JPWO2014136535A1 - Air-cooled single-cylinder internal combustion engine, straddle-type vehicle, and air-cooled single-cylinder internal combustion engine manufacturing method - Google Patents

Abstract

The cylinder head body (100) of the air-cooled single cylinder internal combustion engine is integrally formed from an aluminum alloy by die casting, and the aluminum alloy is 8.0 wt% or more and 12.0 wt% or less of Si, 0.5 wt%. Cu, 0.002 wt% to 0.02 wt% Sr, 0.2 wt% to 0.5 wt% Mg, 0.5 wt% to 1.0 wt% Fe, and 0.3 wt% to 0. 6% by weight or less of Mn is included. The thermal conductivity at 100 ° C. of the cylinder head body (100) is 145 W / (m · K) or more, and the Rockwell hardness of the cylinder head body (100) at room temperature is 70 HRF or more and 90 HRF or less.

Description

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

  In recent years, in order to improve fuel consumption, there is an increasing demand for operating an internal combustion engine at a higher compression ratio. When the compression ratio is increased, the cylinder head is required to be excellent in high temperature strength and thermal fatigue strength.

  Patent Document 1 discloses an aluminum alloy for a cylinder head that is excellent in high cycle fatigue strength and thermal fatigue strength. In Patent Document 1, mechanical properties are improved by increasing the Cu content of the aluminum alloy. In addition, Al—Si—Cu based alloys such as AC4B are generally known as aluminum alloys having excellent high temperature strength.

  Thus, in order to improve the high temperature strength, it is considered effective to increase the Cu content of the aluminum alloy.

  On the other hand, air cooling type and water cooling type are known as cooling methods for internal combustion engines, and cylinder heads for air cooling type internal combustion engines are provided with cooling fins and cooling air passages (air holes) to ensure cooling performance. It is done. A cylinder head having a cooling air passage or the like is generally formed by low pressure casting or gravity casting using a core.

JP 2009-13480 A

  For cylinder heads for air-cooled internal combustion engines, it is conceivable to increase the Cu content of the aluminum alloy in order to improve the high temperature strength. However, in this case, although the cylinder head for the air-cooled internal combustion engine is required to have high cooling performance, the thermal conductivity decreases with an increase in the Cu content.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an air-cooled single-cylinder internal combustion engine that can be operated at a high compression ratio and has excellent fuel efficiency.

  An air-cooled single cylinder internal combustion engine according to the present invention includes a plurality of cooling fins, a cam chamber wall that defines a cam chamber, a combustion chamber wall that defines a combustion chamber, and an intake passage for performing intake to the combustion chamber. A cylinder head body having an exhaust passage for exhausting air from the combustion chamber, and a cooling air passage for passing cooling air between the cam chamber wall and the combustion chamber wall, Is integrally formed from an aluminum alloy by die casting, and the aluminum alloy is 8.0 wt% or more and 12.0 wt% or less of Si, 0.5 wt% or less of Cu, 0.002 wt% or more and 0.02 wt%. % Sr, 0.2 wt% or more and 0.5 wt% or less Mg, 0.5 wt% or more and 1.0 wt% or less Fe, and 0.3 wt% or more and 0.6 wt% or less Mn, Thermal conductivity at 100 ° C. of the head body is a 145W / (m · K) or more, Rockwell hardness at room temperature of the cylinder head body is more 70HRF 90HRF less.

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

  In one embodiment, each of the plurality of cooling fins has a draft angle of 1.0 ° to 2.0 °.

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

  In one embodiment, the plurality of cooling fins include cooling fins extending from an exhaust passage wall that defines the exhaust passage.

  In one embodiment, the cylinder head body further includes a cam chain chamber that houses a cam chain, and when viewed from the cylinder axial direction, the exhaust passage extends from the cam chain chamber toward the outlet side from the inlet side. The exhaust passage extends so that the axis of the exhaust passage is linear.

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

  In one embodiment, the plurality of cooling fins has a total area of cooling fins located on the combustion chamber side with respect to the top of the combustion chamber wall, and It is provided to be larger than the total area of the cooling fins located on the opposite side.

  In one embodiment, the plurality of cooling fins are cylinders of cooling fins located on the combustion chamber side with respect to the top of the combustion chamber wall when viewed from a side opposite to the cam chain chamber with respect to a cylinder axis. The end on the axial line side is provided so as to be located closer to the cylinder axis than the end on the cylinder axial side of the cooling fin located on the opposite side of the combustion chamber wall with respect to the top of the combustion chamber wall. Yes.

  In one embodiment, a part of the cooling air passage is an exhaust passage wall that defines the exhaust passage, and is defined by an exhaust passage wall that intersects the cam chamber wall at an acute angle.

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

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

  In one embodiment, the rib is formed along a cooling air passage wall that defines the cooling air passage.

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

  In a certain embodiment, the cross-sectional shape of the said exhaust passage along the surface orthogonal to the axis line of the said exhaust passage is a substantially ellipse, and the shape of the exit of the said exhaust passage is a substantially perfect circle.

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

  The manufacturing method of the air-cooled single cylinder internal combustion engine according to the present invention includes 8.0 wt% or more and 12.0 wt% or less of Si, 0.5 wt% or less of Cu, 0.002 wt% or more and 0.02 wt% or less of Sr, 0.002 wt% or less. A first step of preparing an aluminum alloy containing Mg of 2 wt% or more and 0.5 wt% or less, Fe of 0.5 wt% or more and 1.0 wt% or less, and Mn of 0.3 wt% or more and 0.6 wt% or less; Cooling fins, a cam chamber wall defining a cam chamber, a combustion chamber wall defining a combustion chamber, an intake passage for performing intake to the combustion chamber, and an exhaust for exhausting from the combustion chamber A second step of integrally forming a cylinder head body having a passage and a cooling air passage for passing cooling air between the cam chamber wall and the combustion chamber wall from the aluminum alloy by die casting; The second After step, water-cooling the cylinder head body includes Thereafter, a third step of performing heat treatment of the following 3 hours or more for 1 hour at 240 ° C. exceeding 260 ℃ temperature below the cylinder head body.

  In the air-cooled single-cylinder internal combustion engine according to the present invention, the cylinder head body is integrally formed from an aluminum alloy by die casting, and the aluminum alloy contains 8.0 wt% or more and 12.0 wt% or less of Si, 0.02 wt% or less. 5 wt% or less Cu, 0.002 wt% or more and 0.02 wt% or less Sr, 0.2 wt% or more and 0.5 wt% or less Mg, 0.5 wt% or more and 1.0 wt% or less Fe and 0.3 wt% or more It contains 0.6 wt% or less of Mn. By forming the cylinder head body from such an aluminum alloy, as described in (1) to (7) below, castability, cooling performance, normal temperature strength, high temperature strength, normal temperature fatigue strength, thermal cycle fatigue A cylinder head body excellent in all of strength, machinability and dimensional stability can be obtained.

  (1) Castability: Ensuring sufficient castability by setting the Si content to 8.0 wt% or more, the Mg content to 0.5 wt% or less, and the Fe content to 0.5 wt% or more. Can do. Therefore, a cylinder head body having a relatively complicated shape having cooling fins and cooling air passages (that is, a cylinder head body for an air-cooled single cylinder internal combustion engine) can be suitably formed by die casting.

  (2) Coolability: Sufficient thermal conductivity is ensured by setting the Si content to 12.0 wt% or less, the Cu content to 0.5 wt% or less, and the Sr content to 0.02 wt% or less. Cooling performance can be improved. From the viewpoint of improving the cooling performance, it is preferable to cool the cylinder head body with water after casting, and then heat-treat the cylinder head body at a temperature of 240 ° C. or higher for 1 hour or longer.

  (3) Normal temperature strength: By setting the Mg content to 0.2 wt% or more, sufficient normal temperature strength can be secured and deformation of the seating surface of the bolt boss and the cam chain chamber can be prevented. In addition, from the viewpoint of securing the normal temperature strength, the temperature and time of the heat treatment (heat treatment after casting and water cooling) to the cylinder head body are preferably 260 ° C. or less and 3 hours or less.

  (4) High temperature strength: By setting the Si content to 8.0 wt% or more and the Mg content to 0.2 wt% or more, the high temperature strength required for the cylinder head can be ensured.

  (5) Normal temperature fatigue strength: The normal temperature fatigue strength required for the cylinder head can be ensured by setting the Mg content to 0.2 wt% or more and the Mn content to 1/2 or more of the Fe content.

