Title of Invention

"A COOLING AIRFLOW PASSAGE STRUCTURE FOR A CYLINDER HEAD OF AN AIR-COOLED TYPE INTERNAL COMBUSTION ENGINE"

Abstract

To propose a structure enabling a further enhancement of air-cooling effect, in a cooling airflow passage structure for a cylinder head in an air-cooled type internal combustion engine including a combustion chamber at a lower portion, a valve chamber at an upper portion, a cam chain chamber at a side portion, an exhaust port in a front portion of an area between the combustion chamber and the valve chamber, and an intake port in a rear portion of the area. [Solving Means] An exhaust port is disposed away from a cam chain chamber, the area between the exhaust port and the cam chain chamber is made to be a front opening, an intake port is disposed close to the cam chain chamber, the side opposite to the cam chain chamber of the intake port is made to be a rear opening, a front-rear direction cooling airflow passage is provided which connects the front opening and the rear opening to each other, and a sidewise cooling airflow passage is provided which branches off sideways from a roughly central portion of the front-rear direction cooling airflow passage and is

Full Text

The present invention relates to a cooling airflow passage structure for a cylinder head of an air-cooled type internal combustion engine. The present invention relates to a cooling airflow passage structure for a cylinder head of an air-cooled type four-stroke-cycle internal combustion engine to be mounted on a motorcycle or the like. [Background Art] In an air-cooled type four-stroke-cycle internal combustion engine, a valve and a cam and a cylinder head cover for covering them are provided at a cylinder head portion, so that, generally, the running airflows would not easily come into contact with a high-temperature portion adjacent to the upper side of a ceiling portion of the combustion chamber in the condition where the internal combustion engine is mounted on a motorcycle or the like. ' 1 , V 1 As an example of the conventional airflow passage, an airflow passage with the following configuration has been known. In the internal combustion engine, two exhaust ports and two exhaust valves corresponding thereto are provided side by side at front portions of a cylinder head, while two intake ports and two intake valves corresponding thereto are provided side by side at rear portions of the cylinder head, a spark plug is provided at a position surrounded by the four valves, a camshaft directed in the left-right direction is provided between the cylinder head and a cylinder head cover, a cooling airflow passage is provided which passes between the two exhaust valves and between the two intake valves and penetrates through the cylinder head in the front-rear direction, and a sidewise cooling airflow passage is provided which is communicated with the front-rear direction cooling airflow passage (see Patent Document 1) In this example, the cylinder head is provided with a spark plug mounting/dismounting hole surrounding a main body portion of the spark plug with a gap around the main body portion, and the spark plug mpunting/dismounting hole is also communicated with the front-rear direction cooling airflow passage. [0004] In this internal combustion engine, when it is mounted on a motorcycle and the motorcycle runs, air . flows in through the front opening of the front-rear direction cooling airflow passage, a portion of the air passes through the spark plug mounting/dismounting hole to the upper outer side of the internal combustion engine, another portion of the air passes through the sidewise cooling airflow passage to a lateral outer side of the internal combustion engine, and the remainder of the air passes through the rear opening of the front-rear cooling airflow passage to the rear side. In the process of these flows of air, the cylinder head and the spark plug are cooled. [0005] [Patent Document 1] Japanese Patent Publication No. Sho 62-43050 (Figs. 2 and 3) [Disclosure of the Invention] [Problems to Be Solved by the Invention] [0006] According to the prior art, it is difficult for a sufficient amount of cooling airflow to pass through the cooling airflow passages. It is an object of the present invention to propose a structure which enables a further enhancement of the cooling effect in cooling airflow passages. [Means for Solving the Problems] [0007] The above-mentioned problems can be solved by the present invention. The invention as set forth in claim 1 resides in a cooling airflow passage structure for a cylinder head of an air-cooled type internal combustion engine, comprising a combustion chamber at a lower portion, a valve chamber at an upper portion, a cam chain chamber at a side portion, an exhaust port provided at a front portion of an area between the combustion chamber and the valve chamber, and an intake