Air-cooling type internal combustion engine and saddled vehicle having the same

Abstract

 There is provided an air-cooling type internal combustion engine including a cylinder head body which has a cooling air duct with a sufficient cross-sectional area and which can be suitably molded by die casting.
An air-cooling type internal combustion engine according to the present invention includes a cylinder head body 100, the cylinder head body 100 including: a plurality of cooling fins 10; a cam chamber wall 20 defining a cam chamber 109; a combustion chamber wall 30 defining a combustion chamber 110; an intake duct 40 through which air intake into the combustion chamber 110 is to occur; an exhaust duct 50 through which exhaust from the combustion chamber 110 is to occur; and a cooling air duct 60 for allowing cooling air o pass through the cam chamber wall 20 and the combustion chamber wall 30. The cylinder head body 100 is integrally molded from an aluminum alloy by die casting. The cylinder head body 100 further includes a cam chain chamber 70 for accommodating a cam chain 113. When viewed in the cylinder axis direction D1, the exhaust duct 50 extends in such a manner that the exhaust duct 50 becomes more distant from the cam chain chamber 70 when going from the inlet side toward the outlet side, and the exhaust duct 50 is formed so that an axis 50x of the exhaust duct 50 is linear.

Description

BACKGROUND

1. Technical Field:

[0001] The present invention relates to an internal combustion engine, and more particularly to an air-cooling type internal combustion engine. Moreover, the present invention relates to a saddled vehicle having an air-cooling type internal combustion engine.

2. Description of the Related Art:

[0002] In recent years, for improved mileage, there is a desire to operate internal combustion engines at higher compression ratios. However, increasing the compression ratio is likely to allow the temperature near the top dead center of the piston to increase, thus inducing knocking.

[0003] In order to prevent such knocking, it is necessary to enhance the coolability of the cylinder head. Generally speaking, an air-cooling type internal combustion engine tends to have poorer coolability than that of a water-cooling type internal combustion engine. Thus, it may be said that a further enhancement in the coolability of the cylinder head is especially desired in air-cooling type internal combustion engines.

[0004] Therefore, it might be conceivable to provide a large number of thin cooling fins through molding the cylinder head by die casting. Japanese Laid-Open Patent Publication No. 2004-116464 (hereinafter, "Patent Document 1") discloses molding a cylinder head with cooling fins by die casting. Moreover, in the technique disclosed in Patent Document 1, when molding a cylinder head by die casting, previously-prepared liners are cast together to form an intake duct and an exhaust duct. In other words, the cylinder head contains separate members (i.e., a liner for intake duct formation and a liner for exhaust duct formation).

[0005] However, in the cylinder head disclosed in Patent Document 1, no cooling air duct is formed for allowing cooling air to come through. Therefore, even if the cylinder head of Patent Document 1 is used in an air-cooling type internal combustion engine, it is possible that sufficient coolability may not be obtained. Moreover, the difficulty to form an undercut shape (which is a shape that hinders release through a usual mold-opening maneuver when the molding is to be taken out of the die) by die casting makes it difficult to provide a cooling air duct having a sufficient cross-sectional area on a cylinder head which is molded by die casting.

[0006] Furthermore, in the case where liners are cast together as in Patent Document 1, misalignments of the liners may occur at die casting, thus causing misalignments of the intake duct and the exhaust duct, whereby the performance of the internal combustion engine may be deteriorated.

[0007] Therefore, it is preferable to form the intake duct and the exhaust duct without casting liners together during die casting, which would mean that cores must be used. In that case, however, misalignments of the cores may occur, which in itself may deteriorate the performance of the internal combustion engine.

SUMMARY

[0008] The present invention has been made in view of the above problems, and an objective thereof is to provide an air-cooling type internal combustion engine including a cylinder head body which has a cooling air duct with a sufficient cross-sectional area and which can be suitably molded by die casting.

[0009] An air-cooling type internal combustion engine according to the present invention comprises a cylinder head body, the cylinder head body including: a plurality of cooling fins; a cam chamber wall defining a cam chamber; a combustion chamber wall defining a combustion chamber; an intake duct through which air intake into the combustion chamber is to occur; an exhaust duct through which exhaust from the combustion chamber is to occur; and a cooling air duct for allowing cooling air to pass through between the cam chamber wall and the combustion chamber wall, wherein, the cylinder head body is integrally molded from an aluminum alloy by die casting; the cylinder head body further includes a cam chain chamber for accommodating a cam chain; and when viewed in a cylinder axis direction, the exhaust duct extends in such a manner that the exhaust duct becomes more distant from the cam chain chamber when going from an inlet side toward an outlet side and the exhaust duct is formed so that an axis of the exhaust duct is linear.

[0010] In one embodiment, the plurality of cooling fins include a cooling fin extending from an exhaust duct wall defining the exhaust duct.

[0011] In one embodiment, an inner peripheral surface of the exhaust duct has a surface roughness Rz of 30 µm or less.

[0012] In one embodiment, the cylinder head body further includes a plurality of bolt holes, into each of which a head bolt is to be inserted; one of the plurality of bolt holes is provided between the exhaust duct and the cam chain chamber; and a portion of the cooling air duct is located between the one bolt hole and the exhaust duct.

[0013] In one embodiment, the plurality of cooling fins are provided in such a manner that a total area of those cooling fins which are located on the combustion chamber side of an apex of the combustion chamber wall is greater than a total area of those cooling fins which are located on an opposite side of the combustion chamber from the apex of the combustion chamber wall.

[0014] In one embodiment, the plurality of cooling fins are provided so that, when viewed from an opposite side of the cylinder axis from the cam chain chamber, cylinder-axis-side edges of those cooling fins which are located on the combustion chamber side of the apex of the combustion chamber wall are closer to the cylinder axis than are cylinder-axis-side edges of those cooling fins which are located on an opposite side of the apex of the combustion chamber wall from the combustion chamber.

[0015] In one embodiment, a portion of the cooling air duct is defined by an exhaust duct wall defining the exhaust duct, the exhaust duct wall intersecting the cam chamber wall at an acute angle.

