EP3842629B1 - Internal combustion engine, straddled vehicle, and method for manufacturing internal combustion engine - Google Patents
Internal combustion engine, straddled vehicle, and method for manufacturing internal combustion engine Download PDFInfo
- Publication number
- EP3842629B1 EP3842629B1 EP20202139.0A EP20202139A EP3842629B1 EP 3842629 B1 EP3842629 B1 EP 3842629B1 EP 20202139 A EP20202139 A EP 20202139A EP 3842629 B1 EP3842629 B1 EP 3842629B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- cylinder
- hole
- water jacket
- cylinder body
- depressed
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Links
- 238000002485 combustion reaction Methods 0.000 title claims description 61
- 238000000034 method Methods 0.000 title claims description 21
- 238000004519 manufacturing process Methods 0.000 title claims description 13
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 110
- 230000000994 depressogenic effect Effects 0.000 claims description 92
- 238000001816 cooling Methods 0.000 claims description 57
- 238000000465 moulding Methods 0.000 claims description 30
- 239000002826 coolant Substances 0.000 claims description 17
- 239000007769 metal material Substances 0.000 claims description 10
- 239000000203 mixture Substances 0.000 description 9
- 230000007423 decrease Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 239000004411 aluminium Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 239000002828 fuel tank Substances 0.000 description 1
Images
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
- F02F1/00—Cylinders; Cylinder heads
- F02F1/02—Cylinders; Cylinder heads having cooling means
- F02F1/10—Cylinders; Cylinder heads having cooling means for liquid cooling
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/06—Permanent moulds for shaped castings
- B22C9/065—Cooling or heating equipment for moulds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/22—Moulds for peculiarly-shaped castings
- B22C9/24—Moulds for peculiarly-shaped castings for hollow articles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D15/00—Casting using a mould or core of which a part significant to the process is of high thermal conductivity, e.g. chill casting; Moulds or accessories specially adapted therefor
- B22D15/02—Casting using a mould or core of which a part significant to the process is of high thermal conductivity, e.g. chill casting; Moulds or accessories specially adapted therefor of cylinders, pistons, bearing shells or like thin-walled objects
Definitions
- the present invention relates to a method for manufacturing an internal combustion engine having a water jacket through which coolant passes, particularly for a straddled vehicle.
- a water-cooled internal combustion engine includes a water jacket through which a coolant flows and which is formed in a portion of the cylinder body around the cylinder (see, for example, JP2011-167706A (Honda Motor Co Ltd )).
- FIG. 13 is a partial cross-sectional view schematically showing an example of a conventional water-cooled internal combustion engine.
- Designations 201, 202 and 203 denote the cylinder body, the cylinder head and the bolts, respectively.
- the cylinder body 201 includes a cylinder 204, and a water jacket 205 is formed in a portion of the cylinder body 201 around the cylinder 204.
- a piston 206 is arranged inside the cylinder 204.
- the cylinder head 202, the cylinder 204 and the piston 206 together define a combustion chamber 207.
- a gasket is interposed between the cylinder head 202 and the cylinder body 201. Since the cylinder head 202 and the cylinder body 201 are fastened together by the bolts 203, the cylinder body 201 is in close contact with the cylinder head 202 with the gasket therebetween. The portion of the cylinder body 201 around the cylinder 204 is under a pressure (hereinafter referred to as the surface pressure) from the cylinder head 202.
- An internal combustion engine repeatedly goes through a cycle of intake, compression, combustion and exhaust. During the combustion stroke, the mixture combusts in the combustion chamber 207. This combustion creates a force on the cylinder head 202 in the direction away from the cylinder body 201 (upward in FIG. 13 ). In other words, the cylinder head 202 is under a force such as to lift the cylinder head 202 off the cylinder body 201. During the process, the surface pressure applied to the portion around the cylinder 204 fluctuates. In order to suppress the fluctuation of the surface pressure, there is a need to increase the fastening force of the bolts 203.
- the bolts 203 need to be designed to have a structure such that it is possible to endure the increased fastening force by, for example, increasing the thickness of the bolts 203, and it is necessary to ensure a sufficient thickness of the cylinder body 201 and the cylinder head 202. As a result, it may lead to an increase in cost and size of the internal combustion engine.
- An object of at least one embodiment of at least one aspect of the present invention may be to obviate or at least mitigate one or more problems and/or disadvantages in the prior art.
- An object of at least one embodiment of at least one aspect of the present invention may be to seek to provide an internal combustion engine including a water jacket formed in a portion of the cylinder body around the cylinder, wherein it may be possible to suppress an increase in cost and size of the internal combustion engine by suppressing the fluctuation of the surface pressure applied to the portion around the cylinder.
- a method for manufacturing an internal combustion engine wherein the internal combustion engine comprises:
- the first depressed portion of the cylinder body may be formed next to the cooling passage of the water jacket molding portion.
- a method for manufacturing an internal combustion engine wherein the internal combustion engine comprises:
- an internal combustion engine manufactured by the method of the first or second aspect of the present invention.
- the surface of the cylinder body that opposes the cylinder head may comprise the first opposing surface on the outer side relative to the water jacket and the second opposing surface on the inner side relative to the water jacket. Since the first bolt fastens the cylinder head to the cylinder body, the first opposing surface and the second opposing surface may be under a pressure from the cylinder head.
- the provision of the first depressed portion may decrease the volume of a portion of the first opposing surface in the vicinity of the first hole and accordingly may decrease the rigidity thereof, as compared with a case where the first depressed portion is absent.
- the rigidity of the second opposing surface may be (relatively) higher than the rigidity of the first opposing surface.
- the surface pressure between the first opposing surface and the cylinder head may be lower while the surface pressure between the second opposing surface and the cylinder head may be higher. Therefore, it may be possible to suppress the fluctuation of the surface pressure applied to the portion of the cylinder body around the cylinder during the combustion of the mixture. Thus, it may be possible to suppress an increase in cost and size of the internal combustion engine.
- the cylinder body may comprise a second hole that may be formed outward of the water jacket in the radial direction of the cylinder and that may extend parallel to the axial line of the cylinder.
- the internal combustion engine may comprise a second bolt that may be inserted into the second hole to fasten together the cylinder head and the cylinder body.
- the outer contour may comprise a second depressed portion that may be located radially outward of the second hole and/or that may be depressed in a direction radially outward of the cylinder.
- the inner contour may comprise an arc that may be centered at a center of the cylinder and that may have a first curvature.
- a portion of the outer contour between the first depressed portion and the second depressed portion may comprise an arc whose center may be off the center of the cylinder, and that may have a second curvature smaller than the first curvature.
- the width of the water jacket may be larger and/or the area of the first opposing surface may be smaller, as compared with a case where a portion of the water jacket between the first depressed portion and/or the second depressed portion of the outer contour may be an arc that may be centered at the center of the cylinder. Therefore, the rigidity of the second opposing surface may be relatively high/higher than the rigidity of the first opposing surface.
- the surface pressure between the first opposing surface and the cylinder head may be lower while the surface pressure between the second opposing surface and the cylinder head may be higher. This further suppresses the fluctuation of the surface pressure applied to the portion of the cylinder body around the cylinder during the combustion of the mixture. Thus, it may be possible to further suppress an increase in cost and size of the internal combustion engine.
- an entirety of a portion of the outer contour between the first depressed portion and the second depressed portion may be an arc whose center may be off the center of the cylinder, and that may have a second curvature smaller than the first curvature.
- the area of the second opposing surface may increase and the rigidity of the second opposing surface may become relatively higher. Therefore, the surface pressure between the second opposing surface and the cylinder head may further increase. This may further suppress the fluctuation of the surface pressure applied to the portion of the cylinder body around the cylinder during the combustion of the mixture. Thus, it may be possible to further suppress an increase in cost and size of the internal combustion engine.
- an angle between a first straight line, which may connect between the center of the cylinder and the center of the first hole, and a second straight line that may connect between the center of the cylinder and a point along the first depressed portion that may be farthest away from the center of the cylinder may be 5° to 15°.
- the first depressed portion may be provided in the vicinity of the first hole into which the first bolt may be inserted.
- the advantageous effects described above may be pronounced as compared with a case where the first depressed portion may be provided far away from the first hole.
- a length, between the cylinder and the water jacket, of a first straight line that connects between the center of the cylinder and the center of the first hole may be longer than a length, between the first hole and the water jacket, of the first straight line.
- the area of the second opposing surface may be large in the vicinity of the first hole.
- the rigidity of the second opposing surface may be high, thereby increasing the surface pressure between the second opposing surface and the cylinder head. This may further suppress the fluctuation of the surface pressure applied to the portion of the cylinder body around the cylinder during the combustion of the mixture. Thus, it may be possible to further suppress an increase in cost and size of the internal combustion engine.
- a contour of a bottom portion of the water jacket may comprise an outer curve portion that may be located on a side of the first hole and an inner curve portion that may be located on a side of the cylinder.
- a curvature of the outer curve portion may be smaller than a curvature of the inner curve portion.
- the first bolt may be inserted into the first hole, a portion of the cylinder body close to the first hole may be bound by the first bolt.
- a large local stress may occur on the portion close to the first hole.
- the curve (outer curve portion) of a portion of the bottom portion of the water jacket that may be close to the first hole may be more gentle than the curve (inner curve portion) of a portion thereof that may be close to the cylinder. Therefore, it may be possible to reduce the stress on the portion of the bottom portion of the water jacket that may be close to the first hole. Thus, it may be possible to improve the durability of the cylinder body.
- the cylinder body may comprise another cylinder that may extend parallel to the cylinder, and a third hole that may extend parallel to the axial line of the cylinder.
- the internal combustion engine may comprise a third bolt that may be inserted into the third hole to fasten together the cylinder head and the cylinder body.
- a straight line may pass through between the first hole and the second hole, wherein the straight line may pass through the center of the cylinder and/or may be perpendicular to a straight line that may pass through the center of the cylinder and/or a center of the other cylinder.
- a straight line may pass through between the second hole and the third hole, wherein the straight line may pass through the center of the other cylinder and/or may be perpendicular to the straight line that connects between the center of the cylinder and the center of the other cylinder.
- the water jacket may be formed around the cylinder and/or the other cylinder.
- the outer contour may comprise a third depressed portion that may be located radially outward of the third hole and/or may be depressed in a direction radially outward of the other cylinder.
- the advantageous effect(s) described above can be realized for a multi-cylinder internal combustion engine.
