JP5415363B2 - Cylinder head structure of internal combustion engine - Google Patents

Description

  The present invention relates to a cylinder head structure of an internal combustion engine mounted on a motorcycle or the like.

  Some cylinder heads of an engine (internal combustion engine) including a horizontal cylinder have a side wall and an upper wall formed integrally with each other (see, for example, Patent Document 1).

JP-A-5-15617

  A cylinder head of this type of internal combustion engine is required to have high rigidity while improving cooling performance.

  An object of the present invention is to provide a cylinder head structure for an internal combustion engine that can reduce the weight while securing the rigidity of the cylinder head and can improve the cooling performance of the cylinder head.

  As a means for solving the above problems, the invention according to claim 1 is a pair of support walls (50, 51) for supporting the cam shaft (44) and the support wall (50) so as to cover the cam shaft (44). , 51) and four bolts formed so as to penetrate from the upper wall (67) side toward the cam shaft (44) and surround the cam shaft (44). A hole (81) and four bolt bosses (80) projecting from the upper wall (67) and opening the bolt insertion hole (81), and a fastening bolt is inserted into the bolt insertion hole (81) to crank In the cylinder head (21) of the internal combustion engine (17) fastened to the case (19), a concave portion (90) and a convex portion (91) are formed on the outer surface of the upper wall (67), and the concave portion (90) The boundary (S1) of the convex portion (91) connects the bolt boss (80). Characterized in that it is formed along the two diagonals (L1, L2).

  According to a second aspect of the present invention, the concave portion (90) is formed in a substantially triangular shape along two sides along two diagonal lines (L1, L2) connecting the bolt boss (80), and the triangular concave portion ( A pair of triangular recesses (90) are formed on the outer surface of the upper wall (67) so that the vertices (P1, P2) of 90) face each other across the intersection (P3) of the diagonal lines (L1, L2). It is characterized by.

  The invention according to claim 3 is used in an air cooling engine (17), and air cooling fins (92) parallel to a straight line (L3) connecting the adjacent bolt bosses (80) to the outer surface of the upper wall (67). The air cooling fin (92) is formed in the recess (90).

  According to a fourth aspect of the present invention, an intake rocker arm (41) and an exhaust rocker arm (42) are disposed between the cam shaft (44) and the upper wall (67), and intake and exhaust valves (39, 40). Used for the SOHC engine (17) that opens and closes the exhaust, and the exhaust-side rocker arm shaft (82) that supports the intake rocker arm (41) so as to swing and the exhaust that supports the exhaust rocker arm (42) so as to swing. Rocker arm shaft support portions (84, 85) for supporting the side rocker arm shaft (83) are formed in the support walls (50, 51), and the bolt insertion holes (81) are formed on the rocker arm shaft support portions (84, 85). 85).

  According to a fifth aspect of the present invention, a spark plug (66) is provided on a side wall (62A) located on one side of the support wall (51) and closer to the crankcase (19) than the support wall (51). A fastening hole (66) is provided, and the bolt insertion hole (81) adjacent to the fastening hole (65) functions as an oil supply oil passage (96) through which oil is supplied from the crankcase (19). Features.

  The invention according to claim 6 extends along the straight line (L3) connecting the adjacent bolt boss (80) to the support wall (51) on the one side, and one end of the oil supply oil passage (96). And an oil passage (93) in the head that is communicated with the bolt insertion hole (81) functioning as the upper end of the valve operating chamber (94) in which the cam shaft (44) is accommodated. It is characterized by.

  According to the seventh aspect of the present invention, the support wall (51) on the one side extends along the oil passage (93) in the head and the inside of the head from the outside of the support wall (51). A side wall recess (97) that is recessed toward the oil passage (93) is formed.