[0016] In one embodiment, the cam chamber wall has a thickness of not less than 1.5 mm and not more than 2.5 mm.

[0017] In one embodiment, a leading edge of each of the plurality of cooling fins has a thickness of not less than 1.0 mm and not more than 2.5 mm; and the plurality of cooling fins are disposed with a pitch of 7.5 mm or less.

[0018] In one embodiment, each of the plurality of cooling fins has a draft of not less than 1.0° and not more than 2.0°.

[0019] In one embodiment, the cylinder head body further includes a rib which is provided within the cooling air duct, the rib linking together the combustion chamber wall and the cam chamber wall.

[0020] In one embodiment, the rib is formed along a cooling air duct wall defining the cooling air duct.

[0021] In one embodiment, a circularity of a cross-sectional shape of the exhaust duct along a plane which is orthogonal to the axis of the exhaust duct is lower than a circularity of the shape of an outlet of the exhaust duct.

[0022] In one embodiment, the cross-sectional shape of the exhaust duct along the plane which is orthogonal to the axis of the exhaust duct is a substantial ellipse, and the shape of the outlet of the exhaust duct is a substantially perfect circle.

[0023] A saddled vehicle according to the present invention comprises an air-cooling type internal combustion engine of the above construction.

[0024] In the air-cooling type internal combustion engine according to the present invention, the exhaust duct of the cylinder head body extends in such a manner that the exhaust duct becomes more distant from the cam chain chamber when going from the inlet side toward the outlet side, whereby the space between the outlet of the exhaust duct and the cam chain chamber can be expanded. Therefore, it is easy to secure a sufficiently large cross-sectional area of the cooling air duct. This realizes a sufficiently high coolability. Moreover, in the internal combustion engine according to the present invention, the exhaust duct of the cylinder head body is formed so that its axis is linear. Therefore, exhaust resistance can be reduced, and a more efficient combustion is enabled. Furthermore, when molding the cylinder head body by die casting, the exhaust duct in its final shape can be formed with a die, which makes it unnecessary to employ subsequent machining to change the shape of the exhaust duct.

[0025] Typically, the plurality of cooling fins include those cooling fins which extend from the exhaust duct wall defining the exhaust duct. Since the exhaust duct is one place in the cylinder head body that is liable to high temperature, the cooling fins extending from the exhaust duct wall will allow for an improved cooling efficiency.

[0026] When the shape of the exhaust duct is designed so that its axis is linear, it is easy to form the exhaust duct by using a die, without using any cores. By forming the exhaust duct with a die, it is possible to make the surface roughness of the inner peripheral surface of the exhaust duct smaller than that when cores are used. More specifically, the surface roughness Rz (maximum height) of the inner peripheral surface of the exhaust duct can be made 30 µm or less, thus reducing exhaust resistance and improving the output power of the internal combustion engine. Furthermore, by also ensuring that the surface roughness Rz of the inner peripheral surface of the intake duct is 30 µm or less, intake resistance can be reduced to further improve the output power of the internal combustion engine.

[0027] When a bolt hole in which a head bolt is to be inserted is provided between the exhaust duct and the cam chain chamber, it is necessary that a portion of the cooling air duct be located (disposed) in a space which is narrower than that between the exhaust duct and the cam chain chamber (i.e., a space between the bolt hole and the exhaust duct). However, as described above, the exhaust duct extends in such a manner that the exhaust duct becomes more distant from the cam chain chamber when going from the inlet side toward the outlet side; therefore, a sufficiently large cross-sectional area of the cooling air duct can be ensured also between the bolt hole and the exhaust duct.

[0028] Preferably, the plurality of cooling fins are provided in such a manner that a total area of those cooling fins which are located on the combustion chamber side of an apex of the combustion chamber wall is greater than a total area of those cooling fins which are located on the opposite side of the apex of the combustion chamber wall from the combustion chamber. During the operation of the internal combustion engine, within the cylinder head body, the region which is on the combustion chamber side of the apex of the combustion chamber wall has a higher temperature than the region on the opposite side of the apex of the combustion chamber wall from the combustion chamber. Therefore, coolability can be efficiently improved by ensuring that a total area of the cooling fins located in the former region is greater than a total area of the cooling fins located in the latter region.

[0029] Moreover, it is preferable that the plurality of cooling fins are provided so that, when viewed from the opposite side of the cylinder axis from the cam chain chamber, edges (on the cylinder axis) of those cooling fins which are located on the combustion chamber side of an apex of the combustion chamber wall are closer to the cylinder axis than are edges (on the cylinder axis side) of those cooling fins which are located on the opposite side of the apex of the combustion chamber wall from the combustion chamber. Since the cylinder-axis-side edges of those cooling fins which are located on the combustion chamber side of the apex of the combustion chamber wall are closer to the cylinder axis than are the cylinder-axis-side edges of those cooling fins which are located on the opposite side of the apex of the combustion chamber wall from the combustion chamber, i.e., the edges of the latter cooling fins are more distant from the cylinder axis than are the edges of the former cooling fins, the cross-sectional area of the cooling air duct can be increased further.

[0030] When a portion of the cooling air duct is defined by an exhaust duct wall which defines the exhaust duct and which intersects the cam chamber wall at an acute angle, the following advantage is provided. Usually, when forming the shape of the cooling air duct with a die at die casting, the portion of the die that corresponds to the cooling air duct is shaped so as to protrude from any other portion. The tip end of a portion with such a protruding shape is liable to high temperature due to the heat of the melt. In particular, if there is any corner in the tip end, the corner may be eroded; therefore, generally, the tip end is to be designed so as to have a circular cross section. However, by allowing a portion of the cooling air duct to be defined by the exhaust duct wall intersecting the cam chamber wall at an acute angle, the cross-sectional area of the cooling air duct can be increased. In this case, the problem of erosion can be avoided because the cam chamber wall and the exhaust duct wall may both have a small thickness.