- a straddled vehicle comprising an internal combustion engine according to the aforementioned implementation of the present invention.
- the straddled vehicle may comprise a driving wheel that may be linked to the internal combustion engine with a power transmitting member therebetween and/or that may be driven by the internal combustion engine.
- a coolant may be supplied to flow through the cooling passage during the molding process, thereby desirably cooling the mold. Therefore, it may be possible to reliably prevent the mold from being burnt, and/or it may be possible to realize a high-quality cylinder body.
- the first depressed portion of the cylinder body may be formed next to the cooling passage of the water jacket molding portion.
- the cooling passage can be formed in the water jacket molding portion without imposing design restrictions.
- the manufacturing method according to the second aspect of the present invention described above it may be possible to increase the width of the water jacket molding portion for the presence of the first depressed portion. Thus, it may be possible to ensure a space for the first cooling passage.
- the first cooling passage can be formed in the water jacket molding portion without imposing design restrictions.
- the connecting portion between cylinders is not easily cooled and is likely to be hot during the molding process.
- the second cooling passage is formed next to the connecting portion between cylinders in the water jacket molding portion, it is possible to effectively cool the connecting portion. Therefore, it may be possible to reliably prevent the mold from being burnt, and/or it may be possible to realize a high-quality cylinder body.
- an internal combustion engine comprising a water jacket formed in a portion of the cylinder body around the cylinder, wherein it may be possible to suppress an increase in cost and size of the internal combustion engine by suppressing the fluctuation of the surface pressure applied to the portion around the cylinder.
- FIG. 1 is a side view of a motorcycle 1, which is an example of a straddled vehicle.
- the motorcycle 1 includes a front wheel 2, a rear wheel 3, an internal combustion engine (hereinafter referred to as "the engine") 10, a handle 4, a fuel tank 5, and a seat 6.
- the engine 10 is linked to the rear wheel 3 by a power transmitting member such as a chain 7.
- the rear wheel 3 is a driving wheel that is driven by the engine 10.
- the engine 10 ha a crankcase 11, a cylinder body 12 connected to the crankcase 11, a cylinder head 13 connected to the cylinder body 12, and a cylinder head cover 14 connected to the cylinder head 13.
- the engine 10 is a multi-cylinder engine.
- the engine 10 is a three-cylinder engine having a first cylinder 31, a second cylinder 32 and a third cylinder 33.
- the cylinder head 13 is provided with an ignitor 16, an intake valve (not shown) and an exhaust valve 18.
- the first to third cylinders 31 to 33 are provided inside the cylinder body 12.
- a piston 19 is accommodated inside each of the cylinders 31 to 33.
- the cylinder head 13, the cylinders 31 to 33 and the pistons 19 together define a combustion chamber 58.
- the piston 19 is linked to a crankshaft 21 by a connecting rod 20.
- the crankshaft 21 is arranged inside the crankcase 11.
- the crankshaft 21 extends in a vehicle width direction.
- a generator 22 is attached to a left end portion of the crankshaft 21.
- a sprocket 23 is attached to a right end portion of the crankshaft 21.
- a cam chain 24 is wound around the sprocket 23.
- the cam chain 24 is also wound around a sprocket 26 attached to a camshaft 25.
- the engine 10 is a water-cooled engine. As shown in FIG. 3 , the cylinder body 12 has water jackets 121 and 12W through which coolant passes. The cylinder head 13 also has a water jacket 13W through which the coolant passes. A gasket 28 is interposed between the cylinder body 12 and the cylinder head 13. As will be described later, the gasket 28 has a plurality of holes 28a and 28b (see FIG. 8 ). The water jacket 12W of the cylinder body 12 and the water jacket 13W of the cylinder head 13 communicate with each other through the holes 28a and 28b of the gasket 28.
- FIG. 4 and FIG. 5 are plan views of the cylinder body 12. Specifically, these figures show the cylinder body 12 as seen along the axial line (hereinafter referred to as the "cylinder axial line") 31c of the first cylinder 31.
- cylinder axial line hereinafter referred to as the "cylinder axial line" 31c of the first cylinder 31.
- “as shown in FIG. 4” and “as shown in FIG. 5” mean that the cylinder body 12 is seen along the first cylinder axial line 31c.
- the first to third cylinders 31 to 33 are arranged parallel to each other, the axial line of the second cylinder 32 and the axial line of the third cylinder 33 are parallel to the cylinder axial line 31c of the first cylinder 31.
- the water jacket 12W is formed around the first cylinder 31, the second cylinder 32 and the third cylinder 33.
- the water jacket 12W has a first water jacket portion 31W around the first cylinder 31, a second water jacket portion 32W around the second cylinder 32, and a third water jacket portion 33W around the third cylinder 33.
- the first water jacket portion 31W is connected to the second water jacket portion 32W
- the second water jacket portion 32W is connected to the third water jacket portion 33W.
- the water jacket 12W is defined by an outer contour 35 and an inner contour 36.
- the outer contour 35 has a first outer contour 351 that defines the outer side of the first water jacket portion 31W in the radial direction of the first cylinder 31, a second outer contour 352 that defines the outer side of the second water jacket portion 32W in the radial direction of the second cylinder 32, and a third outer contour 353 that defines the outer side of the third water jacket portion 33W in the radial direction of the third cylinder 33.
- the inner contour 36 has a first inner contour 361 that defines the inner side of the first water jacket portion 31W in the radial direction of the first cylinder 31, a second inner contour 362 that defines the inner side of the second water jacket portion 32W in the radial direction of the second cylinder 32, and a third inner contour 363 that defines the inner side of the third water jacket portion 33W in the radial direction of the third cylinder 33.
- designation 3512 denotes a boundary between the first outer contour 351 and the second outer contour 352.
- Designation 3523 denotes a boundary between the second outer contour 352 and the third outer contour 353.
- Designation 3612 denotes a boundary between the first inner contour 361 and the second inner contour 362.
- Designation 3623 denotes a boundary between the second inner contour 362 and the third inner contour 363.
- the cylinder body 12 has first to fourth holes 41 to 44 into which bolts 29 (see FIG. 6 ) for fastening together the cylinder head 13 and the cylinder body 12 are inserted.
- the first to fourth holes 41 to 44 extend parallel to the cylinder axial line 31c.
- the cylinder head 13 has a second hole 42A that corresponds to the second hole 42 of the cylinder body 12, and a third hole 43A that corresponds to the third hole 43 of the cylinder body 12.
- a bolt 29 is inserted into the second hole 42 of the cylinder body 12 and the second hole 42A of the cylinder head 13.
- a bolt 29 is inserted into the third hole 43 of the cylinder body 12 and the third hole 43A of the cylinder head 13.
- the cylinder head 13 has a first hole that corresponds to the first hole 41 of the cylinder body 12, and a fourth hole that corresponds to the fourth hole 44 of the cylinder body 12.
- a bolt 29 is inserted into the first hole 41 of the cylinder body 12 and the first hole of the cylinder head 13.
- a bolt 29 is inserted into the fourth hole 44 of the cylinder body 12 and the fourth hole of the cylinder head 13.
- the cylinder head 13 and the cylinder body 12 are fastened together by these bolts 29. Note that the piston 19 is not shown in FIG. 6 .
- a straight line that passes through centers 31c to 33c of the first to third cylinders 31 to 33 is denoted as L3.
- a straight line that passes through the center 31c of the first cylinder 31 and is perpendicular to the straight line L3 is denoted as L11.
- a straight line that passes through the center 32c of the second cylinder 32 and is perpendicular to the straight line L3 is denoted as L12. Then, the straight line L11 passes through between the first hole 41 and the second hole 42.
- the straight line L12 passes through between the second hole 42 and the third hole 43.
- the cylinder body 12 has a first opposing surface 51 that is located outward of the outer contour 35 in the radial direction of the first cylinder 31, and a second opposing surface 52 that is located inward of the inner contour 36 in the radial direction of the first cylinder 31.
- the first opposing surface 51 has an opposing surface 511 that is located outward of the first outer contour 351 in the radial direction of the first cylinder 31, an opposing surface 512 that is located outward of the second outer contour 352 in the radial direction of the second cylinder 32, and an opposing surface 513 that is located outward of the third outer contour 353 in the radial direction of the third cylinder 33.
- the second opposing surface 52 has an opposing surface 521 that is located inward of the first inner contour 361 in the radial direction of the first cylinder 31, an opposing surface 522 that is located inward of the second inner contour 362 in the radial direction of the second cylinder 32, and an opposing surface 523 that is located inward of the third inner contour 363 in the radial direction of the third cylinder 33.
- the first opposing surface 51 and the second opposing surface 52 oppose the cylinder head 13.
- the gasket 28 is interposed between the cylinder head 13 and the cylinder body 12.
- the first opposing surface 51 and the second opposing surface 52 oppose the cylinder head 13 with the gasket 28 therebetween.
- "opposing the cylinder head” means both directly opposing the cylinder head and indirectly opposing the cylinder head with a gasket, or the like, therebetween.
- the outer contour 35 has depressed portions 70, 71 and 72 that are located around the first cylinder 31.
- the depressed portion 71 is located radially outward of the first hole 41 and is depressed in the direction radially outward of the first cylinder 31.
- the depressed portion 72 is located radially outward of the second hole 42 and is depressed in the direction radially outward of the first cylinder 31.
- the outer contour 35 has depressed portions 73 and 74 that are located around the second cylinder 32, and depressed portions 75, 76 and 77 that are located around the third cylinder 33.
- the depressed portion 73 is located radially outward of the second hole 42 and is depressed in the direction radially outward of the second cylinder 32.
- the depressed portion 74 is located radially outward of the third hole 43 and is depressed in the direction radially outward of the second cylinder 32.
- the depressed portion 75 is located radially outward of the third hole 43 and is depressed in the direction radially outward of the third cylinder 33.
- the depressed portions 76 and 77 are located radially outward of the fourth hole 44 and are depressed in the direction radially outward of the third cylinder 33.
- the depressed portions 71, 72 and 74 may be referred to as the first depressed portion, the second depressed portion and the third depressed portion, respectively.
- a straight line that connects between the center 31c of the cylinder 31 and a center 41c of the first hole 41 is denoted as a first straight line L1.
- a straight line that connects between the center 31c of the cylinder 31 and a point along the first depressed portion 71 that is farthest away from the center 31c of the cylinder 31 is denoted as a second straight line L2.
