CN103711560B

CN103711560B - Air-cooled internal combustion engine and the Straddle-type vehicle for possessing the air-cooled internal combustion engine

Info

Publication number: CN103711560B
Application number: CN201310460074.9A
Authority: CN
Inventors: 铃木贵晴; 橘内透
Original assignee: Yamaha Motor Co Ltd
Current assignee: Yamaha Motor Co Ltd
Priority date: 2012-10-01
Filing date: 2013-09-30
Publication date: 2017-09-22
Anticipated expiration: 2033-09-30
Also published as: CN103711560A; EP2713033A1; JP2014070621A; TW201418569A; TWI551774B; EP2713033B1

Abstract

The present invention relates to air-cooled internal combustion engine and possesses the Straddle-type vehicle of the air-cooled internal combustion engine.Air-cooled internal combustion engine possesses cylinder head body（100）, cylinder head body（100）Have：Multiple cold sinks（10）；To cam chamber（109）The cam locular wall being defined（20）；To combustion chamber（110）The chamber wall being defined（30）；For carrying out to combustion chamber（110）Air inlet intake channel（40）；For carrying out from combustion chamber（110）Exhaust exhaust channel（50）；For making cooling wind pass through cam locular wall（20）And chamber wall（30）Between cooling air passway（60）, cylinder head body（100）It is integrally formed by die-cast by aluminium alloy.Cylinder head body（100）Also have and house cam chain（113）Cam chain room（70）.From cylinder axis direction（D1）During observation, exhaust channel（50）With with from entrance side towards outlet side from cam chain room（70）Remote mode extends, and with exhaust channel（50）Axis（50x）Formed as linear mode.

Description

Air-cooled internal combustion engine and straddle-type vehicle provided with same

Technical Field

The present invention relates to internal combustion engines, and more particularly to air-cooled internal combustion engines. The present invention also relates to a straddle-type vehicle equipped with an air-cooled internal combustion engine.

Background

In recent years, there has been an increasing desire to operate an internal combustion engine at a higher compression ratio in order to improve fuel efficiency. However, when the compression ratio is increased, the temperature near the top dead center of the piston is likely to increase, and knocking is likely to occur.

In order to prevent such knocking, it is necessary to improve the cooling performance of the cylinder head. In general, in an air-cooled internal combustion engine, the cooling performance tends to be lower than in a water-cooled internal combustion engine, and therefore, in particular, in an air-cooled internal combustion engine, further improvement in the cooling performance of a cylinder head is required.

Therefore, it is considered to form the cylinder head by die casting, thereby thinning and providing a large number of cooling fins. Patent document 1 discloses a technique for molding a cylinder head having cooling fins by die casting. In the technique disclosed in patent document 1, when the cylinder head is formed by die casting, a previously prepared liner is cast in to form the intake passage and the exhaust passage. That is, the cylinder head includes separate members (a liner for forming the intake passage and a liner for forming the exhaust passage).

Prior art documents

Patent document 1: japanese patent application laid-open No. 2004-116464

Disclosure of Invention

However, the cylinder head disclosed in patent document 1 does not have a cooling air passage for receiving the cooling air to pass through. Therefore, even when the cylinder head of patent document 1 is used in an air-cooled internal combustion engine, sufficient cooling performance may not be obtained. Further, in die-casting, it is difficult to form an undercut shape (a shape in which it is difficult to remove a molded article by a normal mold opening when the molded article is taken out from a mold), and therefore, it is difficult to provide a cooling air passage having a sufficient cross-sectional area in a cylinder head molded by die-casting.

Further, in the case where the bush is cast as in patent document 1, the bush may be displaced and the intake passage and the exhaust passage may be displaced at the time of die casting, and as a result, the performance of the internal combustion engine may be degraded.

Therefore, it is preferable to form the intake passage and the exhaust passage without casting the bush in the die-casting, but a core is required for this purpose. However, in this case, the core may be misaligned, and thus the performance of the internal combustion engine may be degraded.

The present invention has been made in view of the above problems, and an object thereof is to provide an air-cooled internal combustion engine including a cylinder head body which is formed by die casting in a favorable manner, and which has a cooling air passage having a sufficient cross-sectional area.

An air-cooled internal combustion engine according to the present invention includes a cylinder head body having: a plurality of cooling fins; a cam chamber wall defining a cam chamber; a combustion chamber wall defining a combustion chamber; an intake passage for performing intake to the combustion chamber; an exhaust passage for performing exhaust from the combustion chamber; and a cooling air passage for passing cooling air between the cam chamber wall and the combustion chamber wall, wherein the cylinder head body is integrally formed of an aluminum alloy by die casting, the cylinder head body further includes a cam chain chamber for accommodating a cam chain, and the exhaust passage extends so as to be separated from the cam chain chamber as viewed from an inlet side toward an outlet side in a cylinder axial direction, and is formed so that an axis of the exhaust passage is linear.

In one embodiment, the plurality of cooling fins includes cooling fins extending from exhaust passage walls defining the exhaust passage.

In one embodiment, the inner peripheral surface of the exhaust passage has a surface roughness Rz of 30 μm or less.

In one embodiment, the cylinder head body further includes a plurality of bolt holes through which cylinder head bolts are inserted, 1 bolt hole of the plurality of bolt holes is provided between the exhaust passage and the cam chain chamber, and a part of the cooling air passage is located between the 1 bolt hole and the exhaust passage.

In one embodiment, the plurality of cooling fins are provided such that the total area of the cooling fins located on the combustion chamber side with respect to the top portion of the combustion chamber wall is larger than the total area of the cooling fins located on the opposite side of the combustion chamber with respect to the top portion of the combustion chamber wall.