port provided at a rear portion of the area, characterized in that the exhaust port is disposed away from the cam chain chamber, an area between the exhaust port and the cam chain chamber being made to be a front opening; the intake port is disposed close to the cam chain chamber, the side opposite to the cam chain chamber of the intake port being made to be a rear opening; a front-rear direction cooling airflow passage is provided which connects the front opening and the rear opening to each other; and a sidewise cooling airflow passage is provided which branches off sideways from a roughly central portion of the front-rear direction cooling airflow passage and which is communicated with a side opening opened in a side surface of the cylinder head. [0008] The invention as set forth in claim 2 resides in a cooling airflow passage structure for a cylinder head as set forth in claim 1, characterized in that a shaft portion of a spark plug is exposed in the cooling airflow passage. [0009] The invention as set forth in claim 3 resides in a cooling airflow passage structure for a cylinder head as set forth in claim 1, characterized in that a secondary air supply port is provided to front on the cooling airflow passage. [0010] The invention as set forth in claim 4 resides in a cooling airflow passage structure for a cylinder head as set forth in claim 1, characterized in that a duct member enlarged in sectional area at a front portion thereof is provided at the front opening of the cooling airflow passage. [0011] The invention as set forth in claim 5 resides in a cooling airflow passage structure of a cylinder head for a two-cylinder internal combustion engine, comprising a cam chain chamber in a central area, and a cylinder head for cylinders being integrally formed on the left and right sides of said cam chain chamber, characterized in that combustion chambers are provided at left and right lower portions, valve chambers are provided at left and right upper portions, an exhaust port is provided at a front portion of an area between said combustion chamber and the valve chamber, an intake port is provided at a rear portion of the area, the exhaust port is disposed away from the cam chain chamber, and an area between the exhaust port and the cam chain chamber is made to be a front opening; the intake port is disposed close to the cam chain chamber, the side opposite to the cam chain chamber of the intake port is made to be a rear opening, a front-rear direction cooling airflow passage is provided which connects the front opening and the rear opening to each other on each of the left and right sides; and sidewise cooling airflow passages are provided which branch off sideways from a roughly central portion of the front-rear direction cooling airflow passage and are communicated respectively with side openings opened in both side walls of the cylinder head. [Effects of the Invention] [0012] According to the invention as set forth in claim 1, the exhaust port more raised in temperature than the intake port can be effectively cooled from both the left and right sides. In addition, since the combustion chamber can be cooled uniformly, it is possible to contrive an enhancement of combustion efficiency through an increase in compression ratio, restraint of emission of unburned materials, and restraint of knocking. [0013] According to the invention as set forth in claim 2, the cooling airflow passes smoothly on both sides of the shaft portion of the spark plug, so that the spark plug is cooled effectively. [0014] According to the invention as set forth in claim 3, a secondary air supply device and the secondary air supply port are cooled by the running airflow passing through the front-rear direction cooling airflow passage. [0015] According to the invention as set forth in claim 4, the enlarged front portion of the duct member makes it possible to collect the running air flow from a wide range and pass the running airflow into a running airflow passage, so that cooling performance is enhanced. [0016] According to the invention as set forth in claim 5, the combustion chambers and the valve chambers can be effectively cooled while adopting a compact shape, even in the case of a-two-cylinder internal combustion chamber. According to the present invention there is provided a cooling airflow passage structure for a cylinder head of an air-cooled type internal combustion engine, comprising a valve chamber at an upper portion of a combustion chamber, a cam chain chamber at a side portion of said combustion chamber, an exhaust port provided at a front portion of an area between said combustion chamber and said valve chamber, and an intake port provided at a rear portion of said area, characterized in that said exhaust port is placed away from said cam chain chamber, an area between said exhaust port and said cam chain chamber being made to be a