- the angle ⁇ between the first straight line L1 and the second straight line L2 is 5° to 15°.
- the first depressed portion 71 is provided in the vicinity of the first hole 41. Note, however, that the value of the angle ⁇ above is merely an example, and there is no particular limitation thereto.
- the first inner contour 361 is an arc 37a that is centered at the center 31c of the cylinder 31 and that has a first curvature. While the arc 37a may be only a portion of the first inner contour 361, the arc 37a is herein the entirety of the first inner contour 361.
- a portion of the first outer contour 351 between the first depressed portion 71 and the second depressed portion 72 is an arc 38a whose center 39c is off the center 31c of the cylinder 31, and that has a second curvature smaller than the first curvature.
- the arc 38a of the first outer contour 351 is located upward of the arc 37a of the first inner contour 361, and the center 39c of the arc 38a is located downward of the center 31c of the arc 37a.
- the arc 38a may be only a portion of the first outer contour 351 that is between the first depressed portion 71 and the second depressed portion 72, the arc 38a is herein the entirety of the first outer contour 351 between the first depressed portion 71 and the second depressed portion 72.
- the positional relationship between the second inner contour 362 and the second outer contour 352 and the positional relationship between the third inner contour 363 and the third outer contour 353 are similar to the positional relationship between the first inner contour 361 and the first outer contour 351.
- a portion or whole of the second inner contour 362 is an arc 37b that is centered at the center 32c of the second cylinder 32 and that has the first curvature.
- a portion or whole of the third inner contour 363 is an arc 37c that is centered at the center 33c of the third cylinder 33 and that has the first curvature.
- a portion or whole of the second outer contour 352 between the depressed portion 73 and the depressed portion 74 is an arc 38b whose center is off the center 32c of the second cylinder 32 and that has the second curvature.
- a portion or whole of the third outer contour 353 between the depressed portion 75 and the depressed portion 76 is an arc 38c whose center is off the center 33c of the third cylinder 33 and that has the second curvature.
- the length N1 of the first straight line L1 between the first cylinder 31 and the water jacket 12W is longer than the length N2 thereof between the first hole 41 and the water jacket 12W.
- the area of the second opposing surface 52 is relatively large.
- FIG. 7 is a partial cross-sectional view of the cylinder body 12 taken along the first straight line L1.
- a contour 55 of the bottom portion of the water jacket 12W has an outer curve portion 55a that is located on the side of the first hole 41 and an inner curve portion 55b that is located on the side of the first cylinder 31.
- the outer curve portion 55a is more gently curved than the inner curve portion 55b.
- the curvature of the outer curve portion 55a is smaller than the curvature of the inner curve portion 55b.
- the curvature of the outer curve portion 55a and the curvature of the inner curve portion 55b may each be constant or not constant. Where the curvature of the outer curve portion 55a and the curvature of the inner curve portion 55b are not constant, they refer to the mean curvature of the outer curve portion 55a and the mean curvature of the inner curve portion 55b.
- FIG. 8 is a plan view of the gasket 28.
- the gasket 28 has holes 31h to 33h that correspond to the first to third cylinders 31 to 33, and first to fourth holes 41h to 44h into which the bolts 29 are inserted.
- the gasket 28 also has the holes 28a and 28b through which the coolant passes.
- the hole 28a is arranged over the water jacket 121 of the cylinder body 12.
- the holes 28b are arranged over the water jacket 12W of the cylinder body 12.
- the coolant in the water jacket 121 flows into the water jacket 13W of the cylinder head 13 (see an arrow in FIG. 3 ) through the hole 28a.
- the coolant in the water jacket 13W flows into the water jacket 12W of the cylinder body 12 (see arrows in FIG. 3 ) through the holes 28b.
- the cylinder body 12 and the cylinder head 13 are cooled by the coolant flowing through the water jacket 121, the water jacket 13W and the water jacket 12W in this order.
- the engine 10 is configured as described above. As described above, the cylinder head 13 is fastened to the cylinder body 12 by the bolts 29 (see FIG. 6 ). The first opposing surface 51 and the second opposing surface 52 of the cylinder body 12 are pressed against the cylinder head 13. The first opposing surface 51 and the second opposing surface 52 are under a pressure from the cylinder head 13 (hereinafter referred to as the surface pressure).
- the engine 10 repeatedly goes through a cycle of intake, compression, combustion and exhaust. During the combustion stroke, the mixture of fuel and air combusts in the combustion chamber 58. This combustion creates a force such as to lift the cylinder head 13 off the cylinder body 12.
- the surface pressure applied to the first opposing surface 51 and the second opposing surface 52 fluctuates.
- One possible way to suppress the fluctuation of the surface pressure is to increase the fastening force of the bolts 29.
- the cylinder body 12 and the cylinder head 13 need to be designed so that they can endure such an increased fastening force. Without some countermeasures, this will lead to an increase in cost and size of the engine 10.
- the outer contour 35 of the water jacket 12W has the depressed portions 70 to 77 as the cylinder body 12 is seen along the cylinder axial line 31c as shown in FIG. 4 .
- the outer contour 35 of the water jacket 12W is partially depressed in the vicinity of the first to fourth holes 41 to 44 into which the bolts 29 are inserted. Therefore, as compared with a case where the depressed portions 70 to 77 are absent, the area of the first opposing surface 51 is smaller in the vicinity of the first to fourth holes 41 to 44.
- the ratio of the area of the second opposing surface 52 with respect to the total area of the first opposing surface 51 and the second opposing surface 52 is larger as compared with a case where the depressed portions 70 to 77 are absent. Therefore, with the engine 10 according to the present embodiment, the rigidity of the second opposing surface 52 is relatively larger than the rigidity of the first opposing surface 51.
- the surface pressure between the first opposing surface 51 and the cylinder head 13 decreases, but the surface pressure between the second opposing surface 52 and the cylinder head 13 increases. Therefore, it is possible to suppress the fluctuation of the surface pressure applied to portions of the cylinder body 12 around the first to third cylinders 31 to 33 during the combustion of the mixture.
- a portion of the outer contour 35 of the water jacket 12W between the first depressed portion 71 and the second depressed portion 72 is the arc 38a whose center 39c is off the center 31c of the cylinder 31 as the cylinder body 12 is seen along the cylinder axial line 31c as shown in FIG. 4 .
- the curvature of the arc 38a (the second curvature) is smaller than the curvature of the arc 37a of the inner contour 36 (the first curvature).
- the width of the water jacket 12W increases and the area of the first opposing surface 51 decreases, as compared with a case where a portion of the outer contour 35 that is between the first depressed portion 71 and the second depressed portion 72 is an arc that is centered at the center 31c of the cylinder 31 and that has the first curvature.
- This further relatively increases the rigidity of the second opposing surface 52 and further increases the surface pressure between the second opposing surface 52 and the cylinder head 13. Therefore, it is possible to further suppress an increase in cost and size of the engine 10.
- the position of the first depressed portion 71 of the outer contour 35 is such that the angle ⁇ is 5° to 15°, wherein ⁇ is the angle between the first straight line L1 that connects between the center 31c of the first cylinder 31 and the center 41c of the first hole 41 and the second straight line L2 that connects between the center 31c of the first cylinder 31 and a point along the first depressed portion 71 that is farthest away from the center 31c of the first cylinder 31 as the cylinder body 12 is seen along the cylinder axial line 31c as shown in FIG. 5 in the present embodiment.
- the provision of the first depressed portion 71 near the first hole 41 enhances the advantageous effects described above. Note that this similarly applies also to the other depressed portions 70 and 72 to 77.
- the length N1 of the first straight line L1 between the first cylinder 31 and the water jacket 12W is longer than the length N2 thereof between the first hole 41 and the water jacket 12W as the cylinder body 12 is seen along the cylinder axial line 31c as shown in FIG. 5 .
- the area of the second opposing surface 52 is larger. This increase the rigidity of the second opposing surface 52 and the surface pressure between the second opposing surface 52 and the cylinder head 13 in the vicinity of the first hole 41. Therefore, it is possible to further suppress an increase in cost and size of the engine 10. Note that although the description is omitted, this similarly applies also to portions in the vicinity of the other holes 42 to 44.
- the contour 55 of the bottom portion of the water jacket 12W includes the outer curve portion 55a that is located on the side of the first hole 41 and the inner curve portion 55b that is located on the side of the first cylinder 31. Since the bolt 29 is inserted in the first hole 41, a portion of the cylinder body 12 that is close to the first hole 41 is bound by the bolt 29. During the combustion of the mixture, there may occur a large local stress on a portion that is close to the first hole 41.
- the curvature of the outer curve portion 55a is smaller than the curvature of the inner curve portion 55b.
- the curve of a portion of the bottom portion of the water jacket 12W that is close to the first hole 41 is more gentle than the curve of a portion thereof that is close to the cylinder 31. Therefore, it is possible to reduce the stress on the portion of the bottom portion of the water jacket 12W that is close to the first hole 41. Thus, it is possible to improve the durability of the cylinder body 12.
- the engine 10 is manufactured by manufacturing the cylinder body 12 and the cylinder head 13, and fastening the cylinder body 12 and the cylinder head 13 together by the bolts 29.
- the cylinder body can be manufactured as follows, for example.
- a mold 112 is prepared. As shown in FIG. 9 , the mold 112 has cylinder molding portions 131 to 133 having the same shape as the first to third cylinders 31 to 33, water jacket molding portions 1121 and 112W having the same shape as the water jackets 121 and 12W, and bolt hole molding portions 141 to 144 having the same shape as the first to fourth holes 41 to 44. Although not shown in FIG. 9 , cooling passages, through which a coolant such as water flows, are formed inside the water jacket molding portion 112W and the bolt hole molding portions 141 to 144. FIG.
- cooling passages 101 and 102 are a perspective view drawn so that cooling passages 101 and 102 formed inside the water jacket molding portion 112W and cooling passages 103 formed inside the bolt hole molding portions 141 to 144 are visible.
- the cooling passages 101 and 102 may be referred to as the first cooling passage and the second cooling passage, respectively.
- the mold 112 When manufacturing the cylinder body 12, the mold 112 is prepared, and then a metal material is injected into the mold 112.
- the metal material may be any of various metal materials known in the art, e.g. aluminium.
- a coolant is supplied to flow through the cooling passages 101 to 103, thereby cooling the mold 112 and the metal material.
- it may be before, during or after the process of injecting a metal material into the mold 112.