In one embodiment, the plurality of cooling fins are provided such that, when viewed from the side opposite to the cam chain chamber with respect to the cylinder axis, an end portion on the cylinder axis side of the cooling fin located on the combustion chamber side with respect to the top portion of the combustion chamber wall is closer to the cylinder axis than an end portion on the cylinder axis side of the cooling fin located on the side opposite to the combustion chamber side with respect to the top portion of the combustion chamber wall.

In one embodiment, a part of the cooling wind passage is defined by an exhaust passage wall defining the exhaust passage, that is, an exhaust passage wall intersecting the cam chamber wall at an acute angle.

In one embodiment, the cam chamber wall has a thickness of 1.5mm or more and 2.5mm or less.

In one embodiment, the plurality of cooling fins have a thickness of 1.0mm to 2.5mm at their tip end portions, and are arranged at a pitch of 7.5mm or less.

In one embodiment, each of the plurality of cooling fins has a draft of 1.0 ° or more and 2.0 ° or less.

In one embodiment, the cylinder head body further has a rib provided in the cooling air passage and connecting the combustion chamber wall and the cam chamber wall.

In one embodiment, the ribs are formed along cooling wind passage walls defining the cooling wind passage.

In one embodiment, the roundness of the cross-sectional shape of the exhaust passage along a plane orthogonal to the axis of the exhaust passage is lower than the roundness of the shape of the outlet of the exhaust passage.

In one embodiment, a cross-sectional shape of the exhaust passage along a plane orthogonal to an axis of the exhaust passage is substantially elliptical, and a shape of an outlet of the exhaust passage is substantially perfect circle.

The straddle-type vehicle according to the present invention includes the air-cooled internal combustion engine having the above-described configuration.

In the air-cooled internal combustion engine according to the present invention, the exhaust passage of the cylinder head body extends so as to be spaced apart from the cam chain chamber as it goes from the inlet side to the outlet side, and therefore the space between the outlet of the exhaust passage and the cam chain chamber can be expanded. Therefore, it is easy to secure a sufficient cross-sectional area of the cooling air passage. Therefore, sufficiently high cooling performance can be achieved. In the internal combustion engine according to the present invention, the exhaust passage of the cylinder head body is formed such that the axis thereof is linear. Therefore, exhaust resistance can be reduced, and more efficient combustion can be performed. Further, when the cylinder head body is formed by die casting, the exhaust passage can be formed in the final shape by the mold, and therefore, it is not necessary to change the shape of the exhaust passage by subsequent processing.

Typically, the plurality of cooling fins includes cooling fins extending from an exhaust passage wall defining the exhaust passage. Since the exhaust passage is also a portion of the cylinder head body that is likely to reach a high temperature, the cooling fins extend from the exhaust passage wall, thereby improving the cooling efficiency.

When the shape of the exhaust passage is designed such that the axis thereof is linear, the exhaust passage can be easily formed by a mold without using a core. When the exhaust passage is formed by the mold, the surface roughness of the inner peripheral surface of the exhaust passage can be reduced as compared with the case where the core is used. More specifically, the surface roughness Rz (maximum height) of the inner peripheral surface of the exhaust passage can be set to 30 μm or less, and the exhaust resistance can be reduced to improve the output of the internal combustion engine. Further, by setting the surface roughness Rz of the inner peripheral surface of the intake passage to 30 μm or less, the intake resistance can be reduced and the output of the internal combustion engine can be further improved.

When the bolt hole through which the cylinder head bolt is inserted is provided between the exhaust passage and the cam chain chamber, it is necessary to locate (arrange) a part of the cooling air passage in a space narrower than the space between the exhaust passage and the cam chain chamber (that is, a space between the bolt hole and the exhaust passage). However, as described above, the exhaust passage extends so as to be separated from the cam chain chamber as it goes from the inlet side to the outlet side, and therefore, the cross-sectional area of the cooling air passage can be sufficiently secured even between the bolt hole and the exhaust passage.

The plurality of cooling fins are preferably provided such that the total area of the cooling fins located on the combustion chamber side with respect to the top portion of the combustion chamber wall is larger than the total area of the cooling fins located on the opposite side of the combustion chamber with respect to the top portion of the combustion chamber wall. During operation of the internal combustion engine, a region of the cylinder head body located on the combustion chamber side with respect to the top portion of the combustion chamber wall has a higher temperature than a region located on the opposite side of the combustion chamber with respect to the top portion of the combustion chamber wall. Therefore, the total area of the cooling fins located in the former region is made larger than the total area of the cooling fins located in the latter region, whereby the cooling performance can be effectively improved.

Preferably, the plurality of cooling fins are provided such that, when viewed from the side opposite to the cam chain chamber with respect to the cylinder axis, an end portion on the cylinder axis side of the cooling fin located on the combustion chamber side with respect to the top portion of the combustion chamber wall is closer to the cylinder axis than an end portion on the cylinder axis side of the cooling fin located on the opposite side of the combustion chamber with respect to the top portion of the combustion chamber wall. The cross-sectional area of the cooling air passage can be further increased by bringing the end portion on the cylinder axis side of the cooling fin located on the combustion chamber side with respect to the top portion of the combustion chamber wall closer to the cylinder axis than the end portion on the cylinder axis side of the cooling fin located on the opposite side of the combustion chamber with respect to the top portion of the combustion chamber wall, that is, by moving the end portion of the latter cooling fin farther from the cylinder axis than the end portion of the former cooling fin.

When a part of the cooling air passage is defined by an exhaust passage wall defining the exhaust passage, that is, an exhaust passage wall intersecting the cam chamber wall at an acute angle, the following advantages can be obtained. In general, when the shape of the cooling air passage is formed by a mold in die casting, a portion of the mold corresponding to the cooling air passage has a shape protruding from the other portion. The tip of the portion having such a protruding shape is likely to be at a high temperature due to the heat of the molten metal. Particularly, when the tip end has an angle, the angle is sometimes melted. Therefore, the tip is generally designed so that its cross section is circular. However, as in the present embodiment, the sectional area of the cooling air passage can be increased by defining a part of the cooling air passage by the exhaust passage wall that intersects the cam chamber wall at an acute angle. In this case, the wall thickness of both the cam chamber wall and the exhaust passage wall can be reduced, and therefore the problem of melting loss can be avoided.