[0031] Preferably, the cam chamber wall has a thickness of 2.5 mm or less. When the thickness of the cam chamber wall is 2.5 mm or less, erosion of die corners can be prevented with greater certainty. However, if the thickness of the cam chamber wall is less than 1.5 mm, the compressive strength that is required of the cam chamber may not be adequately obtained, thus resulting in an insufficient resistance against flow stress occurring due to distortion; therefore, it is preferable that the thickness of the cam chamber wall is 1.5 mm or more.

[0032] In the air-cooling type internal combustion engine according to the present invention, the cylinder head body is molded by die casting; therefore, the thickness and pitch of the cooling fins can be reduced, thus improving coolability. Specifically, the thickness of the leading edge of each cooling fin may be not less than 1.0 mm and not more than 2.5 mm, and the plurality of cooling fins may be disposed with a pitch of 7.5 mm or less, whereby coolability can be improved.

[0033] Preferably, each of the plurality of cooling fins has a draft of 2.0° or less. By ensuring that the draft is as small as 2.0° or less, the interspace at the feet of the cooling fins can be increased, whereby coolability can be further improved. However, from the standpoint of facilitating release, it is preferable that the draft of each the plurality of cooling fins is 1.0° or more.

[0034] Preferably, the cylinder head body includes a rib which is provided within the cooling air duct, the rib linking together the combustion chamber wall and the cam chamber wall. Since the rib links together the combustion chamber wall and the cam chamber wall, the rib is able to transmit the heat of the combustion chamber wall to the cam chamber wall, thus enabling cooling with the lubricating oil in the cam chamber, whereby coolability can be improved. Moreover, the rib being provided within the cooling air duct also provides a cooling effect with the cooling air.

[0035] Note that the rib is preferably formed along the release direction used when the cylinder head body is molded by die casting. Therefore, the rib is preferably formed along the wall portion (cooling air duct wall) defining the cooling air duct.

[0036] Moreover, it is preferable that a cross-sectional shape of the exhaust duct along a plane which is orthogonal to the axis of the exhaust duct is a substantial ellipse, and that the shape of the outlet of the exhaust duct is a substantially perfect circle. Since the cross-sectional shape of the exhaust pipe is generally a substantially perfect circle, the shape of the outlet of the exhaust duct being a substantially perfect circle will prevent abrupt changes in the duct area, thus preventing deterioration in the performance of the internal combustion engine. When the exhaust duct extends in such a manner that the exhaust duct becomes more distant from the cam chain chamber when going from the inlet side toward the outlet side, if the cross-sectional shape of the exhaust duct along a plane which is orthogonal to the axis were a substantially perfect circle, it would be impossible to shape the outlet of the exhaust duct in a substantially perfect circle. In contrast, ensuring that the cross-sectional shape of the exhaust duct along a plane which is orthogonal to the axis is a substantial ellipse (i.e., so that the circularity of the cross-sectional shape of the exhaust duct along a plane which is orthogonal to the axis is lower than the circularity of the shape of the outlet of the exhaust duct) allows the outlet of the exhaust duct to be shaped in a substantially perfect circle.

[0037] According to the present invention, there is provided an air-cooling type internal combustion engine including a cylinder head body which has a cooling air duct with a sufficient cross-sectional area and which can be suitably molded by die casting.

[0038] Additional benefits and advantages of the disclosed embodiments will be apparent from the specification and Figures. The benefits and/or advantages may be individually provided by the various embodiments and features of the specification and drawings disclosure, and need not all be provided in order to obtain one or more of the same.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 is a right side view schematically showing a motorcycle (saddled vehicle) 1 according to an embodiment of the present invention.

[0040] FIG. 2 is a cross-sectional view along line 2A-2A' in FIG. 1.

[0041] FIG. 3 is a diagram showing enlarged the vicinity of an engine (internal combustion engine) 101 which is shown in FIG. 2.

[0042] FIG. 4 is a right side view of a portion of the engine 101.

[0043] FIG. 5 is a cross-sectional left side view of the engine 101.

[0044] FIG. 6 is an upper plan view schematically showing a cylinder head body 100 which is included in the engine 101 according to an embodiment of the present invention.

[0045] FIG. 7 is a bottom view schematically showing a cylinder head body 100 which is included in the engine 101 according to an embodiment of the present invention.

[0046] FIG. 8 is a front view schematically showing a cylinder head body 100 which is included in the engine 101 according to an embodiment of the present invention.

[0047] FIG. 9 is a rear view schematically showing a cylinder head body 100 which is included in the engine 101 according to an embodiment of the present invention.

[0048] FIG. 10 is a left side view schematically showing a cylinder head body 100 which is included in the engine 101 according to an embodiment of the present invention.

[0049] FIG. 11 is a right side view schematically showing a cylinder head body 100 which is included in the engine 101 according to an embodiment of the present invention.

[0050] FIG. 12 is a cross-sectional view schematically showing a cylinder head body 100 which is included in the engine 101 according to an embodiment of the present invention, along line 12A-12A' in FIG. 11.

[0051] FIG. 13 is a cross-sectional view schematically showing a cylinder head body 100 which is included in the engine 101 according to an embodiment of the present invention, along line 13A-13A' in FIG. 7.

[0052] FIG. 14 is a diagram schematically showing a plurality of cooling fins 10 of the cylinder head body 100.

DETAILED DESCRIPTION

[0053] Hereinafter, with reference to the drawings, an embodiment of the present invention will be described. The present invention is not to be limited to the following embodiment.

[0054] FIG. 1 shows a saddled vehicle 1 according to the present embodiment. The saddled vehicle 1 shown in FIG. 1 is a motorcycle of a scooter type. Note that the saddled vehicle of the present invention is not limited to a scooter-type motorcycle 1. The saddled vehicle of the present invention may be any other type of motorcycle, e.g., a so-called moped type, an off-road type, or an on-road type. Moreover, the saddled vehicle of the present invention is meant to be any arbitrary vehicle which a rider sits astraddle, without being limited to two-wheeled vehicles. The saddled vehicle of the present invention may be a three-wheeled vehicle or the like of a type whose direction of travel is changed as the vehicle body is tilted, or any other saddled vehicle such as an ATV (All Terrain Vehicle).