  (6) Thermal cycle fatigue strength: Si content is 12.0 wt% or less, Sr content is 0.002 wt% or more, Fe content is 1.0 wt% or less, and Mn content is 0.3 wt% or more. By doing so, it is possible to ensure sufficient thermal fatigue strength and to operate at a high compression ratio.

  (7) Machinability and dimensional stability: By setting the Si content to 12.0 wt% or less and the Mn content to 0.6 wt% or less, it is sufficient for a thick portion such as a combustion chamber wall. Machinability and dimensional stability can be ensured, and port processing after casting can be performed to improve the performance of the internal combustion engine. From the viewpoint of ensuring dimensional stability, the temperature and time of the heat treatment (heat treatment after casting and water cooling) to the cylinder head body are preferably 240 ° C. or more and 1 hour or more.

  In the air-cooled single cylinder internal combustion engine according to the present invention, the thermal conductivity of the cylinder head body at 100 ° C. is 145 W / (m · K) or more. When the thermal conductivity of the cylinder head body at 100 ° C. is 145 W / (m · K) or more, the cooling performance of the cylinder head body can be sufficiently improved.

  Furthermore, in the air-cooled single-cylinder internal combustion engine according to the present invention, the Rockwell hardness of the cylinder head body at normal temperature is not less than 70 HRF and not more than 90 HRF. When the Rockwell hardness of the cylinder head body at normal temperature is less than 70 HRF, the strength required for the cylinder head body may not be ensured. Further, when the Rockwell hardness of the cylinder head body at room temperature exceeds 90 HRF, the intermetallic compound is finely precipitated at a high density, and a desired thermal conductivity cannot be obtained.

  Thus, according to the present invention, a cylinder head body excellent in all of castability, cooling performance, normal temperature strength, high temperature strength, normal temperature fatigue strength, thermal cycle fatigue strength, machining workability and dimensional workability can be obtained. Therefore, an air-cooled single cylinder internal combustion engine that can be operated at a high compression ratio and has excellent fuel efficiency can be realized.

  In the air-cooled single-cylinder internal combustion engine according to the present invention, the cylinder head body is formed by die casting, so that the thickness and pitch of the cooling fins can be reduced, and the cooling performance can be improved. Specifically, the thickness of the tip of each cooling fin is 1.0 mm to 2.5 mm, and a plurality of cooling fins can be arranged at a pitch of 7.5 mm or less, which improves the cooling performance. Can be made.

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

  If the exhaust passage is formed by a mold without using the core, the surface roughness of the inner peripheral surface of the exhaust passage can be reduced as compared with the case where the core is used. More specifically, the surface roughness Rz (maximum height) of the inner peripheral surface of the exhaust passage can be made 30 μm or less, and the exhaust resistance can be reduced to improve the output of the internal combustion engine.

  Typically, the plurality of cooling fins include cooling fins extending from an exhaust passage wall defining an exhaust passage. Since the exhaust passage is a portion that is likely to be hot in the cylinder head body, the cooling efficiency can be improved by extending the cooling fin from the exhaust passage wall.

  If the exhaust passage of the cylinder head main body extends away from the cam chain chamber as it goes from the inlet side to the outlet side, the space between the outlet of the exhaust passage and the cam chain chamber can be expanded. Therefore, it is easy to ensure a sufficiently large cross-sectional area of the cooling air passage. Therefore, higher cooling performance can be realized. Further, if the exhaust passage of the cylinder head body is formed so that the axis thereof is linear, the exhaust resistance is reduced and more efficient combustion is possible. Furthermore, when the cylinder head body is formed by die casting, the final exhaust passage can be formed by a mold, so that it is not necessary to finish or change the shape of the exhaust passage by post-processing.

  If the bolt hole into which the head bolt is inserted is provided between the exhaust passage and the cam chain chamber, the space is narrower than that between the exhaust passage and the cam chain chamber (that is, between the bolt hole and the exhaust passage). It is necessary to position (arrange) a part of the cooling air passage in the space. However, as described above, the exhaust passage extends away from the cam chain chamber from the inlet side toward the outlet side, so that the cross-sectional area of the cooling air passage is sufficient between the bolt hole and the exhaust passage. It can be secured greatly.

  In the plurality of cooling fins, the total area of the cooling fins located on the combustion chamber side with respect to the top of the combustion chamber wall is equal to the area of the cooling fins located on the opposite side of the combustion chamber with respect to the top of the combustion chamber wall. It is preferable to be provided so as to be larger than the total. During operation of the internal combustion engine, in the cylinder head body, the region on the combustion chamber side with respect to the top of the combustion chamber wall has a higher temperature than the region on the side opposite to the combustion chamber with respect to the top of the combustion chamber wall. Become. Therefore, since the total area of the cooling fins located in the former area is larger than the total area of the cooling fins located in the latter area, the cooling performance can be improved efficiently.

  Further, when viewed from the side opposite to the cam chain chamber with respect to the cylinder axis, the plurality of cooling fins have ends on the cylinder axis side of the cooling fins positioned on the combustion chamber side with respect to the top of the combustion chamber wall. It is preferable that the cooling fin located on the opposite side of the combustion chamber wall with respect to the top of the combustion chamber wall is located closer to the cylinder axis than the end on the cylinder axis side. The end of the cooling fin located on the combustion chamber side relative to the top of the combustion chamber wall is on the cylinder axis side of the cooling fin located on the opposite side of the combustion chamber from the top of the combustion chamber wall By positioning the end of the latter cooling fin away from the cylinder axis rather than the end of the former cooling fin, the cross-sectional area of the cooling air passage is further increased. Can be bigger.

  If a part of the cooling air passage is an exhaust passage wall that defines the exhaust passage and is defined by the exhaust passage wall that intersects the cam chamber wall at an acute angle, the following advantages are obtained. Normally, when the shape of the cooling air passage is formed by a die during die casting, the portion of the die corresponding to the cooling air passage has a shape protruding from the other portion. The tip of the portion having such a protruding shape is likely to become high temperature due to the heat of the molten metal. In particular, if there is a corner at the tip, the part of the mold may be melted. Therefore, in general, the tip is designed to have a circular cross section, but by defining a part of the cooling air passage with an exhaust passage wall that intersects with the cam chamber wall at an acute angle, The cross-sectional area of the cooling air passage can be increased. In this case, since both the cam chamber wall and the exhaust passage wall may be small in thickness, the problem of melting damage can be avoided.

  The cam chamber wall preferably has a thickness of 2.5 mm or less. When the thickness of the cam chamber wall is 2.5 mm or less, the mold corner can be more reliably prevented from being melted. However, if the cam chamber wall thickness is less than 1.5 mm, the sufficient pressure resistance required for the cam chamber cannot be obtained, and the resistance to deformation stress caused by strain may be insufficient. The wall thickness is preferably 1.5 mm or more.

  The cylinder head body preferably further includes a rib provided in the cooling air passage and connecting the combustion chamber wall and the cam chamber wall. Since the rib connects the combustion chamber wall and the cam chamber wall, the rib transmits heat from the combustion chamber wall to the cam chamber wall, and cooling using the lubricating oil in the cam chamber is possible, improving cooling performance. Can be made. Moreover, the cooling effect by a cooling wind is also acquired by arrange | positioning a rib in a cooling wind channel | path.

  In addition, it is preferable that the rib is formed along a die cutting direction when the cylinder head body is formed by die casting. Therefore, it is preferable that the rib is formed along a wall portion (cooling air passage wall) that defines the cooling air passage.

  Further, it is preferable that the cross-sectional shape of the exhaust passage along a plane orthogonal to the axis of the exhaust passage is substantially elliptical, and the shape of the outlet of the exhaust passage is substantially perfect circle. Since the cross-sectional shape of the exhaust pipe is generally a perfect circle, the shape of the exit of the exhaust passage is a substantially perfect circle, thereby preventing a rapid change in the passage area and preventing a decrease in the performance of the internal combustion engine. it can. When the exhaust passage extends away from the cam chain chamber as it goes from the inlet side to the outlet side, the shape of the outlet of the exhaust passage is such that the cross-sectional shape of the exhaust passage along the plane orthogonal to the axis is substantially a circle. Cannot be made into a perfect circle. In contrast, when the cross-sectional shape of the exhaust passage along the plane orthogonal to the axis is substantially oval, that is, the roundness of the cross-sectional shape of the exhaust passage along the plane orthogonal to the axis is determined by the outlet of the exhaust passage. By making it lower than the roundness of the shape, the shape of the outlet of the exhaust passage can be made substantially circular.