According to the first aspect of the present invention, the boundary of the concave portion and the convex portion is formed so as to connect the bolt boss to the upper wall of the cylinder head, so that the rigidity of the cylinder head can be achieved without making the upper wall of the cylinder head thick. Can be high. Thereby, the weight of the cylinder head can be reduced, and the cooling performance of the cylinder head can be improved by the thin portion of the upper wall formed by the recess.
According to the invention described in claim 2, by forming a pair of substantially triangular recesses, by aligning the boundary between the recesses and the projections along the diagonal line of the bolt boss so that the substantially triangular recesses face the apex, The ratio of the recesses in the upper wall can be suppressed, the bolt bosses can be reinforced so that the distance between the diagonal bolt bosses is not widened, and the rigidity of the cylinder head can be increased.
According to invention of Claim 3, it can reinforce so that the space | interval of adjacent bolt boss | hubs may not spread with an air cooling fin. In addition, the size of the air cooling fin can be increased while maintaining the appearance.
According to the fourth aspect of the present invention, the bolt includes a support wall that supports the camshaft, and a bolt boss that projects from the upper wall that opens the bolt insertion hole formed so as to surround the rocker arm shaft support portion. By increasing the rigidity between the insertion holes, the opening and closing timing of the valves opened and closed by the intake rocker arm and the exhaust rocker arm can be improved.
According to the fifth aspect of the present invention, the heat around the spark plug can be cooled by the oil passing through the bolt insertion hole adjacent to the spark plug, and the cooling performance of the cylinder head can be improved.
According to the sixth aspect of the present invention, it is possible to improve the lubrication of the valve operating chamber by dripping the oil from the upper portion of the valve operating chamber through the oil passage in the head.
According to the seventh aspect of the present invention, it is possible to improve the heat dissipation of the oil passing through the oil passage in the head and to promote the cooling of the oil supplied to the valve operating chamber.

1 is a left side view of a motorcycle according to an embodiment of the present invention. Fig. 3 is a left side view around the engine of the motorcycle. It is a longitudinal cross-sectional view of the cylinder head of the engine along the AA line of FIG. It is a front view of a cylinder head. It is a left view of a cylinder head. It is a right view of a cylinder head. It is sectional drawing which follows the BB line of FIG. It is sectional drawing which follows the CC line of FIG. It is sectional drawing which follows the DD line | wire of FIG. It is a top view of a cylinder head. It is sectional drawing which follows the EE line | wire of FIG. It is explanatory drawing for demonstrating the connection of an intake pipe at the time of changing the specification of the intake air amount adjustment apparatus of a motorcycle, and is a left view of a motorcycle.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, directions such as front, rear, left and right are the same as those in the vehicle unless otherwise specified. In the figure, the arrow FR indicates the front of the vehicle, the arrow LH indicates the left side of the vehicle, and the arrow UP indicates the upper side of the vehicle.

  FIG. 1 is a left side view of a motorcycle 1 having a structure according to this embodiment. The motorcycle 1 includes a so-called underbone type body frame 2, and a pair of left and right front forks 5 that pivotally support the front wheels 4 are steered via a steering stem 6 on a head pipe 3 positioned at the front end of the body frame 2. It is pivotally supported. A steering bar handle 7 is attached to the upper portion of the steering stem 6.

  One main frame 8 extends obliquely downward and rearward from the head pipe 3, and a pair of left and right pivot plates 9 extend downward from the rear end portion of the main frame 8. A front end portion of a swing arm 11 that pivotally supports the rear wheel 10 is pivotally supported at the upper and lower intermediate portions of the pivot plate 9. The front end portions of the seat rail 12a and the pair of left and right support pipes 12b are joined to each other.

  A pair of left and right cushion units 13 are disposed between the front and rear intermediate portion of the seat frame 12 and the rear end portion of the swing arm 11, and a passenger seat 14 is disposed above the seat frame 12. The vehicle body of the motorcycle 1 is covered with a vehicle body cover 15 made of synthetic resin. In the figure, reference numeral 14a indicates a luggage box disposed below the front portion of the seat 14, and reference numeral 16 indicates a fuel tank disposed below the rear portion of the seat 14.

  An air-cooled single-cylinder engine 17 having the structure according to the present embodiment is mounted below the main frame 8 of the vehicle body frame 2, and the engine 17 has a rotation axis (crank axis) C1 of the crankshaft 18 along the left-right direction. The cylinder block 20 is arranged in a state, and has a basic configuration in which the cylinder block 20 protrudes forward from the front end portion of the crankcase 19 substantially horizontally (in detail, slightly upward) (horizontal cylinder). In addition, the code | symbol C2 in the figure has shown the axis line (cylinder axis line) along the protrusion direction of the cylinder in the cylinder block 20. FIG.