- FIG. 11 is a plan view of the cylinder body 12, showing the positions of the first cooling passages 101 and the second cooling passages 102.
- the first cooling passages 101 are formed next to the depressed portions 70 to 77.
- the second cooling passages 102 are formed next to the connecting portion between the first cylinder 31 and the second cylinder 32 and the connecting portion between the second cylinder 32 and the third cylinder 33.
- FIG. 12 is a plan view of a cylinder body (reference example) having no depressed portions 70 to 77 along the outer contour 35 of the water jacket 12W. Where the depressed portions 70 to 77 are absent, the width K1 is large in the vicinity of the boundary 3612 between the inner contour 361 and the inner contour 362 and in the vicinity of the boundary 3623 between the inner contour 362 and the inner contour 363, but the width K2 is small in other areas.
- cooling passages can be provided only in the vicinity of the boundary 3612 and in the vicinity of the boundary 3623. Cooling passages can be provided next to only the connecting portion between the first cylinder 31 and the second cylinder 32 and the connecting portion between the second cylinder 32 and the third cylinder 33.
- the outer contour 35 of the water jacket 12W has the depressed portions 70 to 77. Therefore, the width K3 of the water jacket 12W is large in the vicinity of the depressed portions 70 to 77.
- the temperature of the mold 112 is likely to be particularly high at the connecting portion between the first cylinder 31 and the second cylinder 32 and the connecting portion between the second cylinder 32 and the third cylinder 33.
- the first cooling passages 101 and the second cooling passages 102 are provided in the vicinity of the connecting portion between the first cylinder 31 and the second cylinder 32 and in the vicinity of the connecting portion between the second cylinder 32 and the third cylinder 33. According to the present embodiment, it is possible to effectively cool portions that are likely to be particularly hot during the molding process. Therefore, it is possible to desirably mold the cylinder body 12.
- the depressed portions 70 to 77 are provided in the vicinity of all of the holes 41 to 44 into which the bolts 29 are inserted to fasten together the cylinder body 12 and the cylinder head 13.
- the depressed portions of the outer contour 35 do not always need to be provided in the vicinity of all of the holes 41 to 44.
- the depressed portions of the outer contour 35 may be provided in the vicinity of only some of the holes.
- the length N1 of the first straight line L1 between the cylinder 31 and the water jacket 12W is longer than the length N2 thereof between the first hole 41 and the water jacket 12W as the cylinder body 12 is seen along the cylinder axial line 31c as shown in FIG. 5 .
- N1 may be equal to N2.
- N1 may be shorter than N2.
- the contour 55 of the bottom portion of the water jacket 12W has the outer curve portion 55a and the inner curve portion 55b, and the curvature of the outer curve portion 55a is smaller than the curvature of the inner curve portion 55b.
- the curvature of the outer curve portion 55a may be equal to the curvature of the inner curve portion 55b.
- the curvature of the outer curve portion 55a may be larger than the curvature of the inner curve portion 55b.
- the engine 10 is a multi-cylinder engine including three cylinders 31 to 33.
- the number of cylinders of the engine 10 is not limited to three.
- the number of cylinders may be two or four or more.
- the engine 10 may be a single-cylinder engine including only one cylinder.
- the motorcycle 1 is an example of a straddled vehicle.
- a straddled vehicle refers to a vehicle that is straddled by a passenger.
- the straddled vehicle is not limited to the motorcycle 1.
- the straddled vehicle may be an auto tricycle, an ATV (All Terrain Vehicle), or a snowmobile.
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Description
- The present invention relates to a method for manufacturing an internal combustion engine having a water jacket through which coolant passes, particularly for a straddled vehicle.
- Internal combustion engines including a cylinder body having a cylinder, a cylinder head that defines a combustion chamber together with the cylinder, and bolts that fasten together the cylinder head and the cylinder body, have been known in the art. A water-cooled internal combustion engine includes a water jacket through which a coolant flows and which is formed in a portion of the cylinder body around the cylinder (see, for example,
JP2011-167706A (Honda Motor Co Ltd -
FIG. 13 is a partial cross-sectional view schematically showing an example of a conventional water-cooled internal combustion engine.Designations cylinder body 201 includes acylinder 204, and awater jacket 205 is formed in a portion of thecylinder body 201 around thecylinder 204. Apiston 206 is arranged inside thecylinder 204. Thecylinder head 202, thecylinder 204 and thepiston 206 together define acombustion chamber 207. - Although not shown in
FIG. 13 , a gasket is interposed between thecylinder head 202 and thecylinder body 201. Since thecylinder head 202 and thecylinder body 201 are fastened together by thebolts 203, thecylinder body 201 is in close contact with thecylinder head 202 with the gasket therebetween. The portion of thecylinder body 201 around thecylinder 204 is under a pressure (hereinafter referred to as the surface pressure) from thecylinder head 202. - An internal combustion engine repeatedly goes through a cycle of intake, compression, combustion and exhaust. During the combustion stroke, the mixture combusts in the
combustion chamber 207. This combustion creates a force on thecylinder head 202 in the direction away from the cylinder body 201 (upward inFIG. 13 ). In other words, thecylinder head 202 is under a force such as to lift thecylinder head 202 off thecylinder body 201. During the process, the surface pressure applied to the portion around thecylinder 204 fluctuates. In order to suppress the fluctuation of the surface pressure, there is a need to increase the fastening force of thebolts 203. However, in order to increase the fastening force of thebolts 203, thebolts 203 need to be designed to have a structure such that it is possible to endure the increased fastening force by, for example, increasing the thickness of thebolts 203, and it is necessary to ensure a sufficient thickness of thecylinder body 201 and thecylinder head 202. As a result, it may lead to an increase in cost and size of the internal combustion engine. - Engines with depressed portions depressed in a direction radially outward of the cylinder are known from
EP 2 131 031 A1CN 102 352 799 A - An object of at least one embodiment of at least one aspect of the present invention may be to obviate or at least mitigate one or more problems and/or disadvantages in the prior art.
- An object of at least one embodiment of at least one aspect of the present invention may be to seek to provide an internal combustion engine including a water jacket formed in a portion of the cylinder body around the cylinder, wherein it may be possible to suppress an increase in cost and size of the internal combustion engine by suppressing the fluctuation of the surface pressure applied to the portion around the cylinder.
- According to the present invention there is provided a method for manufacturing an internal combustion engine according to the appended claims.
- According to a first aspect of the present invention there is provided a method for manufacturing an internal combustion engine, wherein the internal combustion engine comprises:
- a cylinder body comprising a cylinder, a water jacket formed around the cylinder, a first hole that is formed outward of the water jacket in a radial direction of the cylinder and that extends parallel to an axial line of the cylinder;
- a cylinder head that comprises a hole extending on a center line of the first hole and that covers the cylinder; and
- a first bolt that is inserted into the first hole and the hole of the cylinder head to fasten together the cylinder head and the cylinder body, wherein:
- as the cylinder body is seen along the axial line of the cylinder, the cylinder body comprises an outer contour that defines an outer side of the water jacket in the radial direction of the cylinder, an inner contour that defines an inner side of the water jacket in the radial direction of the cylinder, a first opposing surface that is located outward of the outer contour in the radial direction of the cylinder and that opposes the cylinder head, and a second opposing surface that is located inward of the inner contour in the radial direction of the cylinder and that opposes the cylinder head; and
- as the cylinder body is seen along the axial line of the cylinder, the outer contour comprises a first depressed portion that is located radially outward of the first hole and that is depressed in a direction radially outward of the cylinder, the method comprising:
- preparing a mold comprising a water jacket molding portion that has the same shape as the water jacket and that comprises a cooling passage formed therein;
- injecting a metal material into the mold; and
- supplying a coolant to flow through the cooling passage, thereby cooling the mold.
- The first depressed portion of the cylinder body may be formed next to the cooling passage of the water jacket molding portion.
- According to a second aspect of the present invention there is provided a method for manufacturing an internal combustion engine, wherein the internal combustion engine comprises:
- a cylinder body comprising a cylinder, a water jacket formed around the cylinder, a first hole that is formed outward of the water jacket in a radial direction of the cylinder and that extends parallel to an axial line of the cylinder;
- a cylinder head that comprises a hole extending on a center line of the first hole and that covers the cylinder; and
- a first bolt that is inserted into the first hole and the hole of the cylinder head to fasten together the cylinder head and the cylinder body, wherein:
- as the cylinder body is seen along the axial line of the cylinder, the cylinder body comprises an outer contour that defines an outer side of the water jacket in the radial direction of the cylinder, an inner contour that defines an inner side of the water jacket in the radial direction of the cylinder, a first opposing surface that is located outward of the outer contour in the radial direction of the cylinder and that opposes the cylinder head, and a second opposing surface that is located inward of the inner contour in the radial direction of the cylinder and that opposes the cylinder head; and
- as the cylinder body is seen along the axial line of the cylinder, the outer contour comprises a first depressed portion that is located radially outward of the first hole and that is depressed in a direction radially outward of the cylinder, wherein
- the cylinder body comprises another cylinder that extends parallel to the cylinder, and a third hole that extends parallel to the axial line of the cylinder;
- the internal combustion engine comprises a third bolt that is inserted through the third hole to fasten together the cylinder head and the cylinder body;
- as the cylinder body is seen along the axial line of the cylinder, a straight line passes through between the first hole and the second hole, wherein the straight line passes through the center of the cylinder and is perpendicular to a straight line that passes through the center of the cylinder and a center of the other cylinder;
- as the cylinder body is seen along the axial line of the cylinder, a straight line passes through between the second hole and the third hole, wherein the straight line passes through the center of the other cylinder and is perpendicular to the straight line that connects between the center of the cylinder and the center of the other cylinder;
- the water jacket is formed around the cylinder and the other cylinder; and
- as the cylinder body is seen along the axial line of the cylinder, the outer contour includes a third depressed portion that is located radially outward of the third hole and is depressed in a direction radially outward of the other cylinder, the method comprising:
- preparing a mold comprising a water jacket molding portion that has the same shape as the water jacket and that comprises a first cooling passage and a second cooling passage formed therein;
- injecting a metal material into the mold; and
- supplying a coolant to flow through the first cooling passage and the second cooling passage, thereby cooling the mold, wherein:
- the first depressed portion of the cylinder body is formed next to the first cooling passage of the water jacket molding portion; and
- a connecting portion between the cylinder and the other cylinder is formed next to the second cooling passage of the water jacket molding portion.