  In the method for manufacturing an air-cooled single cylinder internal combustion engine according to the present invention, in the first step, 8.0 wt% or more and 12.0 wt% or less of Si, 0.5 wt% or less of Cu, 0.002 wt% or more and 0.02 wt% or less. An aluminum alloy containing the following Sr, 0.2 wt% to 0.5 wt% Mg, 0.5 wt% to 1.0 wt% Fe and 0.3 wt% to 0.6 wt% Mn is prepared, In the second step, the cylinder head body is integrally formed from this aluminum alloy by die casting. Therefore, all of castability, cooling property, normal temperature strength, high temperature strength, normal temperature fatigue strength, thermal cycle fatigue strength, machinability and dimensional stability for the same reasons as described in (1) to (7) above. A cylinder head body excellent in performance can be obtained. In the method for manufacturing an air-cooled single cylinder internal combustion engine according to the present invention, the cylinder head body is water-cooled after the second step, and then the cylinder head body is heated at a temperature of 240 ° C. to 260 ° C. for 1 hour to 3 hours. A third step of performing the following heat treatment is performed. When the heat treatment temperature is 240 ° C. or higher and the heat treatment time is 1 hour or longer, the effect of ensuring sufficient thermal conductivity and improving the cooling property can be obtained more reliably. Further, when the heat treatment temperature is 260 ° C. or less and the heat treatment time is 3 hours or less, the dimensional stability required for the cylinder head body can be ensured. For the above reasons, according to the manufacturing method of the present invention, an air-cooled single-cylinder internal combustion engine that can be operated at a high compression ratio and has excellent fuel efficiency can be preferably manufactured.

  According to the present invention, an air-cooled single-cylinder internal combustion engine that can be operated at a high compression ratio and has excellent fuel efficiency is provided.

1 is a right side view schematically showing a motorcycle (saddle-type vehicle) 1 in an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line 2A-2A ′ in FIG. 1. FIG. 3 is an enlarged view showing the vicinity of an engine (internal combustion engine) 101 shown in FIG. 2. 2 is a right side view of a part of the engine 101. FIG. 2 is a left side sectional view of the engine 101. FIG. It is a top view which shows typically the cylinder head main body 100 with which the engine 101 in embodiment of this invention is provided. It is a bottom view showing typically cylinder head body 100 with which engine 101 in an embodiment of the present invention is provided. It is a front view showing typically cylinder head body 100 with which engine 101 in an embodiment of the present invention is provided. It is a rear view showing typically cylinder head body 100 with which engine 101 in an embodiment of the present invention is provided. It is a left view which shows typically the cylinder head main body 100 with which the engine 101 in embodiment of this invention is provided. It is a right view which shows typically the cylinder head main body 100 with which the engine 101 in embodiment of this invention is provided. It is a figure which shows typically the cylinder head main body 100 with which the engine 101 in embodiment of this invention is provided, and is sectional drawing along line 12A-12A 'in FIG. It is a figure which shows typically the cylinder head main body 100 with which the engine 101 in embodiment of this invention is provided, and is sectional drawing along the 13A-13A 'line in FIG. It is a figure which shows typically the several cooling fin 10 which the cylinder head main body 100 has.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment.

  FIG. 1 shows a straddle-type vehicle 1 according to this embodiment. A straddle-type vehicle 1 shown in FIG. 1 is a scooter type motorcycle. The straddle type vehicle according to the present invention is not limited to the scooter type motorcycle 1. The saddle riding type vehicle according to the present invention may be a so-called moped type, off-road type, on-road type or other type of motorcycle. Further, the saddle riding type vehicle according to the present invention means an arbitrary vehicle on which an occupant rides and is not limited to a two-wheeled vehicle. The straddle-type vehicle according to the present invention may be a tricycle or the like that changes the traveling direction by tilting the vehicle body, or may be another straddle-type vehicle such as an ATV (All Terrain Vehicle).

  In the following description, front, rear, left, and right mean front, rear, left, and right, respectively, as viewed from the occupant of the motorcycle 1. Reference numerals F, Re, L, and R in the figure represent front, rear, left, and right, respectively.

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

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

  As shown in FIG. 2, the engine unit 5 includes an engine (internal combustion engine) 101 and a V-belt continuously variable transmission (hereinafter referred to as “CVT”) 150. In the example shown in FIG. 2, the engine 101 and the CVT 150 are integrated to form the engine unit 5, but it is needless to say that the engine 101 and the transmission may be separate.

  The engine 101 is a single cylinder engine having a single cylinder. The engine 101 is a four-stroke engine that sequentially repeats an intake process, a compression process, a combustion process, and an exhaust process. The engine 101 has a crankcase 102 and a front side from the crankcase 102 (note that “front” here is not limited to the front in a strict sense, that is, a direction parallel to the horizontal line, and includes a direction inclined from the horizontal line. A cylinder block 103 coupled to the crankcase 102, a cylinder head 104 connected to the front portion of the cylinder block 103, and a cylinder head cover 105 connected to the front portion of the cylinder head 104. . A cylinder 106 is formed inside the cylinder block 103.

  The cylinder 106 may be formed by a cylinder liner or the like inserted into the main body of the cylinder block 103 (that is, a portion of the cylinder block 103 other than the cylinder 106), and is integrated with the main body of the cylinder block 103. May be. In other words, the cylinder 106 may be formed so as to be separable from the main body of the cylinder block 103, or may be formed so as not to be separable 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 freely reciprocate between the top dead center TDC and the bottom dead center BDC.

  The cylinder head 104 is overlaid on the cylinder block 103 so as to cover the cylinder 106. The cylinder head 104 includes an aluminum alloy cylinder head body 100, a valve mechanism including a camshaft 108, an intake valve 151, an exhaust valve 152, and the like. The valve mechanism is accommodated in the cam chamber 109. A portion 20 of the cylinder head body 100 that defines the cam chamber 109 is referred to as a cam chamber wall as will be described later.

  Combustion chamber 110 is defined by cylinder head body 100, the top surface of piston 107, and the inner peripheral surface of cylinder 106. A portion 30 defining the combustion chamber 110 of the main body of the cylinder head 100 is referred to as a combustion chamber wall as will be described later.

  The piston 107 is connected to the crankshaft 112 via a connecting rod 111. The crankshaft 112 extends to the left and right and is supported by the crankcase 102. The camshaft 108 is driven by the cam chain 113 connected to the crankshaft 112. The cam chain 113 is accommodated in the cam chain chamber 70.

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

  As shown in FIG. 2, the CVT 150 includes a first pulley 161 that is a driving pulley, a second pulley 162 that is a driven pulley, and a V belt wound around the first pulley 161 and the second pulley 162. 153. The left end portion of the crankshaft 112 protrudes leftward from the crankcase 102. The first pulley 161 is attached to the left end portion of the crankshaft 112. The second pulley 162 is attached to the main shaft 154. The main shaft 154 is connected to the rear wheel shaft 155 via a gear mechanism (not shown). A transmission case 156 is provided on the left side of the crankcase 102. CVT 150 is accommodated in transmission case 156.

  A generator 120 is provided on the right side portion of the crankshaft 112. A cooling fan 121 is fixed to the right end portion of the crankshaft 112. The cooling fan 121 rotates together with the crankshaft 112. The cooling fan 121 is formed to suck air to the left by rotating. A shroud 130 is provided in the crankcase 102, the cylinder block 103, and the cylinder head 104. The generator 120 and the cooling fan 121 are accommodated in the shroud 130.

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

  An intake pipe 141 is connected to the upper portion of the cylinder head 104. An exhaust pipe 142 is connected to the lower part of the cylinder head 104. An intake passage 40 and an exhaust passage 50 are formed inside the cylinder head 104. The intake pipe 141 is connected to the intake passage 40, and the exhaust pipe 142 is connected to the exhaust passage 50. An intake valve 151 and an exhaust valve 152 are provided in the intake passage 40 and the exhaust passage 50, respectively.