  In the engine 17, the cylinder block 20 has a cylinder head 21 attached to a front end portion thereof. The cylinder head 21 has a trapezoidal shape in a side view and has a structure in which a head cover and a cylinder header are integrated.

One end of the intake pipe 22 is connected to the upper side (intake side) of the cylinder head 21, and the other end of the intake pipe 22 is connected to the downstream side of the carburetor 23. One end of a connecting tube 24 is connected to the upstream side of the carburetor 23, and the other end of the connecting tube 24 is connected to an air cleaner case 25.
One end of an exhaust pipe 26 is connected to the lower side (exhaust side) of the cylinder head 21, and the exhaust pipe 26 extends rearward under the engine 17, and the other end is disposed on the right side of the rear wheel 10. It is connected to the silencer 27. The air cleaner case 25 is supported on the upper part of the main frame 8 via a bracket (not shown).

Referring to FIG. 2, a cylinder bore 28 is formed in the cylinder block 20 along the cylinder axis C <b> 2, and a piston 29 is slidably fitted in the cylinder bore 28. The piston 29 is connected to the crankshaft 18 via a connecting rod 30.
The rotational power of the crankshaft 18 is supplied to a drive sprocket 32 disposed on the left side of the rear portion of the crankcase 19 via a clutch (not shown) disposed on the right side in the crankcase 19 and a transmission 31 disposed on the rear portion in the crankcase 19. To the driven sprocket 34 on the left side of the rear wheel 10 through the drive chain 33 (see FIG. 1).

  In FIG. 2, reference numeral 35 denotes a main shaft constituting the transmission 31, and reference numeral 36 denotes a counter shaft constituting the transmission 31. The upper center of the crankcase 19 is supported by an engine hanger 48 formed on the main frame 8, and the rear portion of the crankcase 19 is supported by a pair of upper and lower fastening portions 49 formed on the pivot plate 9.

  An intake port 37 to which the carburetor 23 is connected is formed at the upper part of the cylinder head 21, and an exhaust port 38 to which the exhaust pipe 26 is connected is formed at the lower part of the cylinder head 21. Each port 37, 38 opens from the side wall of the cylinder head 21 and opens to the combustion chamber 21 </ b> A in the cylinder head 21. The cylinder inner openings (combustion chamber 21A side openings) of the ports 37 and 38 can be opened and closed by an intake valve 39 and an exhaust valve 40, respectively. Opening and closing operations of the ports 37 and 38 by the valves 39 and 40 are performed by a single camshaft 44 via the intake rocker arm 41 and the exhaust rocker arm 42.

  The cam shaft 44 is arranged with its rotation axis C3 along the left-right direction (parallel to the crankshaft 18), and is shown in a longitudinal sectional view of the cylinder head 21 along the line AA in FIG. 2 shown in FIG. Thus, it is arranged on the upper side of the combustion chamber 21A (when the top side of the cylinder head 21 is viewed as the upper side). The engine 17 is a SOHC engine.

  As shown in FIG. 3, the cam shaft 44 is supported by a pair of left and right left support walls 50 and 51 that are formed integrally with the cylinder head 21, and the left support wall 50 has a left end portion side of the cam shaft 44. A fitting hole 53 of a ball bearing 52 that is rotatably supported is provided therethrough, and a fitting hole 55 of a ball bearing 54 that rotatably supports the right end portion of the cam shaft 44 is formed in the right support wall 51. ing.

  A cam chain chamber 56 is formed on the left side of the left support wall 50, and an opening 57 for assembling or receiving the cam shaft 44 is formed in the left side wall 70 exposed to the outside on the left side of the cam chain chamber 56. Yes. The cam shaft 44 is inserted from the opening 57, passes through the fitting hole 53 of the left support wall 50, and is supported by the left and right support walls 50 and 51 via the ball bearings 52 and 54. A bolt fastening hole 50A is formed in the left support wall 50, and a plate 50B straddling the left support wall 50 and the ball bearing 52 is fastened by a bolt 50C. Thereby, the position of the cam shaft 44 is fixed.