- According to an implementation of the present invention there is provided an internal combustion engine manufactured by the method of the first or second aspect of the present invention.
- With the internal combustion engine described above, the surface of the cylinder body that opposes the cylinder head may comprise the first opposing surface on the outer side relative to the water jacket and the second opposing surface on the inner side relative to the water jacket. Since the first bolt fastens the cylinder head to the cylinder body, the first opposing surface and the second opposing surface may be under a pressure from the cylinder head. With the internal combustion engine described above, the provision of the first depressed portion may decrease the volume of a portion of the first opposing surface in the vicinity of the first hole and accordingly may decrease the rigidity thereof, as compared with a case where the first depressed portion is absent. Therefore, in the vicinity of the first hole, the rigidity of the second opposing surface may be (relatively) higher than the rigidity of the first opposing surface. In the vicinity of the first hole, the surface pressure between the first opposing surface and the cylinder head may be lower while the surface pressure between the second opposing surface and the cylinder head may be higher. Therefore, it may be possible to suppress the fluctuation of the surface pressure applied to the portion of the cylinder body around the cylinder during the combustion of the mixture. Thus, it may be possible to suppress an increase in cost and size of the internal combustion engine.
- According to one preferred implementation the cylinder body may comprise a second hole that may be formed outward of the water jacket in the radial direction of the cylinder and that may extend parallel to the axial line of the cylinder. The internal combustion engine may comprise a second bolt that may be inserted into the second hole to fasten together the cylinder head and the cylinder body. As the cylinder body is seen along the axial line of the cylinder, the outer contour may comprise a second depressed portion that may be located radially outward of the second hole and/or that may be depressed in a direction radially outward of the cylinder. As the cylinder body is seen along the axial line of the cylinder, the inner contour may comprise an arc that may be centered at a center of the cylinder and that may have a first curvature. As the cylinder body is seen along the axial line of the cylinder, a portion of the outer contour between the first depressed portion and the second depressed portion may comprise an arc whose center may be off the center of the cylinder, and that may have a second curvature smaller than the first curvature.
- According to the implementation described above, the width of the water jacket may be larger and/or the area of the first opposing surface may be smaller, as compared with a case where a portion of the water jacket between the first depressed portion and/or the second depressed portion of the outer contour may be an arc that may be centered at the center of the cylinder. Therefore, the rigidity of the second opposing surface may be relatively high/higher than the rigidity of the first opposing surface. The surface pressure between the first opposing surface and the cylinder head may be lower while the surface pressure between the second opposing surface and the cylinder head may be higher. This further suppresses the fluctuation of the surface pressure applied to the portion of the cylinder body around the cylinder during the combustion of the mixture. Thus, it may be possible to further suppress an increase in cost and size of the internal combustion engine.
- According to one preferred implementation, as the cylinder body is seen along the axial line of the cylinder, an entirety of a portion of the outer contour between the first depressed portion and the second depressed portion may be an arc whose center may be off the center of the cylinder, and that may have a second curvature smaller than the first curvature.
- According to the implementation described above, the area of the second opposing surface may increase and the rigidity of the second opposing surface may become relatively higher. Therefore, the surface pressure between the second opposing surface and the cylinder head may further increase. This may further suppress the fluctuation of the surface pressure applied to the portion of the cylinder body around the cylinder during the combustion of the mixture. Thus, it may be possible to further suppress an increase in cost and size of the internal combustion engine.
- According to one preferred implementation, as the cylinder body is seen along the axial line of the cylinder, an angle between a first straight line, which may connect between the center of the cylinder and the center of the first hole, and a second straight line that may connect between the center of the cylinder and a point along the first depressed portion that may be farthest away from the center of the cylinder may be 5° to 15°.
- According to the implementation described above, the first depressed portion may be provided in the vicinity of the first hole into which the first bolt may be inserted. The advantageous effects described above may be pronounced as compared with a case where the first depressed portion may be provided far away from the first hole.
- According to one preferred implementation, as the cylinder body is seen along the axial line of the cylinder, a length, between the cylinder and the water jacket, of a first straight line that connects between the center of the cylinder and the center of the first hole may be longer than a length, between the first hole and the water jacket, of the first straight line.
- According to the implementation described above, the area of the second opposing surface may be large in the vicinity of the first hole. In the vicinity of the first hole, the rigidity of the second opposing surface may be high, thereby increasing the surface pressure between the second opposing surface and the cylinder head. This may further suppress the fluctuation of the surface pressure applied to the portion of the cylinder body around the cylinder during the combustion of the mixture. Thus, it may be possible to further suppress an increase in cost and size of the internal combustion engine.
- According to one preferred implementation, on a cross-section of the cylinder body that comprises the center line of the cylinder and the center line of the first hole, a contour of a bottom portion of the water jacket may comprise an outer curve portion that may be located on a side of the first hole and an inner curve portion that may be located on a side of the cylinder. A curvature of the outer curve portion may be smaller than a curvature of the inner curve portion.
- Since the first bolt may be inserted into the first hole, a portion of the cylinder body close to the first hole may be bound by the first bolt. During the combustion of the mixture, a large local stress may occur on the portion close to the first hole. According to the embodiment described above, however, the curve (outer curve portion) of a portion of the bottom portion of the water jacket that may be close to the first hole may be more gentle than the curve (inner curve portion) of a portion thereof that may be close to the cylinder. Therefore, it may be possible to reduce the stress on the portion of the bottom portion of the water jacket that may be close to the first hole. Thus, it may be possible to improve the durability of the cylinder body.
- According to one preferred implementation, the cylinder body may comprise another cylinder that may extend parallel to the cylinder, and a third hole that may extend parallel to the axial line of the cylinder. The internal combustion engine may comprise a third bolt that may be inserted into the third hole to fasten together the cylinder head and the cylinder body. As the cylinder body is seen along the axial line of the cylinder, a straight line may pass through between the first hole and the second hole, wherein the straight line may pass through the center of the cylinder and/or may be perpendicular to a straight line that may pass through the center of the cylinder and/or a center of the other cylinder. As the cylinder body is seen along the axial line of the cylinder, a straight line may pass through between the second hole and the third hole, wherein the straight line may pass through the center of the other cylinder and/or may be perpendicular to the straight line that connects between the center of the cylinder and the center of the other cylinder. The water jacket may be formed around the cylinder and/or the other cylinder. As the cylinder body is seen along the axial line of the cylinder, the outer contour may comprise a third depressed portion that may be located radially outward of the third hole and/or may be depressed in a direction radially outward of the other cylinder.
- According to the implementation described above, the advantageous effect(s) described above can be realized for a multi-cylinder internal combustion engine.
- According to an implementation of the present invention there is provided a straddled vehicle comprising an internal combustion engine according to the aforementioned implementation of the present invention. The straddled vehicle may comprise a driving wheel that may be linked to the internal combustion engine with a power transmitting member therebetween and/or that may be driven by the internal combustion engine.
- With the straddled vehicle described above, the advantageous effect(s) described above can be realized for an internal combustion engine for driving the driving wheel.
- With the manufacturing method according to the first aspect of the present invention described above, a coolant may be supplied to flow through the cooling passage during the molding process, thereby desirably cooling the mold. Therefore, it may be possible to reliably prevent the mold from being burnt, and/or it may be possible to realize a high-quality cylinder body.
- According to one preferred embodiment, the first depressed portion of the cylinder body may be formed next to the cooling passage of the water jacket molding portion.
- According to the embodiment described above, it may be possible to increase the width of the water jacket molding portion for the presence of the first depressed portion. Thus, it may be possible to ensure a sufficient space for the cooling passage. The cooling passage can be formed in the water jacket molding portion without imposing design restrictions.
- With the manufacturing method according to the second aspect of the present invention described above, it may be possible to increase the width of the water jacket molding portion for the presence of the first depressed portion. Thus, it may be possible to ensure a space for the first cooling passage. The first cooling passage can be formed in the water jacket molding portion without imposing design restrictions. With a multi-cylinder internal combustion engine, the connecting portion between cylinders is not easily cooled and is likely to be hot during the molding process. According to the embodiment described above, however, since the second cooling passage is formed next to the connecting portion between cylinders in the water jacket molding portion, it is possible to effectively cool the connecting portion. Therefore, it may be possible to reliably prevent the mold from being burnt, and/or it may be possible to realize a high-quality cylinder body.
- According to the present invention it may be possible to provide an internal combustion engine comprising a water jacket formed in a portion of the cylinder body around the cylinder, wherein it may be possible to suppress an increase in cost and size of the internal combustion engine by suppressing the fluctuation of the surface pressure applied to the portion around the cylinder.
- An embodiment of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, which are:
- FIG. 1
- a side view of a motorcycle according to an implementation of the present invention;
- FIG. 2
- a cross-sectional view of a portion of an internal combustion engine;
- FIG. 3
- a cross-sectional view of a portion of a cylinder body and a cylinder head;
- FIG. 4
- a plan view of the cylinder body;
- FIG. 5
- a plan view of the cylinder body;
- FIG. 6
- a cross-sectional view of the cylinder body and the cylinder head taken along line VI-VI of
FIG. 4 ; - FIG. 7
- an enlarged cross-sectional view of a portion of the cylinder body;
- FIG. 8
- a plan view of a gasket;
- FIG. 9
- a perspective view of a mold used for manufacturing the cylinder body;
- FIG. 10
- a perspective view drawn so that cooling passages formed inside the mold are visible;
- FIG. 11
- a plan view of the cylinder body with cooling passages drawn;
- FIG. 12
- a plan view of a cylinder body according to a reference example; and
- FIG. 13
- a partial cross-sectional view schematically showing an example of a conventional internal combustion engine.
- An implementation of the present invention will now be described with reference to the accompanying drawings.