[0055] In the following description, the front, rear, right, and left are respectively meant as the front, rear, right, and left as perceived by the rider of the motorcycle 1. Reference numerals F, Re, R, and L in the figures indicate front, rear, right, and left, respectively.

[0056] As shown in FIG. 1, the motorcycle 1 includes a vehicle main body 2, a front wheel 3, a rear wheel 4, and an engine unit 5 for driving the rear wheel 4. The vehicle main body 2 includes handle bars 6 which are controlled by the rider, and a seat 7 on which the rider sits. The engine unit 5 is an engine unit of a so-called unit-swing type, and is supported by a body frame (not shown in FIG. 1) so as to be capable of swinging around the pivot axis 8. In other words, the engine unit 5 is supported by the body frame in a manner capable of swinging.

[0057] Next, with reference to FIG. 2 to FIG. 5, the construction of the engine unit 5 of the motorcycle 1 will be described more specifically. FIG. 2 is a cross-sectional view along line 2A-2A' in FIG. 1. FIG. 3 is a diagram showing enlarged the vicinity of an engine 101 which is shown in FIG. 2. FIG. 4 is a right side view of a portion of the engine 101. FIG. 5 is a cross-sectional left side view of the engine 101.

[0058] 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. Although the engine 101 and the CVT 150 integrally compose the engine unit 5 in the example illustrated in FIG. 2, it will be appreciated that the engine 101 and the transmission may be separate.

[0059] The engine 101 is a single-cylinder engine having one cylinder. The engine 101 is a 4-stroke engine which sequentially repeats an intake step, a compression step, a combustion step, and an exhaust step. The engine 101 includes: a crankcase 102; a cylinder block 103 which extends frontward (as used herein, "frontward" not only means frontward in the strict sense, i.e., a direction which is parallel to the horizon, but also encompasses directions which are inclined from the horizon) from the crankcase 102 and is coupled to the crankcase 102; a cylinder head 104 which is connected in front of the cylinder block 103; and a cylinder head cover 105 connected in front of the cylinder head 104. A cylinder 106 is formed in the interior of the cylinder block 103.

[0060] Note that the cylinder 106 may be formed of a cylinder liner or the like which is inserted in the main body (i.e., the portion of the cylinder block 103 excluding the cylinder 106) of the cylinder block 103, and may be made integral with the main body of the cylinder block 103. In other words, the cylinder 106 may be made separable from the main body of the cylinder block 103, or inseparable from the main body of the cylinder block 103. A piston 107 is slidably accommodated in the cylinder 106. The piston 107 is disposed so as to be capable of reciprocation between a top dead center TDC and a bottom dead center BDC.

[0061] The cylinder head 104 is overlaid on the cylinder block 103 so as to cover the cylinder 106. The cylinder head 104 includes a cylinder head body 100 made of an aluminum alloy, a valve mechanism including a cam shaft 108, an intake valve 161, an exhaust valve 162, and the like. The valve mechanism is accommodated in a cam chamber 109. A portion 20 of the cylinder head body 100 that defines the cam chamber 20 is referred to as a cam chamber wall, as will be described later.

[0062] The cylinder head body 100, the top face of the piston 107, and the inner peripheral surface of the cylinder 106 together define a combustion chamber 110. A portion 30 of the cylinder head body 100 that defines the combustion chamber 110 is referred to as a combustion chamber wall, as will be described later.

[0063] The piston 107 is linked to a crankshaft 112 via a con' rod 111. The crankshaft 112 extends toward the left and the right, and is supported by a crankcase 102. The cam shaft 108 is driven by a cam chain 113 which is connected to the crankshaft 112. The cam chain 113 is accommodated in a cam chain chamber 70.

[0064] In the present embodiment, the crankcase 102, the cylinder block 103, the cylinder head 104, and the cylinder head cover 105 are separate pieces. However, they do not need to be separate pieces, and may be made integral as appropriate. For example, the crankcase 102 and the cylinder block 103 may be made integral, and the cylinder block 103 and the cylinder head 104 may be made integral. Moreover, the cylinder head 104 and the cylinder head cover 105 may be made integral.

[0065] As shown in FIG. 2, the CVT 150 includes: a first pulley 151, which is a driving pulley; a second pulley 152, which is a drone pulley; and a V-belt 153 which is wound around the first pulley 151 and the second pulley 152. The left end of the crankshaft 112 protrudes toward the left from the crankcase 102. The first pulley 151 is attached to the left end of the crankshaft 112. The second pulley 152 is attached to a main shaft 154. The main shaft 154 is linked to a rear wheel shaft 155 via a gear mechanism not shown. A transmission case 156 is provided to the left of the crankcase 102. The CVT 150 is accommodated in the transmission case 156.

[0066] An electric generator 120 is provided on the right-hand portion of the crankshaft 112. A cooling fan 121 is fixed at the right end of the crankshaft 112. The cooling fan 121 rotates together with the crankshaft 112. The cooling fan 121 is formed so as to suck air toward the left as it rotates. A shroud 130 is provided over the crankcase 102, the cylinder block 103, and the cylinder head 104. The electric generator 120 and the cooling fan 121 are accommodated within the shroud 130.

[0067] As shown in FIG. 4, the engine 101 is an engine of a type such that the cylinder block 103 and the cylinder head 104 are elongated in the horizontal direction or in a direction which is slightly inclined from the horizontal direction so as to rise toward the front, i.e., a so-called transverse type engine. Reference numeral L1 in the figure represents a line (cylinder axis) which passes through the center of the cylinder 106. The cylinder axis L1 extends in the horizontal direction or a direction slightly inclined from the horizontal direction. However, there is no particular limitation as to the direction of the cylinder axis L1. For example, the angle of tilt of the cylinder axis L1 with respect to the horizontal plane may be 0° to 15°, or greater than that. Reference numeral L2 in the figure represents the center line of the crankshaft 112.