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

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

  The inner member 131 has a hole 131a into which an ignition device 115 such as a spark plug is inserted. A suction port 132 a is formed in the outer member 132. When the shroud 130 is attached to the engine unit 5, the suction port 132a is disposed at a position facing the cooling fan 121 (see FIG. 3). 4 represents the outer periphery of the cooling fan 121, and reference numeral B represents the rotation direction of the cooling fan 121.

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

  When the cooling fan 121 rotates with the rotation of the crankshaft 112, the air outside the shroud 130 is introduced into the shroud 130 through the suction port 132a. The air introduced into the shroud 130 is blown to the cylinder block 103 and the cylinder head 104. The cylinder block 103 and the cylinder head 104 are cooled by this air.

  Next, the configuration of the cylinder head body 100 included in the engine 101 according to the present embodiment will be specifically described with reference to FIGS. 6 and 7 are a top view and a bottom view schematically showing the cylinder head body 100. FIG. 8 and 9 are a front view and a rear view schematically showing the cylinder head body 100. FIG. 10 and 11 are a left side view and a right side view schematically showing the cylinder head main body 100. 12 is a cross-sectional view taken along the line 12A-12A 'in FIG. 11, and FIG. 13 is a cross-sectional view taken along the line 13A-13A' in FIG. In some drawings, the cylinder axis direction is indicated by an arrow D1. Needless to say, the cylinder axis direction is a direction parallel to the cylinder axis L1. In the following description, the side where the connection to the intake pipe 141 is performed is described as the front side of the cylinder head body 100.

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

  As shown in FIGS. 8, 9, and 10, the plurality of cooling fins 10 are provided on the outer side surface (more specifically, the left side surface) of the cylinder head body 100, and face the outside of the cylinder head body 100. (Ie, extending in a direction substantially perpendicular to the cylinder axis direction D1). The plurality of cooling fins 10 are arranged at a predetermined pitch along the cylinder axial direction D1. The number of cooling fins 10 is not limited to that exemplified here.

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

  Combustion chamber wall 30 (shown in FIGS. 7 and 13) defines combustion chamber 110. The combustion chamber 110 is a space formed by the combustion chamber wall 30 of the cylinder head body 100, the top surface of the piston 107, and the inner peripheral surface of the cylinder 106. As shown in FIG. 7, a plug hole 32 is formed in the combustion chamber wall 30 in addition to an intake port 40a and an exhaust port 50a described later. A spark plug of the ignition device 115 is attached to the plug hole 32.

  The intake passage 40 is a passage for performing intake to the combustion chamber 110. An opening 40a on the combustion chamber wall 30 side of the intake passage 40 is an intake port. As the intake valve 151 moves up and down by the valve mechanism, the intake port 40a is opened and closed. An intake pipe 141 is connected to an opening 40 b (located in front of the cylinder head main body 100) on the opposite side of the intake passage 40 from the combustion chamber wall 30.

  The exhaust passage 50 is a passage for exhausting from the combustion chamber 110. An opening 50a on the combustion chamber wall 30 side of the exhaust passage 50 is an exhaust port. When the exhaust valve 152 moves up and down by the valve operating mechanism, the exhaust port 50a is opened and closed. An exhaust pipe 142 is connected to the opening 50 b on the opposite side of the exhaust passage 50 from the combustion chamber wall 30.

  Typically, the plurality of cooling fins 10 includes a cooling fin 10 (relatively located on the right side in FIG. 10) that extends from an exhaust passage wall that defines the exhaust passage 50. In the present embodiment, the plurality of cooling fins 10 further includes a cooling fin 10 (located relatively on the left side in FIG. 10) extending from the intake passage wall that defines the intake passage 40.

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

  The cylinder head body 100 is integrally formed from an aluminum alloy by die casting. The aluminum alloy that is the material of the cylinder head body 100 is 8.0 wt% or more and 12.0 wt% or less of Si (silicon), 0.5 wt% or less of Cu (copper), 0.002 wt% or more and 0.02 wt% or less. Sr (strontium), 0.2 wt% to 0.5 wt% Mg (magnesium), 0.5 wt% to 1.0 wt% Fe (iron), and 0.3 wt% to 0.6 wt% Mn ( Manganese).

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

  The exhaust passage 50 is a cam chain as viewed from the cylinder axial direction D1 (direction perpendicular to the paper surface in FIGS. 6, 7 and 12) from the inlet (exhaust port 50a) side to the outlet (opening 50b) side. It extends away from the chamber 70. That is, the axis 50x of the exhaust passage 50 is inclined with respect to the front-rear direction of the cylinder head body 100. Further, the exhaust passage 50 is formed such that its axis 50x is linear when viewed from the cylinder axis direction D1.

  Further, as shown in FIGS. 6, 7 and 12, the cylinder head body 100 has a plurality of bolt holes 80a to 80d through which head bolts are inserted. The cylinder head main body 100 is coupled to the cylinder block 103 by head bolts (typically stud bolts) inserted through these bolt holes 80a to 80d. One bolt hole (a bolt hole located at the upper right in FIGS. 6 and 12 and located at the lower right in FIG. 7) 80a of the plurality (four in this case) of bolt holes 80a to 80d is connected to the exhaust passage 50. It is provided between the cam chain chamber 70. A part of the cooling air passage 60 is located between the bolt hole 80 a and the exhaust passage 50. The boss 80 having the bolt holes 80a to 80d may be called a head bolt boss or a stud bolt boss.

  As already described, in the engine 101 in the present embodiment, the cylinder head body 100 is integrally formed from an aluminum alloy by die casting, and the aluminum alloy is 8.0 wt% or more and 12.0 wt% or less. Si, 0% to 0.5wt% Cu, 0.002wt% to 0.02wt% Sr, 0.2wt% to 0.5wt% Mg, 0.5wt% to 1.0wt% Fe and Mn of 0.3 wt% or more and 0.6 wt% or less are included. Since the cylinder head body 100 is formed of such an aluminum alloy, as described in the following (1) to (7), castability, cooling performance, normal temperature strength, high temperature strength, normal temperature fatigue strength, thermal cycle The cylinder head body 100 excellent in all of fatigue strength, machinability and dimensional stability can be obtained.

  (1) Castability: The fluidity of the molten metal can be ensured by setting the Si content to 8.0 wt% or more and the Mg content to 0.5 wt% or less. Moreover, the seizing to a metal mold | die can be prevented by making Fe content into 0.5 wt% or more. Therefore, sufficient castability can be ensured by setting the Si content to 8.0 wt% or more, the Mg content to 0.5 wt% or less, and the Fe content to 0.5 wt% or more. Therefore, a cylinder head body having a relatively complicated shape having cooling fins and cooling air passages (that is, a cylinder head body for an air-cooled single cylinder internal combustion engine) can be suitably formed by die casting.

  (2) Coolability: Sufficient thermal conductivity is ensured by setting the Si content to 12.0 wt% or less, the Cu content to 0.5 wt% or less, and the Sr content to 0.02 wt% or less. Cooling performance can be improved. From the viewpoint of improving the cooling performance, it is preferable to cool the cylinder head body with water after casting, and then heat-treat the cylinder head body at a temperature of 240 ° C. or higher for 1 hour or longer.

  (3) Normal temperature strength: The alloy can be precipitation strengthened by setting the Mg content to 0.2 wt% or more. Therefore, sufficient room temperature strength can be secured and deformation of the bearing surface of the bolt boss and the cam chain chamber can be prevented. In addition, from the viewpoint of securing the normal temperature strength, the temperature and time of the heat treatment (heat treatment after casting and water cooling) to the cylinder head body are preferably 260 ° C. or less and 3 hours or less.

  (4) High temperature strength: Dispersion strengthening of the alloy can be achieved by setting the Si content to 8.0 wt% or more. In addition, the alloy can be precipitation strengthened by setting the Mg content to 0.2 wt% or more. Therefore, by setting the Si content to 8.0 wt% or more and the Mg content to 0.2 wt% or more, the high temperature strength required for the cylinder head can be ensured.

  (5) Normal temperature fatigue strength: The alloy can be precipitation strengthened by setting the Mg content to 0.2 wt% or more. Further, when the Mn content is at least 1/2 of the Fe content, generation of coarse Fe needle-like precipitates can be suppressed. Therefore, normal temperature fatigue strength required for the cylinder head can be secured by setting the Mg content to 0.2 wt% or more and the Mn content to 1/2 or more of the Fe content.