FIG. 1 is a side view of amotorcycle 1, which is an example of a straddled vehicle. Themotorcycle 1 includes afront wheel 2, arear wheel 3, an internal combustion engine (hereinafter referred to as "the engine") 10, a handle 4, a fuel tank 5, and aseat 6. Theengine 10 is linked to therear wheel 3 by a power transmitting member such as achain 7. Therear wheel 3 is a driving wheel that is driven by theengine 10. - As shown in
FIG. 2 , theengine 10 ha acrankcase 11, acylinder body 12 connected to thecrankcase 11, acylinder head 13 connected to thecylinder body 12, and acylinder head cover 14 connected to thecylinder head 13. Theengine 10 is a multi-cylinder engine. In the present embodiment, theengine 10 is a three-cylinder engine having afirst cylinder 31, asecond cylinder 32 and athird cylinder 33. - The
cylinder head 13 is provided with anignitor 16, an intake valve (not shown) and anexhaust valve 18. The first tothird cylinders 31 to 33 are provided inside thecylinder body 12. Apiston 19 is accommodated inside each of thecylinders 31 to 33. Thecylinder head 13, thecylinders 31 to 33 and thepistons 19 together define a combustion chamber 58. Thepiston 19 is linked to acrankshaft 21 by a connectingrod 20. Thecrankshaft 21 is arranged inside thecrankcase 11. Thecrankshaft 21 extends in a vehicle width direction. Agenerator 22 is attached to a left end portion of thecrankshaft 21. Asprocket 23 is attached to a right end portion of thecrankshaft 21. Acam chain 24 is wound around thesprocket 23. Thecam chain 24 is also wound around asprocket 26 attached to acamshaft 25. - The
engine 10 is a water-cooled engine. As shown inFIG. 3 , thecylinder body 12 haswater jackets cylinder head 13 also has awater jacket 13W through which the coolant passes. Agasket 28 is interposed between thecylinder body 12 and thecylinder head 13. As will be described later, thegasket 28 has a plurality ofholes FIG. 8 ). Thewater jacket 12W of thecylinder body 12 and thewater jacket 13W of thecylinder head 13 communicate with each other through theholes gasket 28. -
FIG. 4 andFIG. 5 are plan views of thecylinder body 12. Specifically, these figures show thecylinder body 12 as seen along the axial line (hereinafter referred to as the "cylinder axial line") 31c of thefirst cylinder 31. In the following description, "as shown inFIG. 4 " and "as shown inFIG. 5 " mean that thecylinder body 12 is seen along the first cylinderaxial line 31c. Note that since the first tothird cylinders 31 to 33 are arranged parallel to each other, the axial line of thesecond cylinder 32 and the axial line of thethird cylinder 33 are parallel to the cylinderaxial line 31c of thefirst cylinder 31. - As shown in
FIG. 4 , thewater jacket 12W is formed around thefirst cylinder 31, thesecond cylinder 32 and thethird cylinder 33. Thewater jacket 12W has a firstwater jacket portion 31W around thefirst cylinder 31, a secondwater jacket portion 32W around thesecond cylinder 32, and a thirdwater jacket portion 33W around thethird cylinder 33. The firstwater jacket portion 31W is connected to the secondwater jacket portion 32W, and the secondwater jacket portion 32W is connected to the thirdwater jacket portion 33W. - The
water jacket 12W is defined by anouter contour 35 and aninner contour 36. Theouter contour 35 has a firstouter contour 351 that defines the outer side of the firstwater jacket portion 31W in the radial direction of thefirst cylinder 31, a secondouter contour 352 that defines the outer side of the secondwater jacket portion 32W in the radial direction of thesecond cylinder 32, and a thirdouter contour 353 that defines the outer side of the thirdwater jacket portion 33W in the radial direction of thethird cylinder 33. Theinner contour 36 has a firstinner contour 361 that defines the inner side of the firstwater jacket portion 31W in the radial direction of thefirst cylinder 31, a secondinner contour 362 that defines the inner side of the secondwater jacket portion 32W in the radial direction of thesecond cylinder 32, and a thirdinner contour 363 that defines the inner side of the thirdwater jacket portion 33W in the radial direction of thethird cylinder 33. Note thatdesignation 3512 denotes a boundary between the firstouter contour 351 and the secondouter contour 352.Designation 3523 denotes a boundary between the secondouter contour 352 and the thirdouter contour 353.Designation 3612 denotes a boundary between the firstinner contour 361 and the secondinner contour 362.Designation 3623 denotes a boundary between the secondinner contour 362 and the thirdinner contour 363. - The
cylinder body 12 has first tofourth holes 41 to 44 into which bolts 29 (seeFIG. 6 ) for fastening together thecylinder head 13 and thecylinder body 12 are inserted. The first tofourth holes 41 to 44 extend parallel to the cylinderaxial line 31c. As shown inFIG. 6 , thecylinder head 13 has asecond hole 42A that corresponds to thesecond hole 42 of thecylinder body 12, and athird hole 43A that corresponds to thethird hole 43 of thecylinder body 12. Abolt 29 is inserted into thesecond hole 42 of thecylinder body 12 and thesecond hole 42A of thecylinder head 13. Similarly, abolt 29 is inserted into thethird hole 43 of thecylinder body 12 and thethird hole 43A of thecylinder head 13. Although not shown in the figure, thecylinder head 13 has a first hole that corresponds to thefirst hole 41 of thecylinder body 12, and a fourth hole that corresponds to thefourth hole 44 of thecylinder body 12. Abolt 29 is inserted into thefirst hole 41 of thecylinder body 12 and the first hole of thecylinder head 13. Abolt 29 is inserted into thefourth hole 44 of thecylinder body 12 and the fourth hole of thecylinder head 13. Thecylinder head 13 and thecylinder body 12 are fastened together by thesebolts 29. Note that thepiston 19 is not shown inFIG. 6 . - As shown in
FIG. 4 , a straight line that passes throughcenters 31c to 33c of the first tothird cylinders 31 to 33 is denoted as L3. A straight line that passes through thecenter 31c of thefirst cylinder 31 and is perpendicular to the straight line L3 is denoted as L11. A straight line that passes through thecenter 32c of thesecond cylinder 32 and is perpendicular to the straight line L3 is denoted as L12. Then, the straight line L11 passes through between thefirst hole 41 and thesecond hole 42. The straight line L12 passes through between thesecond hole 42 and thethird hole 43. - As shown in
FIG. 4 , thecylinder body 12 has a first opposingsurface 51 that is located outward of theouter contour 35 in the radial direction of thefirst cylinder 31, and a second opposingsurface 52 that is located inward of theinner contour 36 in the radial direction of thefirst cylinder 31. The first opposingsurface 51 has an opposingsurface 511 that is located outward of the firstouter contour 351 in the radial direction of thefirst cylinder 31, an opposingsurface 512 that is located outward of the secondouter contour 352 in the radial direction of thesecond cylinder 32, and an opposingsurface 513 that is located outward of the thirdouter contour 353 in the radial direction of thethird cylinder 33. The second opposingsurface 52 has an opposing surface 521 that is located inward of the firstinner contour 361 in the radial direction of thefirst cylinder 31, an opposingsurface 522 that is located inward of the secondinner contour 362 in the radial direction of thesecond cylinder 32, and an opposingsurface 523 that is located inward of the thirdinner contour 363 in the radial direction of thethird cylinder 33. As shown inFIG. 6 , the first opposingsurface 51 and the second opposingsurface 52 oppose thecylinder head 13. Herein, thegasket 28 is interposed between thecylinder head 13 and thecylinder body 12. The first opposingsurface 51 and the second opposingsurface 52 oppose thecylinder head 13 with thegasket 28 therebetween. As used herein, "opposing the cylinder head" means both directly opposing the cylinder head and indirectly opposing the cylinder head with a gasket, or the like, therebetween. - Next, the shapes of the
outer contour 35 and theinner contour 36 of thewater jacket 12W will be described in detail. - As shown in
FIG. 4 , theouter contour 35 has depressedportions first cylinder 31. Thedepressed portion 71 is located radially outward of thefirst hole 41 and is depressed in the direction radially outward of thefirst cylinder 31. Thedepressed portion 72 is located radially outward of thesecond hole 42 and is depressed in the direction radially outward of thefirst cylinder 31. Theouter contour 35 has depressedportions second cylinder 32, anddepressed portions third cylinder 33. Thedepressed portion 73 is located radially outward of thesecond hole 42 and is depressed in the direction radially outward of thesecond cylinder 32. Thedepressed portion 74 is located radially outward of thethird hole 43 and is depressed in the direction radially outward of thesecond cylinder 32. Thedepressed portion 75 is located radially outward of thethird hole 43 and is depressed in the direction radially outward of thethird cylinder 33. Thedepressed portions fourth hole 44 and are depressed in the direction radially outward of thethird cylinder 33. Note that in the following description, thedepressed portions - As the
cylinder body 12 is seen along the cylinderaxial line 31c, the center of thecylinder 31 coincides with the cylinderaxial line 31c. Therefore, in the following description, thesame designation 31c as the cylinder axial line will be used for the center of thecylinder 31. As shown inFIG. 5 , a straight line that connects between the center 31c of thecylinder 31 and acenter 41c of thefirst hole 41 is denoted as a first straight line L1. A straight line that connects between the center 31c of thecylinder 31 and a point along the firstdepressed portion 71 that is farthest away from thecenter 31c of thecylinder 31 is denoted as a second straight line L2. In the present embodiment, the angle θ between the first straight line L1 and the second straight line L2 is 5° to 15°. The firstdepressed portion 71 is provided in the vicinity of thefirst hole 41. Note, however, that the value of the angle θ above is merely an example, and there is no particular limitation thereto. - As shown in
FIG. 4 , the firstinner contour 361 is an arc 37a that is centered at thecenter 31c of thecylinder 31 and that has a first curvature. While the arc 37a may be only a portion of the firstinner contour 361, the arc 37a is herein the entirety of the firstinner contour 361. - A portion of the first
outer contour 351 between the firstdepressed portion 71 and the seconddepressed portion 72 is anarc 38a whosecenter 39c is off thecenter 31c of thecylinder 31, and that has a second curvature smaller than the first curvature. For example, in the upper half ofFIG. 4 , thearc 38a of the firstouter contour 351 is located upward of the arc 37a of the firstinner contour 361, and thecenter 39c of thearc 38a is located downward of thecenter 31c of the arc 37a. While thearc 38a may be only a portion of the firstouter contour 351 that is between the firstdepressed portion 71 and the seconddepressed portion 72, thearc 38a is herein the entirety of the firstouter contour 351 between the firstdepressed portion 71 and the seconddepressed portion 72. - The positional relationship between the second
inner contour 362 and the secondouter contour 352 and the positional relationship between the thirdinner contour 363 and the thirdouter contour 353 are similar to the positional relationship between the firstinner contour 361 and the firstouter contour 351. A portion or whole of the secondinner contour 362 is anarc 37b that is centered at thecenter 32c of thesecond cylinder 32 and that has the first curvature. A portion or whole of the thirdinner contour 363 is anarc 37c that is centered at thecenter 33c of thethird cylinder 33 and that has the first curvature. A portion or whole of the secondouter contour 352 between thedepressed portion 73 and thedepressed portion 74 is anarc 38b whose center is off thecenter 32c of thesecond cylinder 32 and that has the second curvature. A portion or whole of the thirdouter contour 353 between thedepressed portion 75 and thedepressed portion 76 is anarc 38c whose center is off thecenter 33c of thethird cylinder 33 and that has the second curvature. - As shown in
FIG. 5 , the length N1 of the first straight line L1 between thefirst cylinder 31 and thewater jacket 12W is longer than the length N2 thereof between thefirst hole 41 and thewater jacket 12W. In the vicinity of thefirst hole 41, the area of the second opposingsurface 52 is relatively large. -
FIG. 7 is a partial cross-sectional view of thecylinder body 12 taken along the first straight line L1. On a cross-section of thecylinder body 12 that includes the first straight line L1, acontour 55 of the bottom portion of thewater jacket 12W has anouter curve portion 55a that is located on the side of thefirst hole 41 and aninner curve portion 55b that is located on the side of thefirst cylinder 31. Theouter curve portion 55a is more gently curved than theinner curve portion 55b. The curvature of theouter curve portion 55a is smaller than the curvature of theinner curve portion 55b. Note that the curvature of theouter curve portion 55a and the curvature of theinner curve portion 55b may each be constant or not constant. Where the curvature of theouter curve portion 55a and the curvature of theinner curve portion 55b are not constant, they refer to the mean curvature of theouter curve portion 55a and the mean curvature of theinner curve portion 55b. -