A cam driven sprocket 45 (not shown) having a relatively large diameter is coaxially fixed to the left end portion of the cam shaft 44, and a cam drive sprocket 46 having a relatively small diameter coaxially fixed to the left side portion of the cam driven sprocket 45 and the crankshaft 18 ( 2), an endless cam chain 47 is wound around.
The camshaft 44 is linked to the crankshaft 18 by the sprockets 45 and 46 and the cam chain 47, and the valves 39 and 40 are opened and closed. The cam shaft 44 is a solid shaft body formed by casting, and sufficient rigidity is ensured. The cam driven sprocket 45 is fixedly supported by a bolt 45A fastened to one bolt fastening hole 44A drilled in the axial direction from the left end surface of the cam shaft 44.

  After the cam shaft 44 is supported in the cylinder head 21, the head cap 58 is attached to the left side wall of the cylinder head 21 so as to close the opening 57 (see also FIG. 2). The head cap 58 integrally has an annular engagement wall 59 that engages with the inner peripheral edge of the opening 57 on the back surface thereof, and is engaged with the engagement wall 59 and screwed thereto. A groove 60 is formed on the outer peripheral side of the engagement wall 59, and a seal member 61 is provided in the groove 60.

  In the cylinder head 21, the left support wall 50 and the right support wall 51 are arranged in parallel with a certain distance apart in the axial direction of the cam shaft 44, and are erected integrally with a bottom wall portion 62 in which the combustion chamber 21 </ b> A is formed. . An air jacket 63 that is recessed from the right side is formed in the bottom wall portion 62, and the combustion chamber 21A side of the air jacket 63 is formed to be curved along the outer edge of the combustion chamber 21A.

  A spark plug fastening hole 65 communicating with the combustion chamber 21A is formed in a curved side wall 62A located on the right side of the bottom wall 62 formed so as to be recessed by forming the air jacket 63. A spark plug 66 is fastened to the spark plug fastening hole 65, and this spark plug 66 is directed toward the right front side in the vehicle-mounted state of the engine 17. Further, a hollow portion constituting a part of the cam chain chamber 56 is formed on the left side of the combustion chamber 21 </ b> A in the bottom wall portion 62.

  The left side support wall 50 and the right side support wall 51 are integrally connected at their distal ends by an upper wall 67 provided so as to cover the camshaft 44. Here, when the engine 17 is mounted on a vehicle, The upper wall 67 is directed forward, but is referred to as an “upper wall” on the basis of the case where the cylinder head 21 is viewed as a single unit. In the following description of the cylinder head 21, the direction of the cylinder head 21 will be described using the direction of the vehicle.

  4 is a front view of the cylinder head 21 as viewed from the front of the vehicle in the direction of the cylinder axis C2, and FIGS. 5 and 6 are a left side view and a right side view of the cylinder head 21, respectively. As shown in FIGS. 4 to 6, in the cylinder head 21, the left side wall 70, the left side support wall 50, and the right side support wall 51 are coupled to the upper wall 67. Further, an upper side wall 71 positioned on the upper side and a lower side wall 72 positioned on the lower side are coupled to the upper wall 67, the left side wall 70, the left side support wall 50, and the right side support wall 51. The right support wall 51 also serves as a wall exposed to the outside.

As described above, the cylinder head 21 has a trapezoidal shape when viewed from the side, and the upper side wall 71 extends from the front end of the planar portion 73 toward the upper wall 67 with the planar portion 73 extending substantially parallel to the cylinder axis C2 when viewed from the side. The lower side wall 72 extends substantially parallel to the cylinder axis C2 in a side view, and the upper wall 67 extends from the front end of the flat portion 75. Such a shape is exhibited by having the inclined surface portion 76 that extends upward toward the front.
In the inclined surface portions 74 and 76, work openings 77 and 78 used for the assembly work of the intake valve 39 and the exhaust valve 40 are formed, respectively. These work openings 77 and 78 are closed with a lid at the end of the assembly work. The

  In the four corners of the upper wall 67, specifically, in the vicinity of the region where the upper wall 67 and the upper side wall 71 are coupled, and in the vicinity of the region where the upper wall 67 and the upper side wall 71 are coupled, the cylinder axis line extends from the upper wall 67. Four bolt bosses 80 projecting in the C2 direction are formed.