[0068] 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 duct 40 and an exhaust duct 50 are formed in the interior of the cylinder head 104. The intake pipe 141 is connected to the intake duct 40, whereas the exhaust pipe 142 is connected to the exhaust duct 50. The intake valve 161 and the exhaust valve 162 are provided on the intake duct 40 and the exhaust duct 50, respectively.

[0069] The engine 101 according to the present embodiment is an air-cooled engine, which is cooled with air. As shown in FIG. 2 to FIG. 4, a plurality of cooling fins 114 are formed on the cylinder block 103. The cooling fins 114 extend in a direction which is substantially orthogonal to the cylinder axis L1. As will be described later, a plurality of cooling fins 10 (see FIG. 8 to FIG. 10) are also formed on the cylinder head body 100.

[0070] 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 with bolts 133. The inner member 131 and the outer member 132 are made of a synthetic resin, for example.

[0071] A hole 131a is formed in the inner member 131, in which an ignition 115 such as a spark plug is to be inserted. An air inlet 132a is formed in the outer member 132. When the shroud 130 is attached to the engine unit 5, the air inlet 132a is at a position opposing the cooling fan 121 (see FIG. 3). Reference numeral F in FIG. 4 indicates the outer periphery of the cooling fan 121, whereas reference numeral B indicates the direction of rotation of the cooling fan 121.

[0072] The shroud 130 is attached to the crankcase 102, the cylinder block 103, and the cylinder head 104, and extends frontward so as to fit along the cylinder block 103 and the cylinder head 104. The shroud 130 covers the right-hand portion of the crankcase 102, the cylinder block 103, and the cylinder head 104. Portions of the shroud 130 also partly cover an upper portion and a lower portion of the cylinder block 103 and the cylinder head 104.

[0073] When the cooling fan 121 rotates with the rotation of the crankshaft 112, the air which is external to the shroud 30 is introduced into the shroud 30 through the air inlet 132a. The air having been 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.

[0074] Next, with reference to FIG. 6 to FIG. 13, the construction of the cylinder head body 100 included in the engine 101 of the present embodiment will be specifically described. FIG. 6 and FIG. 7 are an upper plan view and a bottom view schematically showing the cylinder head body 100. FIG. 8 and FIG. 9 are a front view and a rear view schematically showing the cylinder head body 100. FIG. 10 and FIG. 11 are a left side view and a right side view schematically showing the cylinder head body 100. FIG. 12 is a cross-sectional view along line 12A-12A' in FIG. 11, and FIG. 13 is a cross-sectional view along line 8A-8A' in FIG. 7. The cylinder axis direction is indicated by arrow D1 in some of the figures. It will be appreciated that the cylinder axis direction is a direction which is parallel to the cylinder axis L1. In the following description, it is assumed that the side of the cylinder head body 100 at which the intake pipe 141 is connected will be regarded as the front side of the cylinder head body 100.

[0075] As shown in FIG. 6 to FIG. 13, the cylinder head body 100 includes the plurality of cooling fins 10, a cam chamber wall 20, and a combustion chamber wall 30. The cylinder head body 100 further includes the intake duct 40, the exhaust duct 50, and a cooling air duct 60.

[0076] As shown in FIG. 8, FIG. 9, and FIG. 10, the plurality of cooling fins 10 are provided on the outer side face (or more specifically, the left side face) of the cylinder head body 100, and formed so as to protrude out of the cylinder head body 100 (i.e., so as to extend in a direction substantially orthogonal to the cylinder axis direction D1). Moreover, the plurality of cooling fins 10 are disposed at a predetermined pitch along the cylinder axis direction D1. The number of cooling fins 10 is not limited to what is shown herein.

[0077] The cam chamber wall 20 (shown in FIG. 6, FIG. 10, and FIG. 13) defines the cam chamber 109. The cam chamber 109 accommodates the valve mechanism, including the cam shaft 108. The space existing between the cylinder head cover 105 attached to the upper portion of the cylinder head body 100 and the cam chamber wall 20 is the cam chamber 109.

[0078] The combustion chamber wall 30 (shown in FIG. 7, FIG. 10, and FIG. 13) defines the combustion chamber 110. The combustion chamber 110 is a space created by the combustion chamber wall 30 of the cylinder head body 100, the top face of the piston 107, and the inner peripheral surface of the cylinder 106. As shown in FIG. 7, not only an intake port 40a and an exhaust port 50a described below, but also a plug hole 32 is formed in the combustion chamber wall 30. The spark plug of the ignition 115 is attached in the plug hole 32.

[0079] The intake duct 40 is a passage through which air intake into the combustion chamber 110 occurs. An opening 40a of the intake duct 40 in the combustion chamber wall 30 is the intake port. As the intake valve 161 is moved up and down by the valve mechanism, the intake port 40a is opened or closed. To an opening 40b of the intake duct 40 at the opposite side from the combustion chamber wall 30 (located in the front of the cylinder head body 100), the intake pipe 141 is connected.

[0080] The exhaust duct 50 is a passage through which exhaust from the combustion chamber 110 occurs. An opening 50a of the exhaust duct 50 in the combustion chamber wall 30 is the exhaust port. As the exhaust valve 162 is moved up and down by the valve mechanism, the exhaust port 50a is opened or closed. To an opening 50b of the exhaust duct 50 at the opposite side from the combustion chamber wall 30, the exhaust pipe 142 is connected.

[0081] Typically, the plurality of cooling fins 10 include those cooling fins 10 which extend from an exhaust duct wall defining the exhaust duct 50 (located on the relatively right-hand side in FIG. 10). In the present embodiment, the plurality of cooling fins 10 further include those cooling fins 10 which extend from an intake duct wall defining the intake duct 40 (located on the relatively left-hand side in FIG. 10).