FIG. 8 is a plan view of thegasket 28. Thegasket 28 hasholes 31h to 33h that correspond to the first tothird cylinders 31 to 33, and first tofourth holes 41h to 44h into which thebolts 29 are inserted. Thegasket 28 also has theholes hole 28a is arranged over thewater jacket 121 of thecylinder body 12. Theholes 28b are arranged over thewater jacket 12W of thecylinder body 12. The coolant in thewater jacket 121 flows into thewater jacket 13W of the cylinder head 13 (see an arrow inFIG. 3 ) through thehole 28a. The coolant in thewater jacket 13W flows into thewater jacket 12W of the cylinder body 12 (see arrows inFIG. 3 ) through theholes 28b. Thecylinder body 12 and thecylinder head 13 are cooled by the coolant flowing through thewater jacket 121, thewater jacket 13W and thewater jacket 12W in this order. - The
engine 10 is configured as described above. As described above, thecylinder head 13 is fastened to thecylinder body 12 by the bolts 29 (seeFIG. 6 ). The first opposingsurface 51 and the second opposingsurface 52 of thecylinder body 12 are pressed against thecylinder head 13. The first opposingsurface 51 and the second opposingsurface 52 are under a pressure from the cylinder head 13 (hereinafter referred to as the surface pressure). Theengine 10 repeatedly goes through a cycle of intake, compression, combustion and exhaust. During the combustion stroke, the mixture of fuel and air combusts in the combustion chamber 58. This combustion creates a force such as to lift thecylinder head 13 off thecylinder body 12. During this process, the surface pressure applied to the first opposingsurface 51 and the second opposingsurface 52 fluctuates. One possible way to suppress the fluctuation of the surface pressure is to increase the fastening force of thebolts 29. However, in order to increase the fastening force of thebolts 29, thecylinder body 12 and thecylinder head 13 need to be designed so that they can endure such an increased fastening force. Without some countermeasures, this will lead to an increase in cost and size of theengine 10. - According to the present implementation, however, the
outer contour 35 of thewater jacket 12W has thedepressed portions 70 to 77 as thecylinder body 12 is seen along the cylinderaxial line 31c as shown inFIG. 4 . Theouter contour 35 of thewater jacket 12W is partially depressed in the vicinity of the first tofourth holes 41 to 44 into which thebolts 29 are inserted. Therefore, as compared with a case where thedepressed portions 70 to 77 are absent, the area of the first opposingsurface 51 is smaller in the vicinity of the first tofourth holes 41 to 44. In the vicinity of the first tofourth holes 41 to 44, the ratio of the area of the second opposingsurface 52 with respect to the total area of the first opposingsurface 51 and the second opposingsurface 52 is larger as compared with a case where thedepressed portions 70 to 77 are absent. Therefore, with theengine 10 according to the present embodiment, the rigidity of the second opposingsurface 52 is relatively larger than the rigidity of the first opposingsurface 51. Thus, the surface pressure between the first opposingsurface 51 and thecylinder head 13 decreases, but the surface pressure between the second opposingsurface 52 and thecylinder head 13 increases. Therefore, it is possible to suppress the fluctuation of the surface pressure applied to portions of thecylinder body 12 around the first tothird cylinders 31 to 33 during the combustion of the mixture. According to the present implementation, since it is possible to suppress the fluctuation of the surface pressure of thecylinder body 12, there is no need to increase the fastening force of thebolts 29 as compared with conventional techniques. A fastening force of thebolts 29 similar to those of conventional techniques is sufficient. Therefore, it is possible to suppress an increase in cost and size of theengine 10. - According to the present implementation, a portion of the
outer contour 35 of thewater jacket 12W between the firstdepressed portion 71 and the seconddepressed portion 72 is thearc 38a whosecenter 39c is off thecenter 31c of thecylinder 31 as thecylinder body 12 is seen along the cylinderaxial line 31c as shown inFIG. 4 . Moreover, the curvature of thearc 38a (the second curvature) is smaller than the curvature of the arc 37a of the inner contour 36 (the first curvature). Therefore, the width of thewater jacket 12W increases and the area of the first opposingsurface 51 decreases, as compared with a case where a portion of theouter contour 35 that is between the firstdepressed portion 71 and the seconddepressed portion 72 is an arc that is centered at thecenter 31c of thecylinder 31 and that has the first curvature. This further relatively increases the rigidity of the second opposingsurface 52 and further increases the surface pressure between the second opposingsurface 52 and thecylinder head 13. Therefore, it is possible to further suppress an increase in cost and size of theengine 10. - While there is no particular limitation on the position of the first
depressed portion 71 of theouter contour 35, the position is such that the angle θ is 5° to 15°, wherein θ is the angle between the first straight line L1 that connects between the center 31c of thefirst cylinder 31 and thecenter 41c of thefirst hole 41 and the second straight line L2 that connects between the center 31c of thefirst cylinder 31 and a point along the firstdepressed portion 71 that is farthest away from thecenter 31c of thefirst cylinder 31 as thecylinder body 12 is seen along the cylinderaxial line 31c as shown inFIG. 5 in the present embodiment. The provision of the firstdepressed portion 71 near thefirst hole 41 enhances the advantageous effects described above. Note that this similarly applies also to the otherdepressed portions - According to the present implementation, the length N1 of the first straight line L1 between the
first cylinder 31 and thewater jacket 12W is longer than the length N2 thereof between thefirst hole 41 and thewater jacket 12W as thecylinder body 12 is seen along the cylinderaxial line 31c as shown inFIG. 5 . In the vicinity of thefirst hole 41, the area of the second opposingsurface 52 is larger. This increase the rigidity of the second opposingsurface 52 and the surface pressure between the second opposingsurface 52 and thecylinder head 13 in the vicinity of thefirst hole 41. Therefore, it is possible to further suppress an increase in cost and size of theengine 10. Note that although the description is omitted, this similarly applies also to portions in the vicinity of theother holes 42 to 44. - According to the present implementation, as shown in
FIG. 7 , on a cross-section of thecylinder body 12 that includes the cylinderaxial line 31c and thecenter line 41c of thefirst hole 41, thecontour 55 of the bottom portion of thewater jacket 12W includes theouter curve portion 55a that is located on the side of thefirst hole 41 and theinner curve portion 55b that is located on the side of thefirst cylinder 31. Since thebolt 29 is inserted in thefirst hole 41, a portion of thecylinder body 12 that is close to thefirst hole 41 is bound by thebolt 29. During the combustion of the mixture, there may occur a large local stress on a portion that is close to thefirst hole 41. According to the present embodiment, however, the curvature of theouter curve portion 55a is smaller than the curvature of theinner curve portion 55b. The curve of a portion of the bottom portion of thewater jacket 12W that is close to thefirst hole 41 is more gentle than the curve of a portion thereof that is close to thecylinder 31. Therefore, it is possible to reduce the stress on the portion of the bottom portion of thewater jacket 12W that is close to thefirst hole 41. Thus, it is possible to improve the durability of thecylinder body 12. - The
engine 10 is manufactured by manufacturing thecylinder body 12 and thecylinder head 13, and fastening thecylinder body 12 and thecylinder head 13 together by thebolts 29. According to the invention the cylinder body can be manufactured as follows, for example. - First, a
mold 112 is prepared. As shown inFIG. 9 , themold 112 hascylinder molding portions 131 to 133 having the same shape as the first tothird cylinders 31 to 33, waterjacket molding portions water jackets hole molding portions 141 to 144 having the same shape as the first tofourth holes 41 to 44. Although not shown inFIG. 9 , cooling passages, through which a coolant such as water flows, are formed inside the waterjacket molding portion 112W and the bolthole molding portions 141 to 144.FIG. 10 is a perspective view drawn so that coolingpassages jacket molding portion 112W andcooling passages 103 formed inside the bolthole molding portions 141 to 144 are visible. In the following description, thecooling passages - When manufacturing the
cylinder body 12, themold 112 is prepared, and then a metal material is injected into themold 112. Note that there is no particular limitation on the metal material, and the metal material may be any of various metal materials known in the art, e.g. aluminium. Then, a coolant is supplied to flow through thecooling passages 101 to 103, thereby cooling themold 112 and the metal material. Note that as to when to start supplying the coolant through thecooling passages 101 to 103, it may be before, during or after the process of injecting a metal material into themold 112. Thus, it is possible to mold thecylinder body 12 while cooling themold 112. -
FIG. 11 is a plan view of thecylinder body 12, showing the positions of thefirst cooling passages 101 and thesecond cooling passages 102. Thefirst cooling passages 101 are formed next to thedepressed portions 70 to 77. Thesecond cooling passages 102 are formed next to the connecting portion between thefirst cylinder 31 and thesecond cylinder 32 and the connecting portion between thesecond cylinder 32 and thethird cylinder 33. - Now, in order to form cooling passages inside the
mold 112, there is a need for space for cooling passages. However, since the width of thewater jacket 12W is relatively small, the width of the waterjacket molding portion 112W is small.FIG. 12 is a plan view of a cylinder body (reference example) having nodepressed portions 70 to 77 along theouter contour 35 of thewater jacket 12W. Where thedepressed portions 70 to 77 are absent, the width K1 is large in the vicinity of theboundary 3612 between theinner contour 361 and theinner contour 362 and in the vicinity of theboundary 3623 between theinner contour 362 and theinner contour 363, but the width K2 is small in other areas. Therefore, when thedepressed portions 70 to 77 are absent, cooling passages can be provided only in the vicinity of theboundary 3612 and in the vicinity of theboundary 3623. Cooling passages can be provided next to only the connecting portion between thefirst cylinder 31 and thesecond cylinder 32 and the connecting portion between thesecond cylinder 32 and thethird cylinder 33. - According to the present embodiment, however, as shown in
FIG. 11 , theouter contour 35 of thewater jacket 12W has thedepressed portions 70 to 77. Therefore, the width K3 of thewater jacket 12W is large in the vicinity of thedepressed portions 70 to 77. Thus, it is possible not only to provide thesecond cooling passages 102 next to the connecting portion between thefirst cylinder 31 and thesecond cylinder 32 and the connecting portion between thesecond cylinder 32 and thethird cylinder 33, but also to provide thefirst cooling passages 101 in the vicinity of thedepressed portions 70 to 77. Thus, it is possible to increase the number of cooling passages. This increases the amount of the coolant that can be supplied during the molding process, allowing themold 112 to be cooled more effectively. According to the present embodiment, it is possible to more reliably prevent themold 112 from being burnt during the molding process. Therefore, it is possible to desirably mold thecylinder body 12. - Note that the temperature of the
mold 112 is likely to be particularly high at the connecting portion between thefirst cylinder 31 and thesecond cylinder 32 and the connecting portion between thesecond cylinder 32 and thethird cylinder 33. According to the present embodiment, however, thefirst cooling passages 101 and thesecond cooling passages 102 are provided in the vicinity of the connecting portion between thefirst cylinder 31 and thesecond cylinder 32 and in the vicinity of the connecting portion between thesecond cylinder 32 and thethird cylinder 33. According to the present embodiment, it is possible to effectively cool portions that are likely to be particularly hot during the molding process. Therefore, it is possible to desirably mold thecylinder body 12. - Although one embodiment has been described above, the embodiment described above is merely an example, and various other embodiments are possible.