The cam chamber wall preferably has a thickness of 2.5mm or less. By setting the thickness of the cam chamber wall to 2.5mm or less, the corner of the die can be more reliably prevented from being melted. However, when the thickness of the cam chamber wall is less than 1.5mm, the required compressive strength of the cam chamber cannot be sufficiently obtained, and the resistance to the deformation stress caused by the deformation may be insufficient, and therefore the thickness of the cam chamber wall is preferably 1.5mm or more.

In the air-cooled internal combustion engine according to the present invention, since the cylinder head body is formed by die casting, the thickness and pitch of the cooling fins can be reduced, and the cooling performance can be improved. Specifically, the thickness of the tip portion of each cooling fin can be set to 1.0mm or more and 2.5mm or less, and the plurality of cooling fins can be arranged at a pitch of 7.5mm or less, whereby the cooling performance can be improved.

Each of the plurality of cooling fins preferably has a draft of 2.0 ° or less. By reducing the draft to 2.0 ° or less, the interval between the root portions of the cooling fins can be increased, and thus the cooling performance can be further improved. However, from the viewpoint of easy mold release, the draft of each of the plurality of cooling fins is preferably 1.0 ° or more.

The cylinder head body preferably further includes a rib provided in the cooling air passage and connecting the combustion chamber wall and the cam chamber wall. The rib connects the combustion chamber wall and the cam chamber wall, and therefore, the rib transmits heat of the combustion chamber wall to the cam chamber wall, and the lubricating oil using the cam chamber can be cooled, and therefore, the cooling performance can be improved. Further, by disposing the ribs in the cooling air passage, the cooling effect by the cooling air can be obtained.

The ribs are preferably formed along a direction of drawing when the cylinder head body is formed by die-casting. Therefore, the rib is preferably formed along a wall portion (cooling wind passage wall) that defines the cooling wind passage.

Preferably, a cross-sectional shape of the exhaust passage along a plane orthogonal to an axis of the exhaust passage is substantially elliptical, and a shape of an outlet of the exhaust passage is substantially perfect circle. Since the cross-sectional shape of the exhaust pipe is generally a substantially perfect circle, by making the shape of the outlet of the exhaust passage substantially a perfect circle, it is possible to prevent a rapid change in the passage area and prevent a decrease in the performance of the internal combustion engine. When the exhaust passage extends so as to be spaced apart from the cam chain chamber as it goes from the inlet side toward the outlet side, if the sectional shape of the exhaust passage along the plane orthogonal to the axis is substantially perfect circle, the shape of the outlet of the exhaust passage cannot be substantially perfect circle. In contrast, the shape of the outlet of the exhaust passage can be made substantially perfect circle by making the sectional shape of the exhaust passage along the plane orthogonal to the axis substantially elliptical, that is, by making the roundness of the sectional shape of the exhaust passage along the plane orthogonal to the axis lower than the roundness of the shape of the outlet of the exhaust passage.

According to the present invention, it is possible to provide an air-cooled internal combustion engine provided with a cylinder head body having a cooling air passage and obtained by die casting with good formability, and the cooling air passage having a sufficient cross-sectional area.

Drawings

Fig. 1 is a right side view schematically showing a motorcycle (saddle-ride type vehicle) 1 in an embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line 2A-2A' of FIG. 1;

fig. 3 is an enlarged view of the vicinity of the engine (internal combustion engine) 101 shown in fig. 2;

fig. 4 is a right side view of a portion of the engine 101;

fig. 5 is a left side sectional view of the engine 101;

fig. 6 is a plan view schematically showing a cylinder head body 100 provided in an engine 101 according to an embodiment of the present invention;

fig. 7 is a bottom view schematically showing a cylinder head body 100 provided in an engine 101 according to an embodiment of the present invention;

fig. 8 is a front view schematically showing a cylinder head body 100 provided in an engine 101 according to an embodiment of the present invention;

fig. 9 is a back view schematically showing a cylinder head body 100 provided in an engine 101 according to an embodiment of the present invention;

fig. 10 is a left side view schematically showing a cylinder head body 100 provided in an engine 101 according to an embodiment of the present invention;

fig. 11 is a right side view schematically showing a cylinder head body 100 provided in an engine 101 according to an embodiment of the present invention;

fig. 12 is a view schematically showing a cylinder head body 100 provided in an engine 101 according to an embodiment of the present invention, and is a sectional view taken along line 12A-12A' in fig. 11;

fig. 13 is a view schematically showing a cylinder head body 100 provided in an engine 101 according to an embodiment of the present invention, and is a sectional view taken along line 13A-13A' in fig. 7;

fig. 14 is a schematic view showing a plurality of cooling fins 10 provided in the cylinder head body 100.

Description of the symbols:

1 Motor bicycle (straddle type vehicle)

10 Cooling fin

20 cam chamber wall

30 fuel chamber wall

32 spark plug hole

40 air intake passage

40a air inlet port

40b opening part

50 exhaust passage

50a exhaust port (inlet of exhaust passage)

50b opening (outlet of exhaust passage)

50x axis of exhaust passage

51 exhaust passage wall

60 cooling air passage

60a cooling air passage inlet

60b outlet of cooling air passage

70 cam chain chamber

80 cylinder head bolt boss

80a, 80b, 80c, 80d bolt holes

90 Ribs

100 cylinder head body

101 engines (internal combustion engine)

102 crankcase

103 cylinder block

104 cylinder cover

105 cylinder head cover

106 cylinders

108 camshaft

109 cam chamber

110 combustion chamber

113 cam chain

121 Cooling Fan

130 protective cover

141 intake pipe

142 exhaust pipe

161 air inlet valve

162 exhaust valve

CA cooling air

D1 cylinder axis direction

L1 Cylinder axis

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments.