front opening, said intake port is placed close to said cam chain chamber, the side opposite to said cam chain chamber of said intake port being made to be a rear opening, a front-rear direction cooling airflow passage is provided which connects said front opening and said rear opening to each other, and a sidewise cooling airflow passage is provided which branches off sideways from a roughly central portion of said front-rear direction cooling airflow passage and which is communicated with a side opening opened in a side surface of said cylinder head. [BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS] [Fig. 1] Fig. 1 is a side view showing the condition where an air-cooled type four-stroke-cycle internal combustion engine according to a first embodiment of the present invention is mounted on a frame of a motorcycle. [Fig. 2] Fig. 2 is a side view of a cylinder head 7 of the internal combustion engine 4. [Fig- 3] Fig. 3 is a sectional view along line Ill-Ill of Fig. 2, and is a horizontal sectional view of a lower portion of the cylinder head 7. [Fig. 4] Fig. 4 is a sectional view along line IV-IV of Fig. 3 . [Fig. 5] Fig. 5 is a sectional view along line V-V of Fig. 3 [Fig. 6] Fig. 6 is a sectional view along line VI-VI of Fig. 3 . [Fig. 7] Fig. 7 is a horizontal sectional view of running airflow passage portions in a cylinder head according to the second embodiment of the present invention. [Fig. 8] Fig. 8 is a horizontal sectional view of running airflow passage portions in a cylinder head according to the third embodiment of the present invention. [Fig. 9] Fig. 9 is a front view of the cylinder head according to the third embodiment. [Fig. 10] Fig. 10 is a horizontal sectional view of running airflow passage portions in a cylinder head for a two-cylinder internal combustion engine according to the fourth embodiment of the present invention. [Fig. 11] Fig. 11 is a horizontal sectional- view of running airflow passage portions in a cylinder head according to the fifth embodiment of the present invention. [Best Mode for Carrying out the Invention] [0017] Fig. 1 is a side view showing the condition where an air-cooled type four-stroke-cycle internal combustion engine according to the first embodiment of the present invention is mounted on a frame of a motorcycle. The frame includes a main frame 1 and an auxiliary frame 2 fixed to a head pipe 3 . The internal combustion engine 4 is suspended from the frames 1 and 2 through mount members. An outer shell of the internal combustion engine 4 includes a crankcase 5, a cylinder block 6, and a cylinder head 7.. A cylinder head cover mounted to. the front and rear sides of the cylinder head 7 is omitted in the figure. The internal combustion engine 4 includes an intake pipe 8 and an exhaust pipe 9. Symbol 19 denotes a spark plug. Arrow W indicates the direction of the running airflow. [0018] Fig. 2 is a side view of the cylinder head 7 of the internal combustion engine 4, in which arrow F indicates the front side of the internal combustion engine (this applies also to the other figures). In the state of being mounted on a vehicle, the internal combustion engine is mounted with its front side (direction F) slightly inclined downwards. The cylinder head -7 is provided on its outer circumference with a plurality of air-cooling fins 10. A combustion chamber 11 (indicated by broken line) is formed on the lower side of the cylinder head 7. The cylinder head 7 is provided with a spark plug screw engagement female screw hole 12 in a roughly central area of a lower portion thereof. A spark plug (not shown) is inserted skewly from the right side of the cylinder head 7 so that its tip end fronts on the combustion chamber 11, and is screw engaged. A valve chamber 13 is provided at an upper portion of the cylinder head 7, and side walls of the valve chamber 13 are provided with camshaft support holes 14, intake valve rocker arm shaft support holes 15, and exhaust valve rocker arm shaft support holes 16. The cylinder head cover (not shown) for covering the front and rear side of the valve chamber is mounted by use of cylinder head cover mount female screw holes 17 and 18. [0019] Fig. 3 is a sectional view along line Ill-Ill of Fig. 2, showing a horizontal section of a lower portion of the cylinder head 7. In the figure, broken line 7a is an outer circumferential line of a tubular portion of the cylinder head 7, and broken line lla is a circumferential edge line of the combustion chamber 11 provided on the lower side of the cylinder head. An intake port 20 communicated with the combustion chamber 11 and an intake valve guide hole 21 are provided in rear portions of the cylinder head 7, while an exhaust port 22 communicated with the combustion chamber 11 and an exhaust valve guide hole 23 are provided in front portions of the cylinder head 7. A valve seat 20a for an intake valve and a valve seat