[0082] The cooling air duct 60 (shown in FIG. 10 and FIG. 13) is a passage for allowing cooling air to pass through between the cam chamber wall 20 and the combustion chamber wall 30. As shown in FIG. 7, an inlet 60a of the cooling air duct 60 is located on the left side face of the cylinder head body 100, whereas an outlet 60b of the cooling air duct 60 is located on the right side face of the cylinder head body 100. The cooling air CA which has been introduced by the cooling fan 121 into the shroud 130 is introduced through the inlet 60a into the cooling air duct 60, cools down the cylinder head body 100 as it passes through the cooling air duct 60, and thereafter is discharged through the outlet 60b to the exterior of the cylinder head body 100.

[0083] The cylinder head body 100 is integrally molded from an aluminum alloy by die casting. As the aluminum alloy, ADC10 or ADC12 is suitably used, for example.

[0084] As shown in FIG. 6, FIG. 7, and FIG. 12, the cylinder head body 100 further includes the cam chain chamber 70 for accommodating the cam chain 113. The cam chain 113 is a member with which to drive the cam shaft 108 of the valve mechanism.

[0085] The exhaust duct 50 extends in such a manner that, when viewed in the cylinder axis direction D1 (i.e., a direction which is perpendicular to the plane of the figure of FIG. 6, FIG. 7, and FIG. 12), the exhaust duct 50 becomes more distant from the cam chain chamber 70 when going from the inlet (exhaust port 50a) toward the outlet (opening 50b). In other words, an axis 50x of the exhaust duct 50 is inclined with respect to the front-rear direction of the cylinder head body 100. Moreover, the exhaust duct 50 is formed so that, when viewed in the cylinder axis direction D1, its axis 50x appears linear.

[0086] Moreover, as shown in FIG. 6, FIG. 7, and FIG. 12, the cylinder head body 100 has a plurality of bolt holes 80a to 80d, into each of which a head bolt is inserted. The head bolts (which typically are stud bolts) inserted in the bolt holes 80a to 80d cause the cylinder head body 100 to be coupled to the cylinder block 103. Among the plural (i.e., 4 herein) bolt holes 80a to 80d, one bolt hole (the bolt hole which appears upper right in FIG. 6 and FIG. 12 and lower right in FIG. 7) 80a is provided between the exhaust duct 50 and the cam chain chamber 70. A portion of the cooling air duct 60 is located between this bolt hole 80a and the exhaust duct 50. Bosses 80 having the bolt holes 80a to 80d may be referred to as bosses for head bolts or bosses for stud bolts.

[0087] As mentioned earlier, the cylinder head body 100 of the engine (internal combustion engine) 101 according to an embodiment of the present invention is integrally molded by die casting. In other words, unlike the cylinder head of Patent Document 1, there are no liners, as separate members, being cast together in the cylinder head body 100. Therefore, no misalignments of the intake duct 40 and the exhaust duct 50 will be caused by liner misalignments, so that deterioration in the performance of the engine 101 associated with misalignments of the intake duct 40 and the exhaust duct 50 can be prevented.

[0088] Moreover, since the exhaust duct 50 extends in such a manner that the exhaust duct 50 becomes more distant from the cam chain chamber 70 when going from the inlet side toward the outlet side, the space between the outlet of the exhaust duct 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 duct 60. This realizes a sufficiently high coolability.

[0089] Furthermore, the exhaust duct 50 is formed so that its axis 50x is linear. Thus, exhaust resistance can be reduced, and a more efficient combustion is enabled. Moreover, when molding the cylinder head body 100 by die casting, the exhaust duct 50 in its final shape can be formed with a die, which makes it unnecessary to employ subsequent machining to change the shape of the exhaust duct 50.

[0090] From the standpoint of securing a sufficiently large cross-sectional area of the cooling air duct 60, it is preferable that the axis 50x of the exhaust duct 50 is inclined at a somewhat large angle with respect to the front-rear direction. Specifically, it is preferable that, when viewed in the cylinder axis direction D1, the axis 50x of the exhaust duct 50 is inclined at an angle of 20° or more with respect to a line L3 connecting the centers of the two bolt holes 80a and 80b that are located closer to the cam chain chamber 70 among the four bolt holes 80a to 80d. However, if the angle of tilt is too large, the exhaust resistance may become excessive; therefore, the angle of tilt is preferably 30° or less.

[0091] As in the present embodiment, when a certain bolt hole 80a among the plurality of bolt holes 80a to 80d is provided between the exhaust duct 50 and the cam chain chamber 70, it is necessary that a portion of the cooling air duct 60 be located (disposed) in a space which is narrower than that between the exhaust duct 50 and the cam chain chamber 70 (i.e., a space between the bolt hole 80a and the exhaust duct 50). However, as described above, the exhaust duct 50 extends in such a manner that the exhaust duct 50 becomes more distant from the cam chain chamber 70 when going from the inlet side toward the outlet side; therefore, a sufficiently cross-sectional area of the cooling air duct 60 can be ensured also between the bolt hole 80a and the exhaust duct 50.

[0092] When the shape of the exhaust duct 50 is designed so that its axis 50x is linear, it is easy to form the exhaust duct 50 by using a die, without using any cores. By forming the exhaust duct 50 with a die, it is possible to make the surface roughness of the inner peripheral surface of the exhaust duct 50 smaller than that when cores are used. More specifically, the surface roughness Rz (maximum height) of the inner peripheral surface of the exhaust duct 50 can be made 30 µm or less, thus reducing exhaust resistance and improving the output power of the engine 101. By also ensuring that the surface roughness Rz of the inner peripheral surface of the intake duct 40 is 30 µm or less, intake resistance can be reduced to further improve the output power of the engine 101.

[0093] Preferably, the plurality of cooling fins 10 include those cooling fins 10 which extend from the exhaust duct wall defining the exhaust duct 50. Since the exhaust duct 50 is one place in the cylinder head body 100 that is liable to high temperature, the cooling fins 10 extending from the exhaust duct wall will allow for an improved cooling efficiency. From the standpoint of ensuring a sufficiently high cooling efficiency, more specifically, the cooling fins 10 extending from the exhaust duct wall may extend at least from a portion of the exhaust duct wall that is located closer to the cylinder axis L1 than is the boss (boss for stud bolt) 80 corresponding to the bolt hole (the closest bolt hole to the cooling fins 10 extending from the exhaust duct wall) 80c (see FIG. 10).

