EP2743487B1

EP2743487B1 - Forced air-cooling type internal combustion engine and saddled vehicle having the same

Info

Publication number: EP2743487B1
Application number: EP13188290.4A
Authority: EP
Inventors: Satoshi Kumagai
Original assignee: Yamaha Motor Co Ltd
Current assignee: Yamaha Motor Co Ltd
Priority date: 2012-12-12
Filing date: 2013-10-11
Publication date: 2017-03-01
Anticipated expiration: 2033-10-11
Also published as: PH12013000370B1; EP2743487A1; TW201422902A; CN103867326B; CN103867326A; PH12013000370A1; TWI551775B; MY166099A; JP2014114790A; ES2619306T3

Description

BACKGROUND

1. Technical Field:

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

2. Description of the Related Art:

Internal combustion engines for saddled vehicles are generally classified into the water-cooling type and the air-cooling type. The water-cooling type achieves cooling by using a coolant (such as water) as a medium, whereas the air-cooling type achieves cooling with air. In an air-cooling type internal combustion engine, a multitude of cooling fins are provided on the surface of the internal combustion engine for improving the cooling efficiency (see, for example Japanese Laid-Open Patent Publication No. 2010-159703 (hereinafter, "Patent Document 1").
In FR2 393 941 , which is also the basis for the preamble of the invention it is disclosed to provide cooling fins to the engine and to provide a fan so that the air is vented through the channels of the cooling fins.
Among air-cooling type internal combustion engines, natural air-cooling type internal combustion engines and forced air-cooling type internal combustion engines are known. The natural air-cooling type achieves cooling as the cooling fins receive air resistance during travel. The internal combustion engine disclosed in Patent Document 1 is a natural air-cooling type. On the other hand, in the forced air-cooling type, a fan is driven by the motive power of the internal combustion engine, such that the cooling fins receive the cooling air which is introduced by the fan to the inside of the shroud (cowling), whereby cooling is achieved.
The inventors have studied cooling fin structures that may be optimum for internal combustion engines of the forced air-cooling type. Specifically, the inventors have considered reducing the thickness and pitch of cooling fins (i.e., placing thin cooling fins at narrow interspaces) to provide as many cooling fins as possible on the cylinder head and the cylinder block, thus enhancing cooling efficiency. As a result, the inventors have found that disposing thin cooling fins at narrow interspaces may enhance cooling efficiency, but, when the cylinder head or cylinder block is molded through casting, melt permeability around the cooling fins may be lowered, thus possibly causing casting insufficiencies.