  7 is a cross-sectional view taken along the line BB in FIG. 4, and FIG. 8 is a cross-sectional view taken along the line CC in FIG. The bolt boss 80 is formed with bolt insertion holes 81... That open at one end to the front end surface of the bolt boss 80 and penetrate from the upper wall 67 toward the cam shaft 44 side to the lower portion of the cylinder head 21. Further, the bolt insertion holes 81 are formed so as to surround the cam shaft 44, and are arranged so as to form a rectangle when the centers are connected. Further, when the bolt boss 80 is viewed in the direction of the cylinder axis C <b> 2, the bolt boss 80 is disposed so as to surround the cam shaft 44 in the axial extension.

The cylinder head 21 is fastened to the crankcase 19 by inserting a bolt insertion hole 81 into a stud bolt (not shown) extending from the crankcase 19 in the direction of the cylinder axis C2 and screwing a nut to the front end surface of the bolt boss 80. It has become.
In FIG. 8, the intake-side rocker arm shaft support portion 84, the intake-side rocker arm shaft 82 that supports the intake-side rocker arm shaft 82, the exhaust-side rocker arm shaft 83, and the exhaust-side rocker arm shaft 83 are supported. A side rocker arm shaft support 85 is shown. The intake side rocker arm shaft support portion 84 and the exhaust side rocker arm shaft support portion 85 are holes formed in the axial direction of the cam shaft 44 from the left support wall 50. The rocker arm shaft support portion 85 is also surrounded by bolt insertion holes 81 arranged at the four corners as shown in FIG.

  Referring to FIG. 4 again, on the surface (outer surface) of the upper wall 67 in the cylinder head 21, a pair of concave portions 90 and a pair of convex portions 91 set with a high surface with respect to the concave portions 90 are integrally formed. Has been. FIG. 9 is a view showing a partial cross section of the upper wall 67 along the line DD in FIG. As shown in the figure, the bottom surface of the convex portion 91 is set higher than the concave portion 90.

  The boundary S1 between the concave portion 90 and the convex portion 91 is formed along two diagonal lines L1 and L2 that connect the bolt boss 80. Specifically, the concave portion 90 has two sides on the two diagonal lines L1 and L2 that connect the bolt boss 80. It is formed in a substantially triangular shape along the two sides, and a pair is formed on the upper wall 67 so that the vertices P1 and P2 of the two sides along the diagonal lines L1 and L2 face each other across the intersection point P3 of the diagonal lines L1 and L2. Yes. Thereby, the convex part 91 is formed so as to connect the bolt bosses 80 arranged in the horizontal direction and the vertical direction, and the bolt bosses 80 are reinforced.

  A plurality of air cooling fins 92 parallel to a straight line L3 connecting adjacent bolt bosses 80 arranged in the vertical direction are formed on the upper wall 67 of the cylinder head 21, and the air cooling fins 92 are connected to the recesses 90 and the protrusions 91. It is formed as follows. In addition, a plurality of air cooling fins are formed at appropriate positions on each side wall of the cylinder head 21.

  In FIG. 4, an oil passage 93 in the head extends along the straight line L <b> 3 connecting the adjacent bolt bosses 80 arranged in the vertical direction to the right support wall 51 adjacent to the spark plug 66 (the spark plug fastening hole 65). Is formed. Referring also to FIG. 8, the head oil passage 93 has one end communicating with a bolt insertion hole 81 formed on the lower side (exhaust port 38 side) of the right support wall 51 and the other end bent to the inside of the cylinder head 21. The connecting oil passage 95 is opened at the upper part of the valve operating chamber 94 in which the cam shaft 44 is accommodated. The valve operating chamber 94 refers to a space formed by the bottom wall portion 62, the left support wall 50, the right support wall 51, and the upper wall 67 with reference to FIG. 3.

  Here, the bolt insertion hole 81 through which the head internal oil passage 93 communicates functions as an oil supply oil passage 96 to which oil is supplied from the crankcase 19, and the oil supply oil passage 96 to the head internal oil passage 93. The oil (for lubrication) supplied to is supplied from the connecting oil passage 95 to the valve operating chamber 94 so that the camshaft 44 and the like are lubricated. 6 and 8, the right side support wall 51 has a side wall recess 97 extending along the head inner oil passage 93 and recessed from the outside of the right support wall 51 toward the head inner oil passage 93. Is formed.