Fig. 1 shows a straddle-type vehicle 1 according to the present embodiment. The saddle-ride type vehicle 1 shown in fig. 1 is a motorcycle of a scooter type. The saddle-ride type vehicle according to the present invention is not limited to the scooter type motorcycle 1. The saddle-ride type vehicle according to the present invention may be a motorcycle of another type such as a so-called moped type, off-road type, heavy-duty type, or the like. The saddle-ride type vehicle according to the present invention is not limited to a two-wheeled vehicle, and is an arbitrary vehicle in which a rider rides a vehicle. The straddle-type vehicle according to the present invention may be a three-wheel vehicle or the like of a type in which the traveling direction is changed by tilting the vehicle body, or may be another straddle-type vehicle such as an atv (all Terrain vehicle).

In the following description, front, rear, left, and right respectively represent front, rear, left, and right as viewed from a rider of the motorcycle 1. In the figure, reference symbols F, Re, L and R represent front, rear, left and right, respectively.

As shown in fig. 1, a motorcycle 1 includes a vehicle body 2, a front wheel 3, a rear wheel 4, and an engine unit 5 that drives the rear wheel 4. The vehicle body 2 includes a handle 6 operated by a passenger and a seat 7 on which the passenger sits. The engine unit 5 is a so-called unit swing type engine unit, and is supported by a vehicle body frame (not shown in fig. 1) so as to be able to swing about a pivot shaft 8. That is, the engine unit 5 is supported by the vehicle body frame so as to be able to swing.

Next, the structure of the engine unit 5 of the motorcycle 1 will be described more specifically with reference to fig. 2 to 5. Fig. 2 is a sectional view taken along line 2A-2A' in fig. 1. Fig. 3 is an enlarged view of the vicinity of engine 101 shown in fig. 2. Fig. 4 is a right side view of a part of the engine 101. Fig. 5 is a left side sectional view of the engine 101.

As shown in fig. 2, the engine unit 5 includes an engine (internal combustion engine) 101 and a V-belt type continuously variable transmission (hereinafter referred to as "CVT") 150. In the example shown in fig. 2, the engine 101 and the CVT150 are integrated to form the engine unit 5, but the engine 101 and the transmission may be provided separately.

The engine 101 is a single-cylinder engine having a single cylinder. The engine 101 is a 4-stroke engine in which an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke are sequentially repeated. The engine 101 includes: a crankcase 102; a cylinder block 103 extending forward from the crankcase 102 (the "forward" referred to herein is not limited to a direction that is strictly forward, i.e., parallel to the horizontal line, but also includes a direction inclined from the horizontal line) and coupled to the crankcase 102; a cylinder head 104 connected to a front portion of the cylinder block 103; a cylinder head cover 105 connected to the front of the cylinder head 104. A cylinder 106 is formed inside the cylinder block 103.

The cylinder 106 may be formed of a cylinder liner or the like inserted into the main body of the cylinder block 103 (i.e., a portion of the cylinder block 103 other than the cylinder 106), or may be integrated with the main body of the cylinder block 103. In other words, the cylinder 106 may be formed to be separable from the main body of the cylinder block 103, or may be formed to be inseparable from the main body of the cylinder block 103. A piston 107 is slidably accommodated in the cylinder 106. The piston 107 is configured to be freely reciprocated between the top dead center TDC and the bottom dead center BDC.

The cylinder head 104 is stacked on the cylinder block 103 in such a manner as to cover the cylinder 106. The cylinder head 104 includes a cylinder head body 100 made of an aluminum alloy, a valve train including a camshaft 108, an intake valve 161, an exhaust valve 162, and the like. The valve train is housed in the cam chamber 109. The portion 20 of the cylinder head body 100 that defines the cam chamber 20 is referred to as a cam chamber wall as described later.

A combustion chamber 110 is defined by the cylinder head body 100, the top surface of the piston 107, and the inner peripheral surface of the cylinder 106. The portion 30 of the body of the cylinder head 100 that defines the combustion chamber 110 is referred to as a combustion chamber wall as described below.

Piston 107 is coupled to crankshaft 112 via connecting rod 111. The crankshaft 112 extends leftward and rightward, and is supported by the crankcase 102. The camshaft 108 is driven by a cam chain 113 connected to a crankshaft 112. The cam chain 113 is accommodated in the cam chain chamber 70.

In the present embodiment, the crankcase 102, the cylinder block 103, the cylinder head 104, and the cylinder head cover 105 are separate bodies, but they are not necessarily separate bodies, and they may be integrated as appropriate. For example, the crankcase 102 may be formed integrally with the cylinder block 103, or the cylinder block 103 may be formed integrally with the cylinder head 104. Further, the cylinder head 104 may be formed integrally with the cylinder head cover 105.

As shown in fig. 2, the CVT150 includes: a first pulley 151 as a driving-side pulley; a second pulley 152 as a driven-side pulley; a V-belt 153 wound around the first pulley 151 and the second pulley 152. The left end of the crankshaft 112 protrudes leftward from the crankcase 102. The first pulley 151 is mounted on the left end portion of the crankshaft 112. The second pulley 152 is mounted to a main shaft 154. The main shaft 154 is coupled to a rear wheel shaft 155 via a gear mechanism not shown. A transmission case 156 is provided on the left side of the crankcase 102. The CVT150 is housed in a transmission case 156.

A generator 120 is provided at the right side portion of the crankshaft 112. A cooling fan 121 is fixed to a right end of the crankshaft 112. The cooling fan 121 rotates together with the crankshaft 112. The cooling fan 121 is formed to rotate to suck air leftward. A shroud 130 is provided to the crankcase 102, the cylinder block 103, and the cylinder head 104. The generator 120 and the cooling fan 121 are housed in the shroud 130.