SUMMERY

The present invention has been made in view of the above problems, and an objective thereof is to provide a forced air-cooling type internal combustion engine which excels in both castability and cooling efficiency of a cylinder head and/or a cylinder block.
A forced air-cooling type internal combustion engine according to the present invention comprises: a cylinder block molded by casting; a cylinder head molded by casting and overlaid on the cylinder block; further including a cooling air duct; a shroud covering at least a portion of the cylinder block and at least a portion of the cylinder head; and a fan for rotating to introduce air to an inside of the shroud, wherein, at least one of the cylinder block and the cylinder head includes a cooling fin formed at least in a portion covered by the shroud and a cross fin provided so as to cross the cooling fin, the cross fin being connected to the cooling fin; and a thickness of the cross fin at a leading edge thereof is greater than a thickness of the cooling fin at a leading edge thereof, wherein the corss fin overlaps with the combustion chamber when viewed in a cylinder axis direction, and which is connected to a combustion chamber wall; wherein the forced air-cooling type internal combustion engine further comprises a cam shaft provided above a combustion chamber wall, and the cooling air duct is located between the cam shaft and the combustion chamber wall.
In a preferred embodiment, between the cylinder block and the cylinder head, at least the cylinder head includes the cross fin.
In a preferred embodiment, the cross fin is at an angle of 45° or less with respect to an axis of rotation of the fan when viewed in a cylinder axis direction.
A preferred embodiment further comprises a plurality of head bolts for coupling the cylinder block and the cylinder head, wherein, the plurality of head bolts include two head bolts that are located on the fan side of a cylinder axis; and the cross fin is located in part between the two head bolts.
In a preferred embodiment, the width of the cross fin along a cylinder axis direction is smaller at the leading edge of the cross fin than at a foot of the cross fin.
In a preferred embodiment, the thickness of the cross fin increases from the leading edge toward the foot of the cross fin.
In a preferred embodiment, the thickness of the cross fin increases toward the cylinder block.
In a preferred embodiment, a parting line of at least one of the cylinder block and the cylinder head is located between a center of the cooling fin and the leading edge of the cooling fin.
In a preferred embodiment, at least one of the cylinder block and the cylinder head includes a plurality of cooling fins; and, given a thickness t (mm) of each of the plurality of cooling fins at the leading edge and an interspace c (mm) between the leading edges of any two adjacent cooling fins among the plurality of cooling fins, the thickness t and the interspace c satisfy the relationships t ≦ 3 and t ≦ c ≦ 3t.
In a preferred embodiment, the thickness t further satisfies the relationship 1 ≦ t.
In a preferred embodiment, the interspace c further satisfies the relationship 3 ≦ c.
In a preferred embodiment, the cooling fin has a draft of not more than 1.0° and not less than 2.0°.
A saddled vehicle according to the present invention comprises a forced air-cooling type internal combustion engine of the above construction.
The internal combustion engine according to the present invention is a forced air-cooling type internal combustion engine having a shroud and a fan. Therefore, even when the thickness and pitch of the cooling fins are reduced (i.e., thin cooling fins are placed at narrow interspaces) in order to allow as many cooling fins as possible to be provided for an improved cooling efficiency, it is still possible to send sufficient cooling air through the gaps between adjacent cooling fins. Moreover, in the forced air-cooling type internal combustion engine according to the present invention, at least one of the cylinder block and the cylinder head includes not only cooling fins, but also cross fins which are provided so as to cross the cooling fins and which are connected to the cooling fins. The thickness of the cross fins at the leading edges is greater than the thickness of the cooling fins at the leading edges. Since such cross fins are provided, even if thin cooling fins are placed at narrow interspaces for an improved cooling efficiency, deterioration in melt permeability at casting can be prevented, thereby preventing casting insufficiencies. Thus, the forced air-cooling type internal combustion engine according to the present invention excels in both castability and cooling efficiency of the cylinder head and/or the cylinder block.