[0094] Now, among the plurality of cooling fins 10, those cooling fins 10a which are located on the combustion chamber 110 side of an apex of the combustion chamber wall 30 will be referred to as "first cooling fins", and those cooling fins 10b which are located on the opposite side of the apex of the combustion chamber wall 30 from the combustion chamber 110 (i.e., so as to be closer to the cam chamber) will be referred to as "second cooling fins". In the present embodiment, as can be seen from FIG. 8, FIG. 9, and FIG. 10, the plurality of cooling fins 10 are provided in such a manner that a total area of the first cooling fins 10a is greater than a total area of the second cooling fins 10b.

[0095] During the operation of the engine 101, within the cylinder head body 100, the region which is on the combustion chamber 110 side of the apex of the combustion chamber wall 30 has a higher temperature than the region on the opposite side of the apex of the combustion chamber wall 30 from the combustion chamber 110. Therefore, coolability can be efficiently improved by ensuring that a total area of the first cooling fins 10a located in the former region is greater than a total area of the second cooling fins 10b located in the latter region.

[0096] Moreover, in the present embodiment, as shown in FIG. 10, the plurality of cooling fins 10 are provided so that, when viewed from the opposite side of the cylinder axis L1 from the cam chain chamber 70 (i.e., from a direction perpendicular to the plane of the figure of FIG. 10), edges 10a1 of the first cooling fins 10a on the cylinder axis L1 side are closer to the cylinder axis L1 than are edges 10b1 of the second cooling fins 10b on the cylinder axis L1 side. In other words, the edges 10b1 of the second cooling fins 10b are more distant from the cylinder axis L1 than are the edges 10a1 of the first cooling fins 10a. This allows the cross-sectional area of the cooling air duct 60 to be increased further.

[0097] Furthermore, in the present embodiment, as shown in FIG. 10, a portion of the cooling air duct 60 is defined by an exhaust duct wall 51 which defines the exhaust duct 50 and which intersects the cam chamber wall 20 at an acute angle. This provides the following advantage.

[0098] Usually, when forming the shape of the cooling air duct with a die at die casting, the portion of the die that corresponds to the cooling air duct is shaped so as to protrude from any other portion. The tip end of a portion with such a protruding shape is liable to high temperature due to the heat of the melt. In particular, if there is any corner in the tip end, the corner may be eroded; therefore, generally, the tip end is to be designed so as to have a circular cross section. However, as in the present embodiment, by allowing a portion of the cooling air duct 60 to be defined by the exhaust duct wall 51 intersecting the cam chamber wall 20 at an acute angle, the cross-sectional area of the cooling air duct 60 can be increased. In this case, the problem of erosion can be avoided because the cam chamber wall 20 and the exhaust duct wall 51 may both have a small thickness.

[0099] Preferably, the cam chamber wall 20 has a thickness of 2.5 mm or less. When the thickness of the cam chamber wall 20 is 2.5 mm or less, erosion of die corners can be prevented with greater certainty. However, if the thickness of the cam chamber wall 20 is less than 1.5 mm, the compressive strength that is required of the cam chamber 109 may not be adequately obtained, thus resulting in an insufficient resistance against flow stress occurring due to distortion; therefore, it is preferable that the thickness of the cam chamber wall 20 is 1.5 mm or more.

[0100] Moreover, in the present embodiment, the cylinder head body 100 is molded by die casting; therefore, the thickness and pitch of the cooling fins 10 can be reduced, thus improving coolability. Specifically, as shown in FIG. 14, given a thickness t of the leading edge of each of the plurality of cooling fins 10, and a pitch p of the plurality of cooling fins 10, the thickness t of the leading edge of each cooling fin 10 may be not less than 1.0 mm and not more than 2.5 mm, and the plurality of cooling fins 10 may be disposed with a pitch p of 7.5 mm or less.

[0101] Preferably, each of the plurality of cooling fins 10 has a draft of 2.0° or less. By ensuring that the draft is as small as 2.0° or less, the interspace at the feet of the cooling fins 10 can be increased, whereby coolability can be further improved. However, from the standpoint of facilitating release, it is preferable that the draft of each of the plurality of cooling fins 10 is 1.0° or more.

[0102] Moreover, as shown in FIG. 10, the cylinder head body 100 of the present embodiment further includes a rib 90 which is provided within the cooling air duct 60, the rib 90 linking together the combustion chamber wall 30 and the cam chamber wall 20. Since the rib 90 links together the combustion chamber wall 30 and the cam chamber wall 20, the rib 90 is able to transmit the heat of the chamber wall 30 to the cam chamber wall 20, thus enabling cooling with the lubricating oil in the cam chamber 109, whereby coolability can be improved. Moreover, the rib 90 being provided within the cooling air duct 60 also provides a cooling effect with the cooling air CA.

[0103] Note that the rib 90 is preferably formed along the release direction used when the cylinder head body 100 is molded by die casting. Therefore, the rib 90 is preferably formed along the wall portion (cooling air duct wall) defining the cooling air duct 60.

[0104] Moreover, it is preferable that a cross-sectional shape of the exhaust duct 50 along a plane which is orthogonal to the axis 50x of the exhaust duct 50 is a substantial ellipse, and that the shape of the outlet 50b of the exhaust duct 50 is a 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 shape of the outlet 50b of the exhaust duct 50 being a substantially perfect circle will prevent abrupt changes in the duct area, thus preventing deterioration in the performance of the engine 101. As has already been described, the exhaust duct 50 extends in such a manner that the exhaust duct 50 becomes more distant from the cam chain chamber 70 when going from the inlet side toward the outlet side; therefore, if the cross-sectional shape of the exhaust duct 50 along a plane which is orthogonal to the axis 50x were a substantially perfect circle, it would be impossible to shape the outlet 50b of the exhaust duct 50 in a substantially perfect circle. Ensuring that the cross-sectional shape of the exhaust duct 50 along a plane which is orthogonal to the axis 50x is a substantial ellipse (i.e., so that the circularity of the cross-sectional shape of the exhaust duct 50 along a plane which is orthogonal to the axis 50x is lower than the circularity of the shape of the outlet 50b of the exhaust duct 50) allows the outlet 50b of the exhaust duct 50 to be shaped in a substantially perfect circle.