As shown in fig. 4, the engine 101 is a type in which a cylinder block 103 and a cylinder head 104 extend in a horizontal direction or in a direction inclined slightly forward and upward from the horizontal direction, that is, a so-called transverse engine. Reference symbol L1 in the figure denotes a line (cylinder axis) passing through the center of the cylinder 106. The cylinder axis L1 extends in the horizontal direction or in a direction slightly inclined from the horizontal direction. However, the direction of the cylinder axis L1 is not particularly limited. For example, the inclination angle of the cylinder axis L1 with respect to the horizontal plane may be 0 ° to 15 °, or may be larger. In the figure, reference symbol L2 denotes a center line of the crankshaft 112.

An intake pipe 141 is connected to an upper portion of the cylinder head 104. An exhaust pipe 142 is connected to a lower portion of the cylinder head 104. An intake passage 40 and an exhaust passage 50 are formed inside the cylinder head 104. The intake pipe 141 is connected to the intake passage 40, and the exhaust pipe 142 is connected to the exhaust passage 50. An intake valve 161 and an exhaust valve 162 are provided in the intake passage 40 and the exhaust passage 50, respectively.

The engine 101 of the present embodiment is an air-cooled engine cooled by air. As shown in fig. 2 to 4, a plurality of cooling fins 114 are formed in the cylinder block 103. The cooling fins 114 extend in a direction substantially orthogonal to the cylinder axis L1. As will be described later, a plurality of cooling fins 10 are also formed in the cylinder head body 100 (see fig. 8 to 10).

The shroud 130 includes an inner member 131 and an outer member 132, and is formed by assembling the inner member 131 and the outer member 132. As shown in fig. 4, the inner member 131 and the outer member 132 are fixed by bolts 133. The inner member 131 and the outer member 132 are formed of, for example, synthetic resin.

The inner member 131 is formed with a hole 131a into which the ignition device 115 such as an ignition plug is inserted. The outer member 132 has a suction port 132 a. When the shroud 130 is attached to the engine unit 5, the suction port 132a is disposed at a position facing the cooling fan 121 (see fig. 3). In fig. 4, reference symbol F denotes the outer circumference of the cooling fan 121, and reference symbol B denotes the rotational direction of the cooling fan 121.

The shroud 130 is attached to the crankcase 102, the cylinder block 103, and the cylinder head 104, and extends forward along the cylinder block 103 and the cylinder head 104. The shroud 130 covers the crankcase 102, the cylinder block 103, and the right side portion of the cylinder head 104. A part of the shroud 130 also covers the cylinder block 103 and a part of the upper and lower portions of the cylinder head 104.

When the cooling fan 121 rotates with the rotation of the crankshaft 112, air outside the shroud 30 is introduced into the shroud 30 through the intake port 132 a. The air introduced into the shroud 30 is blown onto the cylinder block 103 and the cylinder head 104. The cylinder block 103 and the cylinder head 104 are cooled by this air.

Next, the structure of the cylinder head body 100 provided in the engine 101 according to the present embodiment will be specifically described with reference to fig. 6 to 13. Fig. 6 and 7 are a plan view and a bottom view schematically showing the cylinder head body 100. Fig. 8 and 9 are front and rear views schematically showing the cylinder head body 100. Fig. 10 and 11 are left and right side views schematically showing the cylinder head body 100. Also, fig. 12 is a sectional view taken along line 12A-12A 'in fig. 11, and fig. 13 is a sectional view taken along line 8A-8A' in fig. 7. In some of the drawings, the cylinder axis direction is represented by arrow D1. It should be noted that the cylinder axis direction is a direction parallel to the cylinder axis L1, as a matter of course. In the following, the side to be connected to the intake pipe 141 is explained as the front side of the cylinder head body 100.

As shown in fig. 6 to 13, the cylinder head body 100 includes a plurality of cooling fins 10, a cam chamber wall 20, and a combustion chamber wall 30. The cylinder head body 100 further includes an intake passage 40, an exhaust passage 50, and a cooling air passage 60.

As shown in fig. 8, 9, and 10, the plurality of cooling fins 10 are provided on the outer side surface (more specifically, the left side surface) of the cylinder head body 100 and formed so as to protrude outward of the cylinder head body 100 (that is, so as to extend in a direction substantially orthogonal to the cylinder axis direction D1). The plurality of cooling fins 10 are arranged at a predetermined pitch along the cylinder axis direction D1. The number of cooling fins 10 is not limited to the example shown here.

The cam chamber wall 20 (shown in fig. 6, 10 and 13) defines a cam chamber 109. The cam chamber 109 houses a valve mechanism including the camshaft 108. A space between the cylinder head cover 105 attached to the upper portion of the cylinder head body 100 and the cam chamber wall 20 is a cam chamber 109.

The combustion chamber walls 30 (shown in fig. 7, 10 and 13) define a combustion chamber 110. Combustion chamber 110 is a space formed by combustion chamber wall 30 of cylinder head body 100, the top surface of piston 107, and the inner peripheral surface of cylinder 106. As shown in fig. 7, a spark plug hole 32 is formed in the combustion chamber wall 30 in addition to an intake port 40a and an exhaust port 50a, which will be described later. An ignition plug of the ignition device 115 is mounted on the plug hole 32.

The intake passage 40 is a passage for performing intake to the combustion chamber 110. An opening 40a of the intake passage 40 on the combustion chamber wall 30 side serves as an intake port. The intake valve 161 is moved up and down by the valve mechanism to open and close the intake port 40 a. An intake pipe 141 is connected to an opening 40b (located on the front surface of the cylinder head body 100) of the intake passage 40 on the side opposite to the combustion chamber wall 30.