Preferably, between the cylinder block and the cylinder head, at least the cylinder head includes cross fins. Generally, a cylinder head is likely to have a more complicated shape than a cylinder block; therefore, if thin cooling fins are placed at narrow interspaces, melt permeability around the cooling fins is likely to be deteriorated. By providing the cross fins at least on the cylinder head, casting insufficiencies can be effectively prevented.
When the cross fins are provided at an angle of 45° or less with respect to an axis of rotation of the fan as viewed in the cylinder axis direction, the cross fins are unlikely to present resistance against the cooling air which is sent from the fan. Thus, deterioration in cooling efficiency due to the provision of the cross fins can be prevented.
Preferably, the cross fins overlap with the combustion chamber when viewed in the cylinder axis direction. In other words, it is preferable that the cross fins are connected to the combustion chamber wall defining the combustion chamber. When the cross fins are provided in this manner, the heat generated in the combustion chamber can be transmitted to the cooling fins via the cross fins, thereby improving the cooling efficiency.
Typically, the internal combustion engine according to the present invention includes a plurality of head bolts that couple the cylinder block and the cylinder head, the plurality of head bolts including two head bolts that are located on the fan side of the cylinder axis. Preferably, the cross fins are located in part between these two head bolts. Thus placed, the cross fins are close to the center of the combustion chamber, allowing more heat to be transmitted to the cooling fins via the cross fins; as a result, a further enhancement in cooling efficiency is achieved.
When the width of each cross fin along the cylinder axis direction is smaller at the leading edge of the cross fin than at the foot of the cross fin, it is possible to provide a large number of cooling fins at the leading edge side, while allowing at the foot side the cam chamber to be placed near the combustion chamber, thus downsizing the cylinder head. In other words, both coolability and downsizing are reconciled.
Preferably, the thickness of each cross fin increases from the leading edge toward the foot of the cross fin. The thickness of the cross fins thus being set allows more heat to be transmitted from the combustion chamber to the cooling fins.
Moreover, it is preferable that the thickness of the cross fins increases toward the cylinder block. The thickness of the cross fins thus being set allows more heat to be transmitted from the combustion chamber to the cooling fins.
Preferably, a parting line (i.e., the position at which the mold is parted in casting) of the cylinder block and/or the cylinder head is somewhere between the center and the leading edge of each cooling fin. When the parting line is at such a position, burrs at the parting line are easy to remove. On the other hand, if the parting line is somewhere between the center and the foot of each cooling fin, the deburring work will become difficult.
Preferably, the relationships t ≦ 3 and t ≦ c ≦ 3t are satisfied by the thickness t (mm) of each of the plurality of cooling fins at the leading edge and the interspace c (mm) between the leading edges of any two adjacent cooling fins among the plurality of cooling fins. By placing thin cooling fins at narrow interspaces while satisfying these relationships, it becomes possible to provide a large number of cooling fins, thereby improving the cooling efficiency.
Preferably, the thickness t of the cooling fins at the leading edges satisfies the relationship 1 ≦ t. As the thickness of the cooling fins decreases, more cooling fins can be provided; however, if the thickness of the cooling fins is too small, it will be difficult to take heat away from the cylinder block and the cylinder head. This problem does not occur when the thickness t of the cooling fins at the leading edges is 1 mm or more (i.e., 1 ≦ t).
Preferably the interspace c between the leading edges of any two adjacent cooling fins satisfies the relationship 3 ≦ c. When the interspace c between the leading edges of any two adjacent cooling fins is 3 mm or more (i.e., 3 ≦ c), it is easy to supply cooling air to the feet of the cooling fins, whereby the cooling efficiency is improved.
Preferably, the cooling fins have a draft of 2.0° or less. By ensuring that the draft is as small as 2.0° or less, it becomes possible to increase the interspace at the feet of the cooling fins, thereby further improving coolability. However, from the standpoint of facilitating release, it is preferable that the draft of the cooling fins is 1.0° or more.
According to the present invention, there is provided a forced air-cooling type internal combustion engine which excels in both castability and cooling efficiency of a cylinder head and/or a cylinder block.
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