  (6) Thermal cycle fatigue strength: Toughness can be increased by setting the Si content to 12.0 wt% or less. Moreover, Si can be finely dispersed by making Sr content 0.002 wt% or more. Furthermore, the amount of intermetallic compounds can be regulated by setting the Fe content to 1.0 wt% or less. Moreover, generation | occurrence | production of the coarse Fe needle-like precipitate can be suppressed by making Mn content 0.3 wt% or more. Therefore, by setting the Si content to 12.0 wt% or less, the Sr content to 0.002 wt% or more, the Fe content to 1.0 wt% or less, and the Mn content to 0.3 wt% or more, sufficient It becomes possible to ensure the thermal fatigue strength and to operate at a high compression ratio.

  (7) Machinability and dimensional stability: Combustion by regulating the amount and size of precipitates by setting the Si content to 12.0 wt% or less and the Mn content to 0.6 wt% or less Sufficient machinability and dimensional stability can be secured even for a thick portion such as a chamber wall, and port processing after casting can be performed to improve the performance of the internal combustion engine. From the viewpoint of ensuring dimensional stability, the temperature and time of the heat treatment (heat treatment after casting and water cooling) to the cylinder head body are preferably 240 ° C. or more and 1 hour or more.

  Further, in the engine 101 in the present embodiment, the thermal conductivity at 100 ° C. of the cylinder head body 100 is 145 W / (m · K) or more. When the thermal conductivity at 100 ° C. of the cylinder head body 100 is 145 W / (m · K) or more, the cooling performance of the cylinder head body 100 can be sufficiently improved.

  Furthermore, in the engine 101 in this embodiment, the Rockwell hardness of the cylinder head body 100 at normal temperature is preferably 70 HRF or more and 90 HRF or less. When the Rockwell hardness at normal temperature of the cylinder head main body 100 is less than 70 HRF, the cylinder head main body 100 may not have a required strength. Further, when the Rockwell hardness at normal temperature of the cylinder head body 100 exceeds 90 HRF, the intermetallic compound is finely precipitated at a high density, and a desired thermal conductivity cannot be obtained.

  As described above, according to the present invention, the cylinder head body 100 excellent in all of castability, cooling performance, normal temperature strength, high temperature strength, normal temperature fatigue strength, thermal cycle fatigue strength, machinability and dimensional stability can be obtained. Therefore, an engine (air-cooled single-cylinder internal combustion engine) 101 that can be operated at a high compression ratio and has excellent fuel efficiency can be realized.

  The engine 101 in the present embodiment can be manufactured as follows, for example.

  First, 8.0 wt% or more and 12.0 wt% or less of Si, 0.5 wt% or less of Cu, 0.002 wt% or more of 0.02 wt% or less of Sr, 0.2 wt% or more of 0.5 wt% or less of Mg, 0 An aluminum alloy containing Fe of 5 wt% to 1.0 wt% and Mn of 0.3 wt% to 0.6 wt% is prepared. As long as it is within the above range, the composition of the aluminum alloy is not limited.

  Next, the cylinder head body 100 having the plurality of cooling fins 10, the cam chamber wall 20, the combustion chamber wall 30, the intake passage 40, the exhaust passage 50, and the cooling air passage 60 is integrally formed by die casting from the above aluminum alloy. Mold. After molding, the cylinder head body 100 is water-cooled, and then the cylinder head body 100 is subjected to heat treatment (T5 overaging treatment) at a temperature of 240 ° C. or higher and 260 ° C. or lower for 1 hour or longer and 3 hours or shorter.

  Subsequently, necessary machining is performed on the cylinder head body 100. In this way, the cylinder head body 100 is obtained.

  Separately from the production of the cylinder head main body 100 as described above, a crankcase 102, a cylinder block 103, and the like are prepared. Then, the engine 101 is assembled using the cylinder head body 100, the crankcase 102, the cylinder block 103, and the like. In this way, the engine 101 is completed.

  In the manufacturing method described above, after the step of forming the cylinder head body 100, the cylinder head body 100 is water-cooled, and then the cylinder head body 100 is subjected to heat treatment at a temperature of 240 ° C. to 260 ° C. for 1 hour to 3 hours. The process of performing is performed. When the heat treatment temperature is 240 ° C. or higher and the heat treatment time is 1 hour or longer, the effect of ensuring sufficient thermal conductivity and improving the cooling property can be obtained more reliably. Further, when the heat treatment temperature is 260 ° C. or less and the heat treatment time is 3 hours or less, the dimensional stability required for the cylinder head body 100 can be ensured.

  Here, the cylinder head main body 100 (Examples 1 and 2) manufactured under the above-described heat treatment conditions using an aluminum alloy whose Si, Cu, Sr, Mg, Fe, and Mn contents are all in the above-described range, Made of aluminum alloy with at least one of Si, Cu, Sr, Mg, Fe and Mn content outside the above range, or heat treated outside the above time range and / or temperature range The results of evaluating the characteristics of the cylinder head body (Comparative Examples 1 to 33) will be described.

  Tables 1, 2 and 3 below show the composition of the aluminum alloy, the heat treatment temperature (aging temperature), and the heat treatment time for Examples 1 and 2 and Comparative Examples 1 to 33. In Tables 2 and 3, the numerical values of the components of the aluminum alloys of Comparative Examples 1 to 33 that are outside the above range are shown in italics. Moreover, the numerical values of the heat treatment temperatures and heat treatment times of Comparative Examples 1 to 33 that are outside the above-described range are shown in italics.

Tables 4, 5 and 6 show the castability, thermal conductivity, room temperature strength, high temperature strength, room temperature fatigue strength, thermal cycle fatigue strength, and machinability for Examples 1 and 2 and Comparative Examples 1 to 33. And the result of having evaluated dimensional stability is shown. As for the castability evaluation results, the case where no hot water failure or seizure to the mold did not occur was indicated as “◯”, and the case where it occurred was indicated as “X”. Regarding the evaluation result of thermal conductivity, the case where the thermal conductivity at 100 ° C. is 145 W / (m · K) or more is “◯”, and the case where it is less than 145 W / (m · K) is “x”. . Regarding the evaluation result of the strength at normal temperature (room temperature strength), the case where the tensile strength is 180 MPa or more is “◯”, and the case where the tensile strength is less than 180 MPa is “×”. Regarding the strength at 175 ° C. (high temperature strength), the case where the 0.2% proof stress is 120 MPa or more is “◯”, and the case where it is less than 120 MPa is “X”. Regarding the normal temperature fatigue strength, the case where the 10 ⁷ times fatigue strength is 100 MPa or more is “◯”, and the case where the fatigue strength is less than 100 MPa is “×”. Regarding the thermal cycle fatigue strength, the case where the allowable strain amount that does not break at a normal temperature and 250 ° C. in 500 cycles is 0.4% or more is “◯”, and the case where it is less than 0.4% is “×”. Yes. As for the evaluation result of machinability, “X” was given when there was a case where the life of the cutting tool was reduced due to chipping of the cutting edge, and “◯” was given otherwise. Regarding dimensional stability, “◯” indicates a small dimensional change after machining due to heat generated by engine operation, and “×” indicates a large dimensional stability.

  The heat treatment temperature affects the thermal conductivity, normal temperature strength, and dimensional stability. When the heat treatment temperature is higher than 260 ° C., aging progresses even in a short time and becomes over-aged, and the material is softened. Therefore, the thermal conductivity increases and the normal temperature strength decreases. Normal temperature fatigue strength correlates with normal temperature strength, and those with low normal temperature strength also have low normal temperature fatigue strength. Further, if the heat treatment temperature is lower than 240 ° C., a dimensional change occurs when heat that is higher than the heat treatment temperature is applied by engine operation. Further, even if the heat treatment temperature is 260 ° C. or lower and 240 ° C. or higher, if heat treatment is performed for 3 hours or longer, the aging similarly proceeds and the material becomes soft due to overaging. Moreover, since a thick part exists in a part in the cylinder head, if the heat treatment time is 1 hour or less, a part of the product is in a state where the heat treatment is not completed. When the material softens due to the above-described causes, a Rockwell hardness of 70 HRF or more may not be realized at room temperature. Further, if the heat treatment temperature is less than 240 ° C. or the heat treatment time is less than 1 hour, a thermal conductivity of 145 W / (m · K) or more may not be realized.