  By the way, referring to FIG. 10, the upper side wall 71 of the cylinder head 21 is shown, and the intake pipe 22 extending from the downstream side of the carburetor 23 shown in FIG. To the intake port 37 that opens from the front. A disc-shaped flange that extends in the outer diameter direction is formed at the end of the intake pipe 22, and a pair of bolts formed so as to face each other on a straight line that passes through the center (opening center) of the intake pipe 22. A hole is formed (not shown). Hereinafter, a connection structure between the intake pipe 22 and the intake port 37 will be described.

  Around the inlet side opening 100 of the intake port 37 is formed a substantially circular seat surface portion 101 provided so as to protrude from the plane portion 73 and abutting the end surface of the intake pipe 22. Is formed with a pair of first boss portions 102 which are formed to be flush with the seat surface portion 101 and are substantially opposed to each other across the center C4 along a first straight line L4 passing through the center C4 of the intake port 37. Has been.

The first boss portion 102 is formed so as to protrude from the flat surface portion 73 and is positioned so as to protrude in the outer diameter direction of the seat surface portion 101. Bolt fastening holes 103 are respectively formed in the first boss portions 102, and the front end surface of the first boss portion 102 is a seat surface of a bolt insertion hole formed in the flange of the intake pipe 22, and is inserted into the bolt insertion hole. The intake pipe 22 is connected by fastening the bolt 120 (FIG. 2) to the bolt fastening hole 103.
Here, the straight line L5 indicates a straight line that is orthogonal to the cylinder axis C2 and extends substantially parallel to the flat surface portion 73 of the upper side wall 71 (extends in a substantially horizontal direction when the vehicle is mounted). The first straight line L4 extends at a predetermined angle in a clockwise direction with respect to the straight line L5, and the first boss portion 102 is specifically formed on the first straight line L4.

  Here, in the cylinder head 21, a second boss portion 104 having a formation interval and a formation position different from that of the first boss portion 102 is formed around the inlet side opening 100 of the intake port 37 (see FIGS. 5 and 11). The second boss portion 104 intersects the first straight line L4 and is formed so as to be substantially opposed to the second straight line L6 passing through the center C4 of the intake port 37 with the center C4 interposed therebetween.

  The second boss portion 104 is formed so as to protrude from the flat surface portion 73 in the same manner as the first boss portion 102, and is located in the outer diameter direction of the seat surface portion 101. A groove 105 (FIG. 10) is formed between them and is spaced apart. A second straight line L6 passing through the center C4 of the intake port 37 connecting the second boss portions 104 extends at a predetermined angle in a counterclockwise direction with respect to the straight line L5, and the first straight line L4 and the second straight line L6. In the present embodiment, the angle θ1 formed by the above is 40 °, but is preferably 45 ° or less. Further, as is apparent from the drawing, the distance between the second boss portions 104 is set longer than the distance between the first boss portions 102.

  The second boss part 104 is a thick part for forming a bolt fastening hole for fastening the intake pipe. In this embodiment, the bolt fastening hole is not formed, but the bolt fastening as shown in FIG. Hole 106 can be formed. In the present embodiment, the engine 17 has a carburetor specification, but the second boss portion 104 is provided to form the bolt fastening hole 106 when the specification uses the fuel injection device (injector). Yes.

  More specifically, FIG. 12 shows a motorcycle 111 equipped with an injector 110. The motorcycle 111 has the same configuration except that the carburetor 23, which is an intake air amount adjusting device of the motorcycle 1, is replaced by the injector 110. Comparing FIG. 2 and FIG. 12, the shape of the intake pipe 22 of the motorcycle 1 and the intake pipe 112 of the motorcycle 111 are different. In such a case, if the bolt fastening hole 106 is formed in the second boss portion 104 and fastened by the bolt 121, the intake pipe 112 can be attached without changing the basic configuration of the cylinder head 21.

  5, 10, and 11, between the first boss portion 102 located on the left side with respect to the cylinder axis C <b> 2 of the intake port 37 and the second boss portion 104 adjacent thereto, A thin tube support portion 113 that connects the first boss portion 102 and the second boss portion 104 is formed.