- In the embodiment described above, the
depressed portions 70 to 77 are provided in the vicinity of all of theholes 41 to 44 into which thebolts 29 are inserted to fasten together thecylinder body 12 and thecylinder head 13. However, the depressed portions of theouter contour 35 do not always need to be provided in the vicinity of all of theholes 41 to 44. The depressed portions of theouter contour 35 may be provided in the vicinity of only some of the holes. - In the embodiment described above, the length N1 of the first straight line L1 between the
cylinder 31 and thewater jacket 12W is longer than the length N2 thereof between thefirst hole 41 and thewater jacket 12W as thecylinder body 12 is seen along the cylinderaxial line 31c as shown inFIG. 5 . However, there is no limitation thereto. N1 may be equal to N2. N1 may be shorter than N2. - In the embodiment described above, as shown in
FIG. 7 , thecontour 55 of the bottom portion of thewater jacket 12W has theouter curve portion 55a and theinner curve portion 55b, and the curvature of theouter curve portion 55a is smaller than the curvature of theinner curve portion 55b. However, there is no limitation thereto. The curvature of theouter curve portion 55a may be equal to the curvature of theinner curve portion 55b. The curvature of theouter curve portion 55a may be larger than the curvature of theinner curve portion 55b. - The
engine 10 according to the implementation described above is a multi-cylinder engine including threecylinders 31 to 33. However, the number of cylinders of theengine 10 is not limited to three. The number of cylinders may be two or four or more. Theengine 10 may be a single-cylinder engine including only one cylinder. - The
motorcycle 1 according to the implementation described above is an example of a straddled vehicle. A straddled vehicle refers to a vehicle that is straddled by a passenger. However, the straddled vehicle is not limited to themotorcycle 1. For example, the straddled vehicle may be an auto tricycle, an ATV (All Terrain Vehicle), or a snowmobile.REFERENCE SIGNS LIST 1 Motorcycle (straddled vehicle) 55 Contour of bottom portion of water jacket 3 Rear wheel (driving wheel) 55a Outer curve portion 7 Chain (power transmitting member) 55b Inner curve portion 10 Internal combustion engine 71 First depressed portion 12 Cylinder body 72 Second depressed portion 12W Water jacket 74 Third depressed portion 13 Cylinder head 101 First cooling passage 29 Bolt 102 Second cooling passage 31 First cylinder (cylinder) 112 Mold 32 Second cylinder (another cylinder) 112W Water jacket molding portion 35 Outer contour 36 Inner contour 37a Arc having first curvature 38a Arc having second curvature 41 First hole 42 Second hole 43 Third hole 51 First opposing surface 52 Second opposing surface
Claims (3)
- A method for manufacturing an internal combustion engine (10), wherein the internal combustion engine comprises:a cylinder body (12) comprising a cylinder (31), a water jacket (12W) formed around the cylinder (31), a first hole (41) that is formed outward of the water jacket (12W) in a radial direction of the cylinder (31) and that extends parallel to an axial line (31c) of the cylinder (31);a cylinder head (13) that comprises a hole extending on a center line (41c) of the first hole (41) and that covers the cylinder (31); anda first bolt (29) that is inserted into the first hole (41) and the hole of the cylinder head (13) to fasten together the cylinder head (13) and the cylinder body (12), wherein:as the cylinder body (12) is seen along the axial line (31c) of the cylinder (31), the cylinder body (12) comprises an outer contour (35) that defines an outer side of the water jacket (12W) in the radial direction of the cylinder (31), an inner contour (36) that defines an inner side of the water jacket (12W) in the radial direction of the cylinder (31), a first opposing surface (51) that is located outward of the outer contour (35) in the radial direction of the cylinder (31) and that opposes the cylinder head (13), and a second opposing surface (52) that is located inward of the inner contour (36) in the radial direction of the cylinder (31) and that opposes the cylinder head (13); andas the cylinder body (13) is seen along the axial line (31c) of the cylinder (31), the outer contour (35) comprises a first depressed portion (71) that is located radially outward of the first hole (41) and that is depressed in a direction radially outward of the cylinder (31), the method comprising:preparing a mold (112) comprising a water jacket molding portion (112W) that has the same shape as the water jacket (12W) and that comprises a cooling passage (101) formed therein;injecting a metal material into the mold (112); andsupplying a coolant to flow through the cooling passage (101), thereby cooling the mold (112).
- The method for manufacturing an internal combustion engine (10) according to claim 1, wherein the first depressed portion (71) of the cylinder body (12) is formed next to the cooling passage (101) of the water jacket molding portion (112W).
- A method for manufacturing an internal combustion engine (10), wherein the internal combustion engine comprises:a cylinder body (12) comprising a cylinder (31), a water jacket (12W) formed around the cylinder (31), a first hole (41) that is formed outward of the water jacket (12W) in a radial direction of the cylinder (31) and that extends parallel to an axial line (31c) of the cylinder (31);a cylinder head (13) that comprises a hole extending on a center line (41c) of the first hole (41) and that covers the cylinder (31); anda first bolt (29) that is inserted into the first hole (41) and the hole of the cylinder head (13) to fasten together the cylinder head (13) and the cylinder body (12), wherein:as the cylinder body (12) is seen along the axial line (31c) of the cylinder (31), the cylinder body (12) comprises an outer contour (35) that defines an outer side of the water jacket (12W) in the radial direction of the cylinder (31), an inner contour (36) that defines an inner side of the water jacket (12W) in the radial direction of the cylinder (31), a first opposing surface (51) that is located outward of the outer contour (35) in the radial direction of the cylinder (31) and that opposes the cylinder head (13), and a second opposing surface (52) that is located inward of the inner contour (36) in the radial direction of the cylinder (31) and that opposes the cylinder head (13); andas the cylinder body (13) is seen along the axial line (31c) of the cylinder (31), the outer contour (35) comprises a first depressed portion (71) that is located radially outward of the first hole (41) and that is depressed in a direction radially outward of the cylinder (31), whereinthe cylinder body (12) comprises another cylinder (32) that extends parallel to the cylinder (31), and a third hole (43) that extends parallel to the axial line (31c) of the cylinder (31);the internal combustion engine (10) comprises a third bolt (29) that is inserted through the third hole (43) to fasten together the cylinder head (13) and the cylinder body (12);as the cylinder body (12) is seen along the axial line (31c) of the cylinder (31), a straight line (L11) passes through between the first hole (41) and the second hole (42), wherein the straight line (L11) passes through the center (31c) of the cylinder (31) and is perpendicular to a straight line (L3) that passes through the center (31c) of the cylinder (31) and a center (32c) of the other cylinder (32);as the cylinder body (12) is seen along the axial line (31c) of the cylinder (31), a straight line (L12) passes through between the second hole (42) and the third hole (43), wherein the straight line (L12) passes through the center (32c) of the other cylinder (32) and is perpendicular to the straight line (L3) that connects between the center (31c) of the cylinder (31) and the center (32c) of the other cylinder (32);the water jacket (12W) is formed around the cylinder (31) and the other cylinder (32); andas the cylinder body (12) is seen along the axial line (31c) of the cylinder (31), the outer contour (35) includes a third depressed portion (74) that is located radially outward of the third hole (43) and is depressed in a direction radially outward of the other cylinder (32), the method comprising:preparing a mold (112) comprising a water jacket molding portion (112W) that has the same shape as the water jacket (12W) and that comprises a first cooling passage (101) and a second cooling passage (102) formed therein;injecting a metal material into the mold (112); andsupplying a coolant to flow through the first cooling passage (101) and the second cooling passage (102), thereby cooling the mold (112), wherein:the first depressed portion (71) of the cylinder body (12) is formed next to the first cooling passage (101) of the water jacket molding portion (112W); anda connecting portion between the cylinder (31) and the other cylinder (32) is formed next to the second cooling passage (102) of the water jacket molding portion (112W).
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