  As can be seen from Tables 1 to 6, in Examples 1 and 2, “◯” is indicated for all evaluation items, and there is no evaluation item indicated by “×”. On the other hand, in Comparative Examples 1 to 33, “x” is shown for at least one evaluation item. Hereinafter, the reason why a favorable result was not obtained in the comparative example (that is, the reason why a good result was obtained in the example) will be described for each evaluation item.

  As for castability, good evaluation results were not obtained in Comparative Examples 1, 4, 6, 8, 9, 11, 13, 15, 17, 20, 27, and 29. This is because the Si content is less than 8.0 wt% (Comparative Examples 1, 6, 8, 12, 13, 17 and 29), and the Fe content is less than 0.5 wt% (Comparative Example 1, 4, 9, 11, 15, 17 and 27) or the Mg content exceeds 0.5 wt% (Comparative Examples 8, 9, 17 and 20). If the Si content is less than 8.0 wt%, poor hot water may occur, which may cause casting defects. On the other hand, if the Mg content exceeds 0.5 wt%, the viscosity of the molten metal increases and a hot water defect may occur, which may cause casting defects. Further, if the Fe content is less than 0.5 wt%, seizure to the mold may occur.

  On the other hand, in Examples 1 and 2 in which the Si content is 8.0 wt% or more, the Mg content is 0.5 wt% or less, and the Fe content is 0.5 wt% or more, poor hot water does not occur. Neither did seizure to the mold occur. Thus, sufficient castability is ensured by setting the Si content of the aluminum alloy to 8.0 wt% or more, the Mg content to 0.5 wt% or less, and the Fe content to 0.5 wt% or more. Confirmed to get.

  Regarding thermal conductivity, good results were not obtained in Comparative Examples 1 to 11, 15, 16, 18, 19, 21, 24, 32, and 33. This is considered to be mainly caused by the Cu content exceeding 0.5 wt% (Comparative Examples 1 to 9 and 19). This is because addition of Cu to the aluminum alloy improves the normal temperature and high temperature strength but decreases the thermal conductivity.

  However, in Comparative Examples 10, 11, 15, 16, 18, 21, and 24, good results were not obtained even though the Cu content was 0.5 wt% or less. This is because the Si content exceeds 12.0 wt% (Comparative Examples 11, 15, 16 and 24) or the Sr content exceeds 0.02 wt% (Comparative Example 21). It is thought that. The reason why sufficient thermal conductivity cannot be obtained when the Si content exceeds 12.0 wt% is that heat conduction is hindered by the precipitation of Si in the α phase and the division of the α phase. . The reason why the sufficient thermal conductivity cannot be obtained when the Sr content exceeds 0.02 wt% is that Si is finely dispersed in the crystal grain boundaries and heat conduction is hindered. Alternatively, the heat treatment temperature is less than 240 ° C. and the heat treatment time is less than 1 hour (Comparative Examples 10, 18, 32 and 33).

  In contrast, the Si content is 12.0 wt% or less, the Cu content is 0.5 wt% or less, the Sr content is 0.02 wt% or less, the heat treatment temperature is 240 ° C. or more, and the heat treatment time is 1 hour or more. In Examples 1 and 2, the thermal conductivity at 100 ° C. was 145 W / (m · K) or more. Thus, the Si content is 12.0 wt% or less, the Cu content is 0.5 wt% or less, the Sr content is 0.02 wt% or less, the heat treatment temperature is 240 ° C. or more, and the heat treatment time is 1 hour or more. By doing this, it was confirmed that sufficient heat conductivity could be secured and the cooling performance could be improved.

Regarding the room temperature strength, good results were not obtained in Comparative Examples 3, 4, 7, 10-13, 17, 25, 30 and 31. This is mainly due to the Mg content being less than 0.2 wt% (Comparative Examples 10-12 and 25). If the Mg content is less than 0.2 wt%, the effect of improving the strength due to precipitation of Mg ₂ Si may not be sufficiently obtained. Further, the heat treatment temperature is higher than 260 ° C. (Comparative Examples 3, 4, 13, and 30) and the heat treatment time is longer than 3 hours (Comparative Examples 3, 4, 7, 17, and 31).

  On the other hand, in Examples 1 and 2 in which the Mg content was 0.2 wt% or more, the heat treatment temperature was 260 ° C. or less, and the heat treatment time was 3 hours or less, the normal temperature strength was 180 MPa or more. Thus, it was confirmed that sufficient room temperature strength could be secured by setting the Mg content to 0.2 wt% or more, the heat treatment temperature to 260 ° C. or less, and the heat treatment time to 3 hours or less.

  As for the high temperature strength, good results were not obtained in Comparative Examples 3, 4 and 13. This is considered to be mainly due to the fact that the heat treatment temperature is 260 ° C. or higher and the film is over-aged.

  In contrast, in Examples 1 and 2 in which the heat treatment temperature was 240 ° C. or higher and 260 ° C. or lower and the heat treatment time was 1 hour or longer and 3 hours or shorter, the high temperature strength was 120% Mpa or more at 0.2% proof stress.

  Regarding the normal temperature fatigue strength, good results were not obtained in Comparative Examples 3 to 7, 10 to 17, 25, 28, 30 and 31. It is thought that this is mainly because the Si content exceeds 15.0 wt% (Comparative Examples 3, 5, 7, 11, 15, and 16). When the Si content exceeds 15.0 wt%, the toughness is lowered by the plate-like eutectic Si or coarse primary crystal Si, and the normal temperature fatigue strength is thereby lowered.

  In addition, it is thought that it was because Mg was insufficient that the favorable result was not obtained by Comparative Examples 10, 12, and 25 about normal temperature fatigue strength. It is also considered that the heat treatment temperature is higher than 260 ° C. and the heat treatment time is longer than 3 hours (Comparative Examples 4, 13, and 17).

  It is also considered that the Mn content is less than 1/2 of the Fe content (Comparative Examples 6 and 14). If the Mn content is less than ½ of the Fe content, needle-like Fe-based intermetallic compounds are deposited on the thick portion. In Comparative Example 18, the Mn content is less than ½ of the Fe content (the Fe content is 0.6 wt%, whereas the Mn content is 0.2 wt%). Sufficient room temperature fatigue strength was obtained, but this is thought to be because the amount of needle-like intermetallic compound was small because the Fe content was small.

On the other hand, the Si content is 15.0 wt% or less, the Mg content is 0.2 wt% or more, the Mn content is 1/2 or more of the Fe content, the heat treatment temperature is 260 ° C. or less, and the heat treatment time is 3 hours. In Examples 1 and 2 below, the 10 ⁷ times fatigue strength was 100 MPa or more. Thus, the Si content is 15.0 wt% or less, the Mg content is 0.2 wt% or more, the Mn content is 1/2 or more of the Fe content, the heat treatment temperature is 260 ° C. or less, and the heat treatment time is 3 It was confirmed that the fatigue strength can be secured by setting the time to less than the time.

  As for thermal cycle fatigue strength, good results were not obtained in Comparative Examples 1 to 10, 14, 16, 22, and 26. This is because the Cu content is 2.0 wt% or more (Comparative Examples 1 to 9), the Sr content is less than 0.002 wt% (Comparative Example 26), and the Fe content is 1.0 wt%. Exceeding (Comparative Examples 3, 6, 8, 10, 14, 16, and 22) is the main cause. As already explained, when the Cu content exceeds 0.5 wt%, the thermal conductivity is lowered, and the thermal cycle fatigue strength is lowered at the same time. By adding Sr to the aluminum alloy, the metal structure can be refined to compensate for the decrease in thermal cycle fatigue strength. However, if the Sr content is less than 0.002 wt%, the effect cannot be sufficiently obtained. . On the other hand, if the Fe content exceeds 1.0 wt%, an intermetallic compound such as Al—Fe or Al—Fe—Si is generated and the toughness is lowered, thereby reducing the thermal cycle fatigue strength.

  On the other hand, in Examples 1 and 2 in which the Cu content is less than 2.0 wt%, the Sr content is 0.002 wt% or more, and the Fe content is 1.0 wt% or less, the normal temperature and 250 ° C. The allowable strain amount in the cycle was 0.4% or more, and good evaluation results were obtained for the thermal cycle fatigue strength. Thus, sufficient thermal cycle fatigue strength can be ensured by setting the Cu content to less than 2.0 wt%, the Sr content to 0.002 wt% or more, and the Fe content to 1.0 wt% or less. It was confirmed.