  The thin tube support portion 113 extends from the peripheral portion of the seat surface portion 101 and the side portion of the first boss portion 102 so as to be orthogonal to the cylinder axis C2 and substantially parallel to the flat portion 73 of the upper side wall 71 (when mounted on the vehicle). It protrudes along a straight line L5 (extending substantially in the horizontal direction), and a part thereof is coupled to the second boss 104. In the thin tube support portion 113, a pore 115 for supporting the thin tube 114 communicating with the intake port 37 is formed along the straight line L5, and the thin tube 114 is supported along the straight line L5. That is, the narrow tube 114 is disposed so as to be substantially parallel to the straight line L5 orthogonal to the cylinder axis C2 and along the flat surface portion 73 of the upper side wall 71 where the first boss portion 102 and the second boss portion 104 are formed. Yes.

  The narrow tube 114 is connected to a connecting hose 116 connected to the fuel tank 16 constituting the evaporation system so that the cylinder head 21 is separated at the end. The evaporation system includes a valve body, and the pressure in the fuel tank 16 is released to the intake port 37 by opening and closing the valve body as appropriate.

  In the embodiment described above, the upper wall 67 of the cylinder head 21 is made thick by forming the boundary S1 of the concave portion 90 and the convex portion 91 so as to connect the bolt boss 80 to the upper wall 67 of the cylinder head 21. Therefore, the rigidity of the cylinder head 21 can be increased. Accordingly, the weight of the cylinder head 21 can be reduced, and the cooling performance of the cylinder head 21 can be improved by the thin portion of the upper wall 67 formed by the recess 90. Further, by making the boundary between the concave portion 90 and the convex portion 91 along the diagonal lines L1 and L2 of the bolt boss 80, the appearance can be improved.

  Further, a pair of substantially triangular recesses 90 are formed, and the boundary S1 between the recesses 90 and the protrusions 91 is aligned with the diagonal lines L1 and L2 of the bolt boss 80 so that the approximately triangular recesses 90 face the apexes P1 and P2. Thus, the ratio of the concave portions 90 in the upper wall 67 can be suppressed, the bolt bosses 80 can be reinforced so that the distance between the diagonal bolt bosses 80 is not widened, and the rigidity of the cylinder head 21 can be increased.

  Also, air cooling fins 92 parallel to a straight line (L3) connecting adjacent bolt bosses 80 are formed on the upper wall 67, and the air cooling fins 92 are formed at least in the recesses 90. It can reinforce so that the space | interval of 80 may not spread. Moreover, the air-cooling fin 92 can be enlarged while maintaining the appearance.

Also, the rocker arm shaft support portions 84 and 85 for supporting the intake side rocker arm shaft 82 for swingably supporting the intake rocker arm 41 and the exhaust side rocker arm shaft 83 for swingably supporting the exhaust rocker arm 42 are on the left side. A bolt insertion hole 81 is formed in the support wall 50 so as to surround the rocker arm shaft support portions 84 and 85.
According to this, the bolt insertion is performed by the support wall that supports the cam shaft 44 and the bolt boss 80 that protrudes from the upper wall 67 that opens the bolt insertion hole 81 formed so as to surround the rocker arm shaft support portions 84 and 85. By increasing the rigidity between the holes 81, the opening and closing timing of the valves 39 and 40 opened and closed by the intake rocker arm 41 and the exhaust rocker arm 42 can be improved.

  Further, by causing the bolt insertion hole 81 adjacent to the spark plug 66 to function as an oil supply oil passage 96 to which oil is supplied from the crankcase 19, the heat around the ignition plug 55 is transferred to the bolt insertion hole adjacent to the ignition plug 66. It is possible to cool with oil that passes through the inside of the cylinder 81 and to improve the cooling performance of the cylinder head 21. In addition, an in-head oil passage 93 is formed which communicates one end with the bolt insertion hole 81 and opens the other end to the upper portion of the valve operating chamber 94. According to this, oil can be dripped from the upper part of the valve operating chamber 94 through the oil passage 93 in the head, and the valve operating chamber 94 can be lubricated well.