FIG. 1 is a right side view schematically showing a motorcycle (saddled vehicle) 1 according to an embodiment of the present invention.
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 (internal combustion 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.
FIG. 6 is an upper plan view schematically showing a cylinder head 100 which is included in the engine 101 according to an embodiment of the present invention.
FIG. 7 is a bottom view schematically showing a cylinder head 100 which is included in the engine 101 according to an embodiment of the present invention.
FIG. 8 is a front view schematically showing a cylinder head 100 which is included in the engine 101 according to an embodiment of the present invention.
FIG. 9 is a rear view schematically showing a cylinder head 100 which is included in the engine 101 according to an embodiment of the present invention.
FIG. 10 is a left side view schematically showing a cylinder head 100 which is included in the engine 101 according to an embodiment of the present invention.
FIG. 11 is a right side view schematically showing a cylinder head 100 which is included in the engine 101 according to an embodiment of the present invention.
FIG. 12 is a cross-sectional view schematically showing a cylinder head 100 which is included in the engine 101 according to an embodiment of the present invention, along line 12A-12A' in FIG. 10 .
FIG. 13A is a cross-sectional view schematically showing cooling fins 10 of the cylinder head 100; and FIG. 13B is a cross-sectional view schematically showing a cross fin 20 of the cylinder head 100.