The exhaust passage 50 is a passage for exhausting gas from the combustion chamber 110. An opening 50a of the exhaust passage 50 on the combustion chamber wall 30 side serves as an exhaust port. The exhaust valve 162 is moved up and down by the valve mechanism, thereby opening and closing the exhaust port 50 a. An exhaust pipe 142 is connected to an opening 50b of the exhaust passage 50 on the side opposite to the combustion chamber wall 30.

Typically, the plurality of cooling fins 10 includes cooling fins 10 extending from the exhaust passage walls defining the exhaust passage 50 (located relatively on the right side in fig. 10). In the present embodiment, the plurality of cooling fins 10 further includes cooling fins 10 extending from the intake passage wall defining the intake passage 40 (relatively on the left side in fig. 10).

The cooling air passage 60 (shown in fig. 10 and 13) is a passage for passing cooling air between the cam chamber wall 20 and the combustion chamber wall 30. As shown in fig. 7, the inlet 60a of the cooling air passage 60 is located on the left side surface of the cylinder head body 100, and the outlet 60b of the cooling air passage 60 is located on the right side surface of the cylinder head body 100. The cooling air CA introduced into the shroud 130 by the cooling fan 121 is introduced into the cooling air passage 60 from the inlet 60a, cools the cylinder head body 100 while passing through the cooling air passage 60, and is then discharged to the outside of the cylinder head body 100 from the outlet 60 b.

The cylinder head body 100 is integrally formed of an aluminum alloy by die casting. As the aluminum alloy, for example, ADC10 or ADC12 is preferably used.

As shown in fig. 6, 7, and 12, the cylinder head body 100 further includes a cam chain chamber 70 that accommodates a cam chain 113. The cam chain 113 is a member for driving the camshaft 108 of the valve train.

The exhaust passage 50 extends so as to be distant from the cam chain chamber 70 from the inlet (exhaust port 50 a) side toward the outlet (opening 50 b) side when viewed from the cylinder axial direction D1 (the direction perpendicular to the paper surface in fig. 6, 7, and 12). That is, the axis 50x of the exhaust passage 50 is inclined with respect to the front-rear direction of the cylinder head body 100. The axis 50x of the exhaust passage 50 is formed linearly when viewed from the cylinder axis direction D1.

As shown in fig. 6, 7, and 12, the cylinder head body 100 has a plurality of bolt holes 80a to 80d for receiving cylinder head bolts. The cylinder head body 100 is coupled to the cylinder block 103 by a head bolt (typically, a stud bolt) inserted through the bolt holes 80a to 80 d. 1 bolt hole (a bolt hole located at the upper right in fig. 6 and 12 and at the lower right in fig. 7) 80a of the plurality of (4 in this case) bolt holes 80a to 80d is provided between the exhaust passage 50 and the cam chain chamber 70. A part of the cooling air passage 60 is located between the bolt hole 80a and the exhaust passage 50. The bosses 80 having the bolt holes 80a to 80d are also referred to as bosses for cylinder head bolts or bosses for stud bolts.

As described above, the cylinder head body 100 of the engine (internal combustion engine) 101 in the embodiment of the present invention is integrally formed by die casting. That is, unlike the cylinder head of patent document 1, a separate member, i.e., a bush, is not cast into the cylinder head body 100. Therefore, the misalignment of the intake passage 40 and the exhaust passage 50 due to the misalignment of the bush does not occur, and the performance of the engine 101 is prevented from being degraded due to the misalignment of the intake passage 40 or the exhaust passage 50.

Further, since the exhaust passage 50 extends so as to be distant from the cam chain chamber 70 as going from the inlet side toward the outlet side, the space between the outlet of the exhaust passage 50 and the cam chain chamber 70 can be expanded. Therefore, it is easy to secure a sufficiently large cross-sectional area of the cooling air passage 60. Therefore, sufficiently high cooling performance can be achieved.

The exhaust passage 50 is formed such that the axis 50x thereof is linear. Therefore, exhaust resistance can be reduced, and more efficient combustion can be performed. Further, when the cylinder head body 100 is formed by die casting, the exhaust passage 50 having the final shape can be formed by a mold, and therefore, it is not necessary to change the shape of the exhaust passage 50 by subsequent processing.

From the viewpoint of securing a sufficiently large cross-sectional area of the cooling air passage 60, the axis 50x of the exhaust passage 50 is preferably inclined at a large angle of a certain degree or more with respect to the front-rear direction. Specifically, the axis 50x of the exhaust passage 50 is preferably inclined at an angle of 20 ° or more with respect to the straight line L3 when viewed from the cylinder axial direction D1, and the straight line L3 is a straight line connecting the centers of 2 bolt holes 80a and 80b located on the cam chain chamber 70 side among the 4 bolt holes 80a to 80D. However, if the inclination angle is too large, the exhaust resistance becomes too large, and therefore the inclination angle is preferably 30 ° or less.

When one bolt hole 80a of the plurality of bolt holes 80a to 80d is provided between the exhaust passage 50 and the cam chain chamber 70 as in the present embodiment, it is necessary to locate (arrange) a part of the cooling air passage 60 in a space narrower than the space between the exhaust passage 50 and the cam chain chamber 70 (i.e., a space between the bolt hole 80a and the exhaust passage 50). However, as described above, the exhaust passage 50 extends so as to be distant from the cam chain chamber 70 from the inlet side toward the outlet side, and therefore, the cross-sectional area of the cooling air passage 60 can be sufficiently secured between the bolt hole 80a and the exhaust passage 50.

Further, when the shape of the exhaust passage 50 is designed such that the axis 50x thereof is straight, the exhaust passage 50 can be easily formed by a mold without using a core. When the exhaust passage 50 is formed by a mold, the surface roughness of the inner peripheral surface of the exhaust passage 50 can be reduced as compared with the case where a core is used. More specifically, the surface roughness Rz (maximum height) of the inner peripheral surface of the exhaust passage 50 can be set to 30 μm or less, and the exhaust resistance can be reduced to improve the output of the engine 101. By setting the surface roughness Rz of the inner peripheral surface of the intake passage 40 to 30 μm or less, the intake resistance can be reduced, and the output of the engine 101 can be further improved.