  The right support wall 51 in which the head internal oil passage 93 is formed has a side wall recess 97 extending along the head internal oil passage 93 and recessed from the outside of the support wall to the head internal oil passage 93 side. Is formed. According to this, the heat dissipation of oil passing through the in-head oil passage 93 can be improved, and cooling of the oil supplied to the valve operating chamber 94 can be promoted.

17 Internal combustion engine 19 Crankcase 21 Cylinder head 41 Intake rocker arm 42 Exhaust rocker arm 44 Cam shaft 50 Left support wall (support wall)
51 Right support wall (support wall)
62A Side wall 66 Spark plug 67 Upper wall 80 Bolt boss 81 Bolt insertion hole 82 Intake side rocker arm shaft 83 Exhaust side rocker arm shaft 84, 85 Rocker arm shaft support 90 Recess 91 Protrusion 92 Air cooling fin 93 Head oil passage 97 Side wall recess S1 border L1, L2 diagonal

Claims (7)

  A pair of support walls (50, 51) supporting the cam shaft (44), an upper wall (67) connecting the support walls (50, 51) so as to cover the cam shaft (44), and the upper wall Four bolt insertion holes (81) are formed so as to penetrate from the (67) side toward the cam shaft (44) side and surround the cam shaft (44), and the bolts projecting from the upper wall (67) The cylinder head of the internal combustion engine (17), which has four bolt bosses (80) in which the insertion holes (81) are opened, and is fastened to the crankcase (19) by inserting fastening bolts into the bolt insertion holes (81). (21), a concave portion (90) and a convex portion (91) are formed on the outer surface of the upper wall (67), and the boundary (S1) between the concave portion (90) and the convex portion (91) is the bolt boss (80). Formed along two diagonal lines (L1, L2) A cylinder head structure for an internal combustion engine characterized by and.   The concave portion (90) is formed in a substantially triangular shape along two sides along two diagonal lines (L1, L2) connecting the bolt boss (80), and apexes (P1, P2) of the triangular concave portion (90) A pair of the triangular recesses (90) is formed on the outer surface of the upper wall (67) so as to face each other across the intersection (P3) of the diagonal lines (L1, L2). 2. A cylinder head structure for an internal combustion engine according to 1.   An air cooling fin (92) used in the air cooling engine (17) and parallel to a straight line (L3) connecting the adjacent bolt bosses (80) is formed on the outer surface of the upper wall (67), and the air cooling fin (92) The cylinder head structure for an internal combustion engine according to claim 1 or 2, characterized in that is formed in the recess (90).   An SOHC engine (17) that opens and closes intake and exhaust valves (39, 40) by disposing an intake rocker arm (41) and an exhaust rocker arm (42) between the cam shaft (44) and the upper wall (67). An intake-side rocker arm shaft (82) that swingably supports the intake rocker arm (41) and an exhaust-side rocker arm shaft (83) that swingably supports the exhaust rocker arm (42). Rocker arm shaft support portions (84, 85) are formed on the support walls (50, 51), and the bolt insertion holes (81) are formed so as to surround the rocker arm shaft support portions (84, 85). The cylinder head structure for an internal combustion engine according to any one of claims 1 to 3, wherein   A fastening hole (65) of a spark plug (66) is provided on a side wall (62A) located on one side of the support wall (51) and closer to the crankcase (19) than the support wall (51), The bolt insertion hole (81) adjacent to the fastening hole (65) functions as an oil supply oil passage (96) through which oil is supplied from the crankcase (19). A cylinder head structure for an internal combustion engine according to any one of the preceding claims.   The bolt insertion hole (extending along a straight line (L3) connecting the adjacent bolt bosses (80) to the support wall (51) on the one side, and having one end functioning as the oil supply oil passage (96) ( 81) and an oil passage in the head (93) is formed in which the other end is opened to an upper portion of the valve operating chamber (94) in which the cam shaft (44) is accommodated. 6. A cylinder head structure for an internal combustion engine according to 5.   A side wall which extends along the oil passage (93) in the head to the support wall (51) on the one side and is recessed toward the oil passage (93) in the head from the outside of the support wall (51). A cylinder head structure for an internal combustion engine according to claim 6, wherein a recess (97) is formed.

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