DETAILED DESCRIPTION

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.
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).
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.
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.
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.
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.
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 100 which is connected in front of the cylinder block 103; and a cylinder head cover 105 connected in front of the cylinder head 100.
The cylinder block 103 is molded by casting (e.g., gravity casting). The material of the cylinder block 103 is an aluminum alloy or a cast iron, for example. A cylinder 106 is formed in the interior of the cylinder block 103.
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.
The cylinder head 100 is overlaid on the cylinder block 103 so as to cover the cylinder 106. The cylinder head 100 is molded by casting (e.g., gravity casting). The material of the cylinder head 100 is an aluminum alloy or a cast iron, for example. The cylinder head 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 100 that defines the combustion chamber 110 is referred to as a combustion chamber wall.
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.
In the present embodiment, the crankcase 102, the cylinder block 103, the cylinder head 100, 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 100 may be made integral. Moreover, the cylinder head 100 and the cylinder head cover 105 may be made integral.
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.
An electric generator 120 is provided on the right-hand portion of the crankshaft 112. A cooling fan (hereinafter simply referred to as a "fan") 121 is fixed at the right end of the crankshaft 112. The fan 121 rotates together with the crankshaft 112. The fan 121 is formed so as to suck air toward the left as it rotates. The electric generator 120 and the fan 121 are accommodated within a shroud 130. The shroud 130 is provided so as to cover at least a portion of the cylinder block 103 and at least a portion of the cylinder head 100.
As shown in FIG. 4 , the engine 101 is an engine of a type such that the cylinder block 103 and the cylinder head 100 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.
An intake pipe 141 is connected to an upper portion of the cylinder head 100. An exhaust pipe 142 is connected to a lower portion of the cylinder head 100. An intake duct 40 and an exhaust duct 50 are formed in the interior of the cylinder head 100. 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.
The engine 101 according to the present embodiment is an air-cooled engine, or more specifically a forced air-cooling type engine, which is cooled with air. As shown in FIG. 2 to FIG. 4 , the cylinder block 103 includes a plurality of cooling fins 114 which are formed at least in a portion that is covered by the shroud 130. The cooling fins 114 extend in a direction which is substantially orthogonal to the cylinder axis L1. As will be described later, the cylinder head 100 also includes a plurality of cooling fins 10 which are formed at least in a portion that is covered by the shroud 130 (see FIG. 8 to FIG. 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 with bolts 133. The inner member 131 and the outer member 132 are made of a synthetic resin, for example.
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 fan 121 (see FIG. 3 ). Reference numeral F in FIG. 4 indicates the outer periphery of the fan 121, whereas reference numeral B indicates the direction of rotation of the fan 121.
The shroud 130 is attached to the crankcase 102, the cylinder block 103, and the cylinder head 100, and extends frontward so as to fit along the cylinder block 103 and the cylinder head 100. The shroud 130 covers the right-hand portion of the crankcase 102, the cylinder block 103, and the cylinder head 100. Portions of the shroud 130 also partly cover an upper portion and a lower portion of the cylinder block 103 and the cylinder head 100.
When the fan 121 rotates with the rotation of the crankshaft 112, the air which is external to the shroud 130 is introduced into the shroud 130 through the air inlet 132a. The air having been introduced into the shroud 130 is blown onto the cylinder block 103 and the cylinder head 100. The cylinder block 103 and the cylinder head 100 are cooled by this air.
Next, with reference to FIG. 6 to FIG. 12 , the construction of the cylinder head 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 100. FIG. 8 and FIG. 9 are a front view and a rear view schematically showing the cylinder head 100. FIG. 10 and FIG. 11 are a left side view and a right side view schematically showing the cylinder head 100. FIG. 12 is a cross-sectional view along line 12A-12A' in FIG. 10 . 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 100 at which the intake pipe 141 is connected will be regarded as the front side of the cylinder head 100.
As shown in FIG. 6 to FIG. 12 , the cylinder head 100 includes the plurality of cooling fins 10, a combustion chamber wall 30, an intake duct 40, an exhaust duct 50, and a cooling air duct 60.
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 100, and formed so as to protrude out of the cylinder head 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.
The combustion chamber wall 30 (shown in FIG. 7 and FIG. 10 ) defines the combustion chamber 110. The combustion chamber 110 is a space created by the combustion chamber wall 30 of the cylinder head 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.
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, 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 100), the intake pipe 141 is connected.
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, 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.
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 ).
The cooling air duct 60 (shown in FIG. 10 ) is a passage for allowing cooling air to pass through. 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 100, whereas an outlet 60b of the cooling air duct 60 is located on the right side face of the cylinder head 100. The cooling air CA which has been introduced by the fan 121 into the shroud 130 is introduced through the inlet 60a into the cooling air duct 60, cools down the cylinder head 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 100.