The plurality of cooling fins 10 preferably includes cooling fins 10 extending from the exhaust passage walls defining the exhaust passage 50. Since the exhaust passage 50 is also a portion that is likely to reach a high temperature in the cylinder head body 100, the cooling fins 10 extend from the exhaust passage wall, thereby improving the cooling efficiency. From the viewpoint of ensuring sufficiently high cooling efficiency, more specifically, the cooling fins 10 extending from the exhaust passage wall extend from at least a portion of the exhaust passage wall that is located closer to the cylinder axis L1 than the bosses (bosses for stud bolts) 80 corresponding to the bolt holes (bolt holes closest to the cooling fins 10 extending from the exhaust passage wall) 80c (see fig. 10).

Among the plurality of cooling fins 10, the cooling fin 10a located on the combustion chamber 110 side with respect to the top portion of the combustion chamber wall 30 is referred to as a "first cooling fin", and the cooling fin 10b located on the opposite side (i.e., cam chamber side) of the combustion chamber 110 with respect to the top portion of the combustion chamber wall 30 is referred to as a "second cooling fin". In the present embodiment, as is apparent from fig. 8, 9, and 10, the plurality of cooling fins 10 are provided such that the total area of the first cooling fins 10a is larger than the total area of the second cooling fins 10 b.

During operation of engine 101, a region of cylinder head body 100 on the side of combustion chamber 110 with respect to the top portion of combustion chamber wall 30 has a higher temperature than a region on the opposite side of combustion chamber 110 with respect to the top portion of combustion chamber wall 30. Therefore, the total area of the first cooling fins 10a located in the former region is made larger than the total area of the second cooling fins 10b located in the latter region, whereby the cooling performance can be effectively improved.

In the present embodiment, as shown in fig. 10, the plurality of cooling fins 10 are arranged such that, when viewed from the side opposite to the cam chain chamber 70 with respect to the cylinder axis L1 (when viewed from the direction perpendicular to the paper surface in fig. 10), the end portion 10a1 of the first cooling fin 10a on the cylinder axis L1 side is located closer to the cylinder axis L1 than the end portion 10b1 of the second cooling fin 10b on the cylinder axis L1 side. That is, the end 10b1 of the second cooling fin 10b is farther from the cylinder axis L1 than the end 10a1 of the first cooling fin 10 a. This can further increase the cross-sectional area of the cooling air passage 60.

In the present embodiment, as shown in fig. 10, a part of the cooling air passage 60 is defined by an exhaust passage wall 51 defining the exhaust passage 50, that is, an exhaust passage wall 51 intersecting the cam chamber wall 20 at an acute angle. This provides the following advantages.

In general, when the shape of the cooling air passage is formed by a mold in die casting, a portion of the mold corresponding to the cooling air passage has a shape protruding from the other portion. The tip of the portion having such a protruding shape is likely to be at a high temperature due to the heat of the molten metal. Particularly, when the tip end has an angle, the angle is sometimes melted. Therefore, the tip is generally designed so that its cross section is circular. However, as in the present embodiment, the sectional area of the cooling air passage 60 can be increased by defining a part of the cooling air passage 60 by the exhaust passage wall 51 intersecting the cam chamber wall 20 at an acute angle. In this case, the wall thickness of both the cam box wall 20 and the exhaust passage wall 51 can be reduced, and therefore the problem of melting loss can be avoided.

The cam chamber wall 20 preferably has a thickness of 2.5mm or less. By setting the thickness of the cam box wall 20 to 2.5mm or less, the corner of the die can be more reliably prevented from being melted. However, when the thickness of the cam chamber wall 20 is less than 1.5mm, the required compressive strength of the cam chamber 109 cannot be sufficiently obtained, and the resistance to the deformation stress due to the deformation may be insufficient, and therefore the thickness of the cam chamber wall 20 is preferably 1.5mm or more.

In addition, in the present embodiment, since the cylinder head body 100 is formed by die casting, the thickness and pitch of the cooling fins 10 can be reduced, and the cooling performance can be improved. Specifically, as shown in fig. 14, when the thickness t of the tip portion of each of the plurality of cooling fins 10 is t and the pitch p of the plurality of cooling fins 10 is p, the thickness t of the tip portion of each of the plurality of cooling fins 10 may be 1.0mm or more and 2.5mm or less, and the plurality of cooling fins 10 may be arranged at the pitch p of 7.5mm or less.

Each of the plurality of cooling fins 10 preferably has a draft of 2.0 ° or less. By reducing the draft to 2.0 ° or less, the interval between the root portions of the cooling fins 10 can be increased, and thus the cooling performance can be further improved. However, from the viewpoint of easy mold release, the draft of each of the plurality of cooling fins 10 is preferably 1.0 ° or more.

As shown in fig. 10, the cylinder head body 100 of the present embodiment further includes a rib 90 provided in the cooling air passage 60 and connecting the combustion chamber wall 30 and the cam chamber wall 20. The rib 90 connects the combustion chamber wall 30 and the cam chamber wall 20, and therefore the rib 90 transmits the heat of the combustion chamber wall 30 to the cam chamber wall 20, and the lubricating oil using the cam chamber 109 can be cooled, and therefore, the cooling performance can be improved. Further, by disposing the ribs 90 in the cooling air passage 60, the cooling effect by the cooling air CA can be obtained.

The rib 90 is preferably formed along a drawing direction in forming the cylinder head body 100 by die-casting. Therefore, the ribs 90 are preferably formed along wall portions (cooling wind passage walls) that define the cooling wind passage 60.