  As for machinability, good evaluation results were not obtained in Comparative Examples 3, 5, 7, 11, 15, 16, and 23. This is because the Si content exceeds 14.0 wt% (Comparative Examples 3, 5, 7, 11, 15, and 16), or the Mn content exceeds 0.6 wt% (Comparative Example). 23) is considered to be the cause. When the Si content exceeds 14.0 wt%, the machinability is deteriorated by the plate-like eutectic Si or coarse primary crystal Si. In addition, when the Mn content exceeds 0.6 wt%, a coarse intermetallic compound (Al—Fe—Mn) is deposited in a place where solidification is slow (a thick portion such as the combustion chamber wall 30). Thus, machinability is deteriorated.

  On the other hand, in Examples 1 and 2 in which the Si content was 14.0 wt% or less and the Mn content was 0.6 wt% or less, good evaluation results on the machinability were obtained. As described above, by setting the Si content to 14.0 wt% or less and the Mn content to 0.6 wt% or less, sufficient machinability is ensured even for a thick portion such as the combustion chamber wall 30. Confirmed to get.

  As for dimensional stability, good evaluation results were not obtained in Comparative Examples 1, 5, 8 to 10, 12, 14 to 16, 18 and 32. This is because the heat treatment temperature is less than 240 ° C. and the heat treatment time is less than 1 hour. If the heat treatment temperature is less than 240 ° C. or the heat treatment time is less than 1 hour, the material will grow permanently when a heat load higher than the heat treatment temperature is applied by the heat during engine operation.

  As described above, the aluminum alloy which is the material of the cylinder head body 100 is 8.0 wt% or more and 12.0 wt% or less of Si, 0.5 wt% or less of Cu, 0.002 wt% or more and 0.02 wt% or less of Sr. , 0.2 wt% or more and 0.5 wt% or less of Mg, 0.5 wt% or more and 1.0 wt% or less of Fe and 0.3 wt% or more and 0.6 wt% or less of Mn, The cylinder head main body 100 excellent in all of normal temperature strength, high temperature strength, normal temperature fatigue strength, thermal cycle fatigue strength, machinability and dimensional stability can be obtained.

  Moreover, as shown in Table 1, Table 3, Table 4, and Table 6, in Examples 1 and 2 where the heat treatment temperature is 240 ° C. or higher and the heat treatment time is 1 hour or longer, the heat treatment temperature is 240 ° C. Higher thermal conductivity was obtained than Comparative Example 32 having a temperature of less than ° C. and Comparative Example 33 having a heat treatment time of less than 1 hour. From this, it is understood that the heat treatment temperature is 240 ° C. or more and the heat treatment time is 1 hour or more, so that the effect of ensuring sufficient thermal conductivity and improving the cooling property can be obtained more reliably. .

  Furthermore, in Examples 1 and 2 in which the heat treatment temperature is 260 ° C. or less and the heat treatment time is 3 hours or less, Comparative Example 30 in which the heat treatment temperature exceeds 260 ° C. or Comparative Example 31 in which the heat treatment time exceeds 3 hours. Better room temperature strength was obtained. From this, it is understood that the dimensional stability required for the cylinder head body 100 can be ensured when the heat treatment temperature is 260 ° C. or less and the heat treatment time is 3 hours or less.

  Further, as in the present embodiment, the exhaust passage 50 extends away from the cam chain chamber 70 from the inlet side toward the outlet side, so that the space between the outlet of the exhaust passage 50 and the cam chain chamber 70 is increased. Can be spread. Therefore, it is easy to ensure a sufficiently large cross-sectional area of the cooling air passage 60. Therefore, sufficiently high cooling performance can be realized.

  Further, in the present embodiment, the exhaust passage 50 is formed such that its axis 50x is linear. Therefore, exhaust resistance is reduced, and more efficient combustion is possible. Further, when the cylinder head main body 100 is formed by die casting, the final-shaped exhaust passage 50 can be formed by a mold, so that it is not necessary to change the shape of the exhaust passage 50 by post-processing.

  Note that, from the viewpoint of ensuring a sufficiently large cross-sectional area of the cooling air passage 60, the axis 50x of the exhaust passage 50 is preferably inclined at a certain angle with respect to the front-rear direction. Specifically, the axis 50x of the exhaust passage 50 is 20 ° or more with respect to a straight line L3 connecting the centers of the two bolt holes 80a and 80b located on the cam chain chamber 70 side of the four bolt holes 80a to 80d. It is preferable to incline so that the angle may be made. However, if the inclination angle is too large, the exhaust resistance may become too large. Therefore, the inclination angle is preferably 30 ° or less.

  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 passage 50 and the cam chain chamber 70, the exhaust passage 50, the cam chain chamber 70, A part of the cooling air passage 60 needs to be positioned (arranged) in a space narrower than the space between them (that is, a space between the bolt hole 80a and the exhaust passage 50). However, as described above, since the exhaust passage 50 extends away from the cam chain chamber 70 from the inlet side toward the outlet side, the cooling air passage 60 is also provided between the bolt hole 80a and the exhaust passage 50. A sufficiently large cross-sectional area can be secured.

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

  The plurality of cooling fins 10 preferably include cooling fins 10 extending from an exhaust passage wall that defines the exhaust passage 50. Since the exhaust passage 50 is a portion that is likely to become high temperature in the cylinder head body 100, the cooling fin 10 extends from the exhaust passage wall, so that the cooling efficiency can be improved. More specifically, the cooling fin 10 extending from the exhaust passage wall is at least a bolt hole (closest to the cooling fin 10 extending from the exhaust passage wall) in the exhaust passage wall from the viewpoint of ensuring sufficiently high cooling efficiency. A boss (stud bolt boss) 80 corresponding to the bolt hole 80c extends from a portion located on the cylinder axis L1 side (see FIG. 10).

  Here, among the plurality of cooling fins 10, the cooling fin 10 a positioned on the combustion chamber 110 side with respect to the top of the combustion chamber wall 30 is referred to as “first cooling fin”, and combustion is performed on the top of the combustion chamber wall 30. The cooling fins 10b located on the side opposite to the chamber 110 (that is, the cam chamber side) are referred to as “second cooling fins”. In the present embodiment, as can be seen from FIGS. 8, 9, and 10, the plurality of cooling fins 10 has a total area of the first cooling fins 10a larger than a total area of the second cooling fins 10b. Is provided.

  During operation of the engine 101, in the cylinder head main body 100, the region on the combustion chamber 110 side with respect to the top of the combustion chamber wall 30 is the region opposite to the combustion chamber 110 with respect to the top of the combustion chamber wall 30. The temperature becomes higher than. For this reason, the total area of the first cooling fins 10a located in the former region is larger than the total area of the second cooling fins 10b located in the latter region, thereby effectively improving the cooling performance. it can.

  In the present embodiment, as shown in FIG. 10, the plurality of cooling fins 10 are viewed from the side opposite to the cam chain chamber 70 with respect to the cylinder axis L1 (viewed from a direction perpendicular to the paper surface in FIG. The end 10a1 of the first cooling fin 10a on the cylinder axis L1 side is provided closer to the cylinder axis L1 than the end 10b1 of the second cooling fin 10b on the cylinder axis L1 side. Yes. That is, the end portion 10b1 of the second cooling fin 10b is further away from the cylinder axis L1 than the end portion 10a1 of the first cooling fin 10a. As a result, the cross-sectional area of the cooling air passage 60 can be increased.

  Further, in the present embodiment, as shown in FIG. 10, a part of the cooling air passage 60 is an exhaust passage wall 51 that defines the exhaust passage 50, and an exhaust that intersects the cam chamber wall 20 so as to form an acute angle. It is defined by the passage wall 51. This provides the following advantages.

  Normally, when the shape of the cooling air passage is formed by a die during die casting, the portion of the die corresponding to the cooling air passage has a shape protruding from the other portion. The tip of the portion having such a protruding shape is likely to become high temperature due to the heat of the molten metal. In particular, if there is a corner at the tip, it may melt. Therefore, generally, the tip is designed so that its cross section is circular. However, as in this embodiment, by defining a part of the cooling air passage 60 with the exhaust passage wall 51 that intersects the cam chamber wall 20 so as to form an acute angle, the cross-sectional area of the cooling air passage 60 is increased. be able to. In this case, since both the cam chamber wall 20 and the exhaust passage wall 51 may be small in thickness, the problem of melting damage can be avoided.