[0105] Furthermore, it is preferable to perform a shot blast treatment for any wall portion defining the cooling air duct 60 and the cam chain chamber 109, and the outer side faces including the plurality of cooling fins 10. Roughening achieved through a shot blast treatment will allow for an increased area of contact with the cooling air CA, thus enabling a further enhancement in coolability. Moreover, the cooling air duct 60 may also be deburred through the shot blast treatment.

[0106] Moreover, for further improvement in coolability, it would be preferable to provide cooling fins extending from the rib 90, or perform a shot blast treatment for the rib 90.

[0107] The internal combustion engine 101 according to an embodiment of the present invention is suitably used for various saddled vehicles such a motorcycles and ATVs (All Terrain Vehicles). It is also suitably used for electric generators or the like.

[0108] According to the present invention, there is provided an air-cooling type internal combustion engine including a cylinder head body which has a cooling air duct with a sufficient cross-sectional area and which can be suitably molded by die casting. An air-cooling type internal combustion engine according to the present invention provides excellent coolability of the cylinder head body, and is suitably used for various saddled vehicles such as motorcycles.

[0109] While the present invention has been described with respect to exemplary embodiments thereof, it will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than those specifically described above. Accordingly, it is intended by the appended claims to cover all modifications of the invention that fall within the true spirit and scope of the invention.

Claims

1. An air-cooling type internal combustion engine comprising a cylinder head body, the cylinder head body including:

a plurality of cooling fins;

a cam chamber wall defining a cam chamber;

a combustion chamber wall defining a combustion chamber;

an intake duct through which air intake into the combustion chamber is to occur;

an exhaust duct through which exhaust from the combustion chamber is to occur; and

a cooling air duct for allowing cooling air to pass through between the cam chamber wall and the combustion chamber wall, wherein,

the cylinder head body is integrally molded from an aluminum alloy by die casting;

the cylinder head body further includes a cam chain chamber for accommodating a cam chain; and

when viewed in a cylinder axis direction, the exhaust duct extends in such a manner that the exhaust duct becomes more distant from the cam chain chamber when going from an inlet side toward an outlet side and the exhaust duct is formed so that an axis of the exhaust duct is linear.

2. The air-cooling type internal combustion engine of claim 1, wherein the plurality of cooling fins include a cooling fin extending from an exhaust duct wall defining the exhaust duct.

3. The air-cooling type internal combustion engine of claim 1 or 2, wherein an inner peripheral surface of the exhaust duct has a surface roughness Rz of 30 µm or less.

4. The air-cooling type internal combustion engine of any of claims 1 to 3, wherein,
the cylinder head body further includes a plurality of bolt holes, into each of which a head bolt is to be inserted;
one of the plurality of bolt holes is provided between the exhaust duct and the cam chain chamber; and
a portion of the cooling air duct is located between the one bolt hole and the exhaust duct.

5. The air-cooling type internal combustion engine of any of claims 1 to 4, wherein the plurality of cooling fins are provided in such a manner that a total area of those cooling fins which are located on the combustion chamber side of an apex of the combustion chamber wall is greater than a total area of those cooling fins which are located on an opposite side of the combustion chamber from the apex of the combustion chamber wall.

6. The air-cooling type internal combustion engine of any of claims 1 to 5, wherein the plurality of cooling fins are provided so that, when viewed from an opposite side of the cylinder axis from the cam chain chamber, cylinder-axis-side edges of those cooling fins which are located on the combustion chamber side of the apex of the combustion chamber wall are closer to the cylinder axis than are cylinder-axis-side edges of those cooling fins which are located on an opposite side of the apex of the combustion chamber wall from the combustion chamber.

7. The air-cooling type internal combustion engine of any of claims 1 to 6, wherein a portion of the cooling air duct is defined by an exhaust duct wall defining the exhaust duct, the exhaust duct wall intersecting the cam chamber wall at an acute angle.

8. The air-cooling type internal combustion engine of claim 7, wherein the cam chamber wall has a thickness of not less than 1.5 mm and not more than 2.5 mm.

9. The air-cooling type internal combustion engine of any of claims 1 to 8, wherein,
a leading edge of each of the plurality of cooling fins has a thickness of not less than 1.0 mm and not more than 2.5 mm; and
the plurality of cooling fins are disposed with a pitch of 7.5 mm or less.

10. The air-cooling type internal combustion engine of any of claims 1 to 9, wherein each of the plurality of cooling fins has a draft of not less than 1.0° and not more than 2.0°.

11. The air-cooling type internal combustion engine of any of claims 1 to 10, wherein the cylinder head body further includes a rib which is provided within the cooling air duct, the rib linking together the combustion chamber wall and the cam chamber wall.

12. The air-cooling type internal combustion engine of claim 11, wherein the rib is formed along a cooling air duct wall defining the cooling air duct.

13. The air-cooling type internal combustion engine of any of claims 1 to 12, wherein a circularity of a cross-sectional shape of the exhaust duct along a plane which is orthogonal to the axis of the exhaust duct is lower than a circularity of the shape of an outlet of the exhaust duct.

14. The air-cooling type internal combustion engine of claim 13, wherein the cross-sectional shape of the exhaust duct along the plane which is orthogonal to the axis of the exhaust duct is a substantial ellipse, and the shape of the outlet of the exhaust duct is a substantially perfect circle.

15. A saddled vehicle comprising the air-cooling type internal combustion engine of any of claims 1 to 14.

Drawing