a direction (X) that is perpendicular to the cylinder axial line (CA) is greater than 1.

4. The internal combustion engine (1) according to claim 3, wherein along the predetermined section (X-X), the inter-port passage (31) has a side (31a) that is parallel to the cylinder axial line (CA).

5. The internal combustion engine (1) according to any one of claims 1 to 4, wherein as viewed along the cylinder axial line (CA) so that the center (51C) of the first intake opening (51A) is located leftward and upward of the cylinder axial line (CA):
the water jacket (10A) includes a first left passage (41) that is located downward relative to a center (61D) of the first exhaust port (61), a second left passage (42) that is located leftward and upward relative to the center (61D) of the first exhaust port (61) and is connected to the first left passage (41), and a third left passage (43) that is located leftward and downward relative to a center (51D) of the first intake port (51) and is connected to the second left passage (42).

6. The internal combustion engine (1) according to claim 5, wherein the extension passage (32) and the second left passage (42) are not directly connected to each other, and the extension passage (32) and the third left passage (43) are not directly connected to each other.

7. The internal combustion engine (1) according to claim 5 or 6, wherein as viewed along the cylinder axial line (CA) so that the center (51C) of the first intake opening (51A) is located leftward and upward of the cylinder axial line (CA):

the second left passage (42) extends rightward and upward toward the third left passage (43); and

the third left passage (43) extends rightward and downward toward the second left passage (42).

8. The internal combustion engine (1) according to any one of claims 5 to 7, wherein along a predetermined section (X-X) that is parallel to a straight line that connects together the center (61C) of the first exhaust opening (61A) and the center (62C) of the second exhaust opening (62A) and is parallel to the cylinder axial line (CA), a ratio of a dimension (Ly;LRy;LLy) in a direction (Y) that is parallel to the cylinder axial line (CA) to a dimension (Lx;LRx;LLy) in a direction (X) that is perpendicular to the cylinder axial line (CA) is greater for the inter-port passage (31) than for the first right passage (21) and for the first left passage (41).

9. The internal combustion engine (1) according to any one of claims 5 to 8, wherein as viewed along the cylinder axial line (CA) so that the center (51C) of the first intake opening (51A) is located leftward and upward of the cylinder axial line (CA):

the water jacket (10A) includes an inlet opening (11) that is located rightward and downward relative to the second exhaust opening (62A), wherein the coolant flows in through the inlet opening (11); and

the first left passage (41) includes a diameter-constricted portion (46) that constricts the coolant flow.

10. The internal combustion engine according to any one of claims 1 to 8, wherein as viewed along the cylinder axial line (CA) so that the center (51C) of the first intake opening (51A) is located leftward and upward of the cylinder axial line (CA):
the water jacket (10A) includes an inlet opening (11) that is located rightward and downward relative to the second exhaust opening (62A), wherein the coolant flows in through the inlet opening (11).

11. The internal combustion engine (1) according to any one of claims 1 to 8, wherein:

the internal combustion engine (1) includes an inlet opening (11) for guiding the coolant from an outside of the internal combustion engine (1) to an inside of the internal combustion engine (1); and

the inlet opening (11) is formed on the cylinder head (4).

12. The internal combustion engine (1) according to any one of claims 1 to 8, wherein:

the internal combustion engine (1) includes an inlet opening (11) for guiding the coolant from an outside of the internal combustion engine (1) to an inside of the internal combustion engine (1) and an exit opening (12) for guiding the coolant to the outside of the internal combustion engine (1); and

the inlet opening (11) and the exit opening (12) are formed on the cylinder head (4).

13. The internal combustion engine (1) according to any one of claims 1 to 12, wherein:

the internal combustion engine (1) includes a camshaft (57) that is rotatably supported on the cylinder head (4) and crosses the cylinder axial line (CA); and

an axial line (57C) of the camshaft (57) is located between the center (51C) of the first intake opening (51A) and the center (61C) of the first exhaust opening (61A) and is located between the center (52C) of the second intake opening (52A) and the center (62C) of the second exhaust opening (62A).

14. The internal combustion engine (1) according to any one of claims 1 to 13, wherein the cylinder head (4) is a cast product.

15. A straddled vehicle (100) comprising the internal combustion engine (1) according to any one of claims 1 to 14.

Drawing