  The cam chamber wall 20 preferably has a thickness of 2.5 mm or less. When the thickness of the cam chamber wall 20 is 2.5 mm or less, it is possible to more reliably prevent the mold corner from being melted. However, if the thickness of the cam chamber wall 20 is less than 1.5 mm, sufficient pressure resistance required for the cam chamber 109 cannot be obtained, and resistance to deformation stress generated by strain may be insufficient. The thickness of the cam chamber wall 20 is preferably 1.5 mm or more.

  Moreover, in this embodiment, since the cylinder head main body 100 is shape | molded by die-casting, the thickness and pitch of the cooling fin 10 can be made small and cooling property can be improved. Specifically, as shown in FIG. 14, when the thickness of each tip of the plurality of cooling fins 10 is t and the pitch of the plurality of cooling fins 10 is p, the tip of each cooling fin 10 is The thickness t is 1.0 mm or more and 2.5 mm or less, and the plurality of cooling fins 10 can be arranged at a pitch p of 7.5 mm or less.

  Each of the plurality of cooling fins 10 preferably has a draft angle of 2.0 ° or less. By reducing the draft to 2.0 ° or less, the interval at the root portion of the cooling fin 10 can be increased, so that the cooling performance can be further improved. However, from the viewpoint of facilitating mold release, the draft angle of each of the plurality of cooling fins 10 is preferably 1.0 ° or more.

  Further, as shown in FIG. 10, the cylinder head body 100 in the present embodiment further includes a rib 90 provided in the cooling air passage 60 and connecting the combustion chamber wall 30 and the cam chamber wall 20. The rib 90 connects the combustion chamber wall 30 and the cam chamber wall 20, so that the rib 90 transfers the heat of the combustion chamber wall 30 to the cam chamber wall 20, and the cam chamber 109 can be cooled using lubricating oil. Therefore, the cooling property can be improved. In addition, since the rib 90 is disposed in the cooling air passage 60, a cooling effect by the cooling air CA is also obtained.

  In addition, it is preferable that the rib 90 is formed along the die cutting direction when the cylinder head main body 100 is shape | molded by die-casting. Therefore, the rib 90 is preferably formed along a wall portion (cooling air passage wall) that defines the cooling air passage 60.

  Further, the cross-sectional shape of the exhaust passage 50 along the plane orthogonal to the axis 50x of the exhaust passage 50 is substantially elliptical, and the shape of the outlet 50b of the exhaust passage 50 is substantially circular as shown in FIG. It is preferable that Since the cross-sectional shape of the exhaust pipe 142 is generally a perfect circle, the shape of the outlet 50b of the exhaust passage 50 is a substantially perfect circle, thereby preventing a rapid change in the passage area and preventing a decrease in the performance of the engine 101. can do. As already described, since the exhaust passage 50 extends away from the cam chain chamber 70 from the inlet side toward the outlet side, the cross-sectional shape of the exhaust passage 50 along the plane orthogonal to the axis 50x is substantially true. If it is a circle, the shape of the outlet 50b of the exhaust passage 50 cannot be a substantially perfect circle. When the cross-sectional shape of the exhaust passage 50 along the plane orthogonal to the axis 50x is substantially elliptical, that is, the roundness of the cross-sectional shape of the exhaust passage 50 along the plane orthogonal to the axis 50x is determined by the By making it lower than the roundness of the shape of the outlet 50b, the shape of the outlet 50b of the exhaust passage 50 can be made substantially circular.

  Further, it is also preferable to perform shot blasting on the wall portion defining the cooling air passage 60 and the cam chain chamber 109 and the outer surface including the plurality of cooling fins 10. The surface contact with the cooling air CA is increased by the roughening by the shot blasting process, so that the cooling performance can be further improved. Moreover, the deburring of the cooling air passage 60 can also be performed by shot blasting.

  In order to further improve the cooling performance, it is also preferable to provide cooling fins extending from the ribs 90 or to perform shot blasting on the ribs 90.

  The internal combustion engine 101 according to the embodiment of the present invention is suitably used for various straddle-type vehicles such as a motorcycle and an ATV (All Terrain Vehicle). Moreover, it is used suitably also for a generator etc.

  According to the present invention, an air-cooled single-cylinder internal combustion engine that can be operated at a high compression ratio and has excellent fuel efficiency is provided. The air-cooled single-cylinder internal combustion engine according to the present invention is suitably used for various straddle-type vehicles such as motorcycles.

1 Motorcycle (saddle-ride type vehicle)
DESCRIPTION OF SYMBOLS 10 Cooling fin 20 Cam chamber wall 30 Fuel chamber wall 32 Plug hole 40 Intake passage 40a Intake port 40b Opening 50 Exhaust passage 50a Exhaust port (inlet of exhaust passage)
50b Opening (exhaust passage outlet)
50x Exhaust passage axis 51 Exhaust passage wall 60 Cooling air passage 60a Cooling air passage inlet 60b Cooling air passage outlet 70 Cam chain chamber 80 Head bolt boss 80a, 80b, 80c, 80d Bolt hole 90 Rib 100 Cylinder head body 101 Engine (Internal combustion engine)
102 Crankcase 103 Cylinder block 104 Cylinder head 105 Cylinder head cover 106 Cylinder 108 Cam shaft 109 Cam chamber 110 Combustion chamber 113 Cam chain 121 Cooling fan 130 Shroud 141 Intake pipe 142 Exhaust pipe 151 Intake valve 152 Exhaust valve CA Cooling air D1 Cylinder axial direction L1 Cylinder axis

Claims (7)

A plurality of cooling fins;
A cam chamber wall defining the cam chamber;
A combustion chamber wall defining the combustion chamber;
An intake passage for performing intake to the combustion chamber;
An exhaust passage for exhausting from the combustion chamber;
A cylinder head body having a cooling air passage for passing cooling air between the cam chamber wall and the combustion chamber wall;
The cylinder head body is integrally formed by die casting from an aluminum alloy,
The aluminum alloy includes 8.0 wt% or more and 12.0 wt% or less of Si, 0.5 wt% or less of Cu, 0.002 wt% or more and 0.02 wt% or less of Sr, 0.2 wt% or more of 0.5 wt% or less. Mg, 0.5 wt% to 1.0 wt% Fe and 0.3 wt% to 0.6 wt% Mn,
The thermal conductivity of the cylinder head body at 100 ° C. is 145 W / (m · K) or more,
An air-cooled single-cylinder internal combustion engine in which the Rockwell hardness of the cylinder head body at room temperature is 70 HRF or more and 90 HRF or less. Each tip of the plurality of cooling fins has a thickness of 1.0 mm or more and 2.5 mm or less,
The air-cooled single-cylinder internal combustion engine according to claim 1, wherein the plurality of cooling fins are arranged at a pitch of 7.5 mm or less.   3. The air-cooled single-cylinder internal combustion engine according to claim 1, wherein each of the plurality of cooling fins has a draft of not less than 1.0 ° and not more than 2.0 °.   The air-cooled single-cylinder internal combustion engine according to any one of claims 1 to 3, wherein a surface roughness Rz of an inner peripheral surface of the exhaust passage is 30 µm or less.   5. The air-cooled single-cylinder internal combustion engine according to claim 1, wherein the plurality of cooling fins include cooling fins extending from an exhaust passage wall that defines the exhaust passage.   A straddle-type vehicle comprising the air-cooled single-cylinder internal combustion engine according to any one of claims 1 to 5. 8.0 wt% to 12.0 wt% Si, 0.5 wt% or less Cu, 0.002 wt% to 0.02 wt% Sr, 0.2 wt% to 0.5 wt% Mg, 0.5 wt% A first step of preparing an aluminum alloy containing Fe of not less than 1.0% and not more than 1.0 wt% and Mn of not less than 0.3 wt% and not more than 0.6 wt%;
A plurality of cooling fins, a cam chamber wall defining a cam chamber, a combustion chamber wall defining a combustion chamber, an intake passage for performing intake air to the combustion chamber, and exhausting from the combustion chamber A second step of integrally forming a cylinder head body having an exhaust passage and a cooling air passage for passing cooling air between the cam chamber wall and the combustion chamber wall from the aluminum alloy by die casting; ,
After the second step, the cylinder head body is water-cooled, and then the cylinder head body is heat-treated at a temperature of 240 ° C. to 260 ° C. for 1 hour to 3 hours,
Of manufacturing an air-cooled single cylinder internal combustion engine.

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