Moreover, as shown in FIG. 6 , FIG. 7 , and FIG. 12 , the cylinder head 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 100 to be coupled to the cylinder block 103. Bosses 80 having the bolt holes 80a to 80d may be referred to as bosses for head bolts or bosses for stud bolts.
The cylinder head 100 further includes cross fins 20 provided so as to cross the cooling fins 10, the cross fins 20 being connected to the cooling fins 10. In the present embodiment, two cross fins 20 are provided. One of the two cross fins 20 (the one that is located relatively closer to the exhaust duct 50 side in FIG. 10 ) is connected to the cooling fins 10 extending from the exhaust duct wall. The other cross fin 20 (the one that is located relatively closer to the intake duct 40 in FIG. 10 ) is connected to the cooling fins 10 extending from the intake duct wall.
As shown in FIG. 10 , a thickness t' of each cross fin 20 at its leading edge is greater than a thickness t of each cooling fin 10 at its leading edge. Note that the cooling fins 10 actually are rounded at their leading edges, as shown in FIG. 13A . In other words, each cooling fin 10 includes a curved portion 10c having a curved face and a linear portion 10d having a flat plane. In the present specification, the thickness t of each cooling fin 10 at its leading edge refers to the thickness of the outermost portion of the linear portion 10d, that is, the thickness at the boundary between the curved portion 10c and the linear portion 10d. Moreover, the cross fins 20 too are actually rounded at their leading edges, as shown in FIG. 13B . In other words, each cross fin 20 includes a curved portion 20c having a curved face and a linear portion 20d having a flat plane. In the present specification, the thickness t' of each cross fin 20 at its leading edge refers to the thickness of the outermost portion of the linear portion 20d, that is, the thickness at the boundary between the curved portion 20c and the linear portion 20d. Note that the drafts of the cooling fins 10 and the cross fins 20 are exaggerated in FIGS. 13A and 13B .
The engine (internal combustion engine) 101 of the present embodiment is a forced air-cooling type engine including the shroud 130 and the fan 121, as described above. Therefore, even when the thickness and pitch of the cooling fins 10 are reduced (i.e., the thin cooling fins 10 are placed at narrow interspaces) in order to allow as many cooling fins 10 as possible to be provided for an improved cooling efficiency, it is still possible to send sufficient cooling air CA through the gaps between adjacent cooling fins 10.
Moreover, in the forced air-cooling type engine 101 of the present embodiment, the cylinder head 100 includes the cross fins 20 which are provided so as to cross the cooling fins 10. The cross fins 20 are connected to the cooling fins 10. The thickness t' of each cross fin 20 at its leading edge is greater than the thickness t of each cooling fin 10 at its leading edge. With such cross fins 20 being provided, even if thin cooling fins 10 are provided at narrow interspaces for an improved cooling efficiency, deterioration in melt permeability at casting can be prevented, thereby preventing casting insufficiencies.
Thus, the forced air-cooling type engine 101 of the present embodiment excels in both castability and cooling efficiency of the cylinder head 100.
From the standpoint of preventing deterioration in melt permeability with greater certainty, it is preferable that the thickness t' of each cross fin 20 at its leading edge is 1.5 or more times as large as the thickness t of each cooling fin 10 at its leading edge. From the standpoint of ensuring sufficiently coolability, it is preferable that the thickness t' of each cross fin 20 at its leading edge is equal to or less than 10 times the thickness t of each cooling fin 10 at its leading edge.
The present embodiment illustrates a construction where the cylinder head 100 includes the cross fins 20; however, in addition to the cylinder head 100 (or in the place of the cylinder head 100), the cylinder block 103 may also include cross fins which are provided so as to cross the cooling fins 114 and which are connected to the cooling fins 114. Since at least one of the cylinder block 103 and the cylinder head 100 includes cross fins in addition to the cooling fins, an engine 101 which excels in both castability and cooling efficiency of the cylinder head 100 and/or the cylinder block 103 is obtained.
However, between the cylinder block 103 and the cylinder head 100, it is preferably at least the cylinder head 100 that includes the cross fins 20, as is exemplified by the present embodiment. The reason is as follows. Generally, a cylinder head is likely to have a more complicated shape than a cylinder block; therefore, if thin cooling fins are placed at narrow interspaces, melt permeability around the cooling fins is likely to be deteriorated. By providing the cross fins 20 at least on the cylinder head 100 as in the present embodiment, casting insufficiencies can be effectively prevented.
As shown in FIG. 12 , it is preferable that the cross fins 20 are at an angle of 45° or less with respect to an axis of rotation of the fan 121 (which corresponds to a center line L2 (shown for reference in FIG. 12 ) of the crankshaft 112) when viewed in the cylinder axis direction D1, as is the case with the present embodiment. When the cross fins 20 are provided at an angle of 45° or less with respect to the axis of rotation of the fan 121 as viewed in the cylinder axis direction D1 (i.e., extending more in the right-left direction than in the upper-lower direction in the case of a transverse type as in the present embodiment), the cross fins 20 are unlikely to present resistance against the cooling air CA which is sent from the fan 121. Thus, deterioration in cooling efficiency due to the provision of the cross fins 20 can be prevented.
Moreover, it is preferable that the cross fins 20 overlap with the combustion chamber 110 when viewed in the cylinder axis direction, as shown in FIG. 12 . In other words, it is preferable that the cross fins 20 are connected to the combustion chamber wall 30 defining the combustion chamber 110. When the cross fins 20 are provided in this manner, the heat generated in the combustion chamber 110 can be transmitted to the cooling fins 10 via the cross fins 20, thereby improving the cooling efficiency.