Further, it is preferable that the cross-sectional shape of the exhaust passage 50 along a plane orthogonal to the axis 50x of the exhaust passage 50 is substantially elliptical, and the shape of the outlet 50b of the exhaust passage 50 is substantially perfect circle as shown in fig. 9. Since the cross-sectional shape of the exhaust pipe 142 is generally a substantially perfect circle, the outlet 50b of the exhaust passage 50 is formed into a substantially perfect circle, thereby preventing a rapid change in the passage area and preventing a decrease in the performance of the engine 101. As described above, since the exhaust passage 50 extends so as to be distant from the cam chain chamber 70 as it goes from the inlet side toward the outlet side, when the sectional shape of the exhaust passage 50 along the plane orthogonal to the axis 50x is a substantially perfect circle, the shape of the outlet 50b of the exhaust passage 50 cannot be made a substantially perfect circle. By making the cross-sectional shape of the exhaust passage 50 along the plane orthogonal to the axis 50x substantially elliptical, that is, by making the roundness of the cross-sectional shape of the exhaust passage 50 along the plane orthogonal to the axis 50x lower than the roundness of the shape of the outlet 50b of the exhaust passage 50, the shape of the outlet 50b of the exhaust passage 50 can be made substantially perfect circle.

Further, the wall defining the cooling air passage 60 or the cam chain chamber 109 and the outer surface including the plurality of cooling fins 10 are preferably subjected to shot peening. The roughened surface formed by the shot peening treatment can increase the area in contact with the cooling air CA, and therefore, the cooling performance can be further improved. Further, the burr removal of the cooling air passage 60 can be performed by the shot blasting.

In order to further improve the cooling performance, it is also preferable to provide cooling fins extending from the rib 90 or to subject the rib 90 to shot peening.

The internal combustion engine 1000 according to the embodiment of the present invention is suitably applicable to various straddle-type vehicles such as a motorcycle and an atv (all terrainvehicle). Moreover, the present invention can be suitably applied to a generator and the like.

Industrial applicability of the invention

According to the present invention, it is possible to provide an air-cooled internal combustion engine provided with a cylinder head body having a cooling air passage and obtained by die casting with good formability, and the cooling air passage having a sufficient cross-sectional area. The air-cooled internal combustion engine of the present invention is excellent in cooling performance of the cylinder head body, and therefore can be suitably applied to various saddle-type vehicles including a motorcycle.

Claims

1. An air-cooled internal combustion engine is provided with a cylinder head body, and the cylinder head body is provided with: a plurality of cooling fins;

a cam chamber wall defining a cam chamber;

a combustion chamber wall defining a combustion chamber;

an intake passage for performing intake to the combustion chamber;

an exhaust passage for performing exhaust from the combustion chamber; and

a cooling air passage for passing cooling air between the cam chamber wall and the combustion chamber wall;

wherein,

the cylinder head body is integrally formed of an aluminum alloy by die casting,

the cylinder head body also has a cam chain chamber housing a cam chain,

the exhaust passage extends so as to be separated from the cam chain chamber as seen from the cylinder axial direction from the inlet side toward the outlet side, and is formed so that the axis of the exhaust passage is linear,

the roundness of the cross-sectional shape of the exhaust passage along a plane orthogonal to the axis of the exhaust passage is lower than the roundness of the shape of the outlet of the exhaust passage,

the cross-sectional shape of the exhaust passage along a plane orthogonal to the axis of the exhaust passage is substantially elliptical, and the shape of the outlet of the exhaust passage is substantially perfect circle.

2. The air-cooled internal combustion engine according to claim 1,

the plurality of cooling fins includes cooling fins extending from exhaust passage walls defining the exhaust passage.

3. The air-cooled internal combustion engine according to claim 1 or 2, wherein,

the inner peripheral surface of the exhaust passage has a surface roughness Rz of 30 [ mu ] m or less.

4. The air-cooled internal combustion engine according to claim 1,

the cylinder head body further has a plurality of bolt holes through which the cylinder head bolts are inserted,

one of the plurality of bolt holes is provided between the exhaust passage and the cam chain chamber,

a portion of the cooling wind passage is located between the one bolt hole and the exhaust passage.

5. The air-cooled internal combustion engine according to claim 1,

the plurality of cooling fins are configured to: the total area of the cooling fins on the combustion chamber side with respect to the top of the combustion chamber wall is made larger than the total area of the cooling fins on the opposite side of the combustion chamber with respect to the top of the combustion chamber wall.

6. The air-cooled internal combustion engine according to claim 1,

the plurality of cooling fins are arranged to: when viewed from the side opposite to the cam chain chamber with respect to the cylinder axis, an end portion of the cooling fin on the cylinder axis side of the combustion chamber side with respect to the top portion of the combustion chamber wall is closer to the cylinder axis than an end portion of the cooling fin on the cylinder axis side of the combustion chamber side with respect to the top portion of the combustion chamber wall.

7. The air-cooled internal combustion engine according to claim 1,

a part of the cooling wind passage is defined by an exhaust passage wall defining the exhaust passage, that is, an exhaust passage wall intersecting the cam chamber wall at an acute angle.

8. The air-cooled internal combustion engine according to claim 7,

the cam chamber wall has a thickness of 1.5mm or more and 2.5mm or less.

9. The air-cooled internal combustion engine according to claim 1,

the front end portions of the plurality of cooling fins have a thickness of 1.0mm to 2.5mm,

the plurality of cooling fins are arranged at a pitch of 7.5mm or less.

10. The air-cooled internal combustion engine according to claim 1,

the plurality of cooling fins each have a draft of 1.0 ° or more and 2.0 ° or less.

11. The air-cooled internal combustion engine according to claim 1,

the cylinder head body further includes a rib provided in the cooling air passage and connecting the combustion chamber wall and the cam chamber wall.

12. The air-cooled internal combustion engine according to claim 11,

the rib is formed along a cooling wind passage wall defining the cooling wind passage.

13. A straddle-type vehicle provided with the air-cooled internal combustion engine according to any one of claims 1 to 12.