The plurality of head bolts of the engine 101 of the present embodiment include two head bolts that are located on the fan 121 side of the cylinder axis L1 (corresponding to the bolt holes 80c and 80d), such that the cross fins 20 are located in part between these two head bolts (i.e., between the bolt holes 80c and 80d), as shown in FIG. 10 and FIG. 12 . Thus placed, the cross fins 20 are close to the center of the combustion chamber 110, allowing more heat to be transmitted to the cooling fins 10 via the cross fins 20; as a result, a further enhancement in cooling efficiency is achieved.
The width w of each cross fin 20 along the cylinder axis direction D1 (see FIG. 10 ) is smaller at the leading edge 20a of the cross fin 20 (see FIG. 12 ) than at the foot 20b of the cross fin 20 (see FIG. 12 ). The width w of the cross fins 20 thus being set allows a large number of cooling fins 10 to be provided at the leading edge 20a side, while allowing at the foot 20b side the cam chamber to be placed near the combustion chamber 110, thus downsizing the cylinder head 100. In other words, both coolability and downsizing are reconciled.
Although FIG. 12 illustrates each cross fin 20 as having a constant thickness from the leading edge 20a to the foot 20b, it is preferable that the thickness of each cross fin 20 increases from the leading edge 20a toward the foot 20b. The thickness of the cross fins 20 thus being set allows more heat to be transmitted to the cooling fins 10 from the combustion chamber 110.
Although FIG. 10 illustrates the cross fins 20 as having a constant thickness along the cylinder axis direction D1, it is preferable that the thickness of each cross fin 20 increases toward the cylinder block 103 (i.e., as going in the lower direction in FIG. 10 ). The thickness of the cross fins 20 thus being set allows more heat to be transmitted to the cooling fins 10 from the combustion chamber 110.
Moreover, it is preferable that a parting line (i.e., the position at which the mold is parted in casting) P of the cylinder head 100 and/or the cylinder block 103 is somewhere between the center and the leading edge of each cooling fin 10 (or cooling fin 114) as shown in FIG. 12 , and more specifically, within 10 mm from the leading edge of each cooling fin 10 (or cooling fin 114). When the parting line P is at such a position, burrs at the parting line P are easy to remove. On the other hand, if the parting line P is somewhere between the center and the foot of each cooling fin 10 (or cooling fin 114), the deburring work will become difficult.
Preferably, the relationships t ≦ 3 and t ≦ c ≦ 3t are satisfied by the thickness t (mm) of each of the plurality of cooling fins 10 at the leading edge and the interspace c (mm) between the leading edges of any two adjacent cooling fins 10 among the plurality of cooling fins 10 (see FIG. 10 ). In other words, the thickness t is preferably 3 mm or less, and the interspace c is preferably between 1 to 3 times as much as the thickness t. By placing the thin cooling fins 10 at narrow interspaces while satisfying these relationships, it becomes possible to provide a large number of cooling fins 10, thereby improving the cooling efficiency. Note that the plurality of cooling fins 114 provided on the cylinder block 103 preferably also satisfy a similar relationship in terms of thickness at leading edges and interspace between leading edges (i.e., it is preferable that the thickness at their leading edges is 3 mm or less, and that the interspace between leading edges is between 1 to 3 times as much as the thickness at the leading edges).
Preferably, the thickness t of the cooling fins 10 at the leading edges satisfies the relationship 1 ≦ t. In other words, the thickness t of the cooling fins 10 at the leading edges is 1 mm or more. As the thickness of the cooling fins 10 decreases, more cooling fins 10 can be provided; however, if the thickness of the cooling fins 10 is too small, it will be difficult to take heat away from the cylinder head 100. This problem does not occur when the thickness t of the cooling fins 10 at the leading edges is 1 mm or more (i.e., 1 ≦ t). Similarly, the cooling fins 114 on the cylinder block 103 preferably also have a thickness of 1 mm or more at the leading edges.
Moreover, it is preferable that the interspace c between the leading edges of any two adjacent cooling fins 10 satisfies the relationship 3 ≦ c. In other words, the interspace c between the leading edges of any two adjacent cooling fins 10 is preferably 3 mm or more. When the interspace c is 3 mm or more (3 ≦ c), it is easy to supply cooling air CA to the feet of the cooling fins 10, whereby the cooling efficiency is improved. Similarly with respect to the cooling fins 114 on the cylinder block 103, it is preferable that the interspace the leading edges of any two adjacent cooling fins 114 is 3 mm or more.
Preferably, the cooling fins 10 on the cylinder head 100 and/or the cooling fins 114 on the cylinder block 103 have a draft of 2.0° or less. By ensuring that the draft is as small as 2.0° or less, it becomes possible to increase the interspace at the feet of the cooling fins 10 on the cylinder head 100 and/or the cooling fins 114 on the cylinder block 103, thereby further improving coolability. However, from the standpoint of facilitating release, it is preferable that the draft of the cooling fins 10 on the cylinder head 100 and/or the cooling fins 114 on the cylinder block 103 is 1.0° or more.
Preferably, the plurality of cooling fins 10 of the cylinder head 100 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 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 ).
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.
According to the present invention, there is provided a forced air-cooling type internal combustion engine which excels in both castability and cooling efficiency of a cylinder head and/or a cylinder block. A forced air-cooling type internal combustion engine according to the present invention provides excellent cooling efficiency, and is suitably used for various saddled vehicles such as motorcycles.
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

A forced air-cooling type internal combustion engine (101) comprising:
a cylinder block (103) molded by casting;

a cylinder head (100) molded by casting and overlaid on the cylinder block (103);

further including a cooling air duct (60);

a shroud (130) covering at least a portion of the cylinder block (103) and at least a portion of the cylinder head (100); and

a fan (121) for rotating to introduce air to an inside of the shroud (130), wherein,

at least one of the cylinder block (103) and the cylinder head (100) includes a cooling fin (10, 114) formed at least in a portion covered by the shroud (130) and a cross fin (20) provided so as to cross the cooling fin (10, 114), the cross fin (20) being connected to the cooling fin (10, 114); and

a thickness (t') of the cross fin (20) at a leading edge thereof is greater than a thickness (t) of the cooling fin (10, 114) at a leading edge thereof

characterized in that the cross fin (20) overlaps with the combustion chamber (110) when viewed in a cylinder axis (L1) direction, and which is connected to a combustion chamber wall (30); wherein the forced air-cooling type internal combustion engine further comprises a cam shaft (108) provided above a combustion chamber wall (30), and that the cooling air duct (60) is located between the cam shaft (108) and the combustion chamber wall (30).
The forced air-cooling type internal combustion engine (101) of claim 1, wherein, between the cylinder block (103) and the cylinder head (100), at least the cylinder head (100) includes the cross fin (20).
The forced air-cooling type internal combustion engine (101) of claim 1 or 2, wherein the cross fin (20) is at an angle of 45° or less with respect to an axis (L2) of rotation of the fan (121) when viewed in a cylinder axis (L1) direction.
The forced air-cooling type internal combustion engine (101) of claim 1, further comprising a plurality of head bolts (80a, 80b, 80c, 80d) for coupling the cylinder block (103) and the cylinder head (100), wherein,
the plurality of head bolts (80a, 80b, 80c, 80d) include two head bolts (80c, 80d) that are located on the fan side of a cylinder axis (L1); and
the cross fin (20) is located in part between the two head bolts (80c, 80d).
The forced air-cooling type internal combustion engine (101) of any of claims 1 to 4, wherein the width (W) of the cross fin (20) along a cylinder axis (L1) direction is smaller at the leading edge (20a) of the cross fin (20) than at a foot (20b) of the cross fin (20).
The forced air-cooling type internal combustion engine (101) of any of claims 1 to 5, wherein the thickness (t') of the cross fin (20) increases from the leading edge (20a) toward the foot (20b) of the cross fin (20).
The forced air-cooling type internal combustion engine (101) of any of claims 1 to 6, wherein the thickness (t') of the cross fin (20) increases toward the cylinder block (103).
The forced air-cooling type internal combustion engine (101) of any of claims 1 to 7, wherein a parting line (P) of at least one of the cylinder block (103) and the cylinder head (100) is located between a center of the cooling fin (10, 114) and the leading edge of the cooling fin (10, 114).
The forced air-cooling type internal combustion engine (101) of any of claims 1 to 8, wherein,
at least one of the cylinder block (103) and the cylinder head (100) includes a plurality of cooling fins (10, 114); and,
given a thickness t (mm) of each of the plurality of cooling fins (10, 114) at the leading edge and an interspace c (mm) between the leading edges of any two adjacent cooling fins (10, 114) among the plurality of cooling fins (10, 114),
the thickness t and the interspace c satisfy the relationships t≦3 and t≦c≦3t.
The forced air-cooling type internal combustion engine (101) of claim 9, wherein the thickness t further satisfies the relationship 1≦t.
The forced air-cooling type internal combustion engine (101) of claim 9 or 10, wherein the interspace c further satisfies the relationship 3≦c.
The forced air-cooling type internal combustion engine (101) of any of claims 1 to 11, wherein the cooling fin (10, 114) has a draft of not more than 1.0° and not less than 2.0°.
A saddled vehicle (1) comprising the forced air-cooling type internal combustion engine (101) of any of claims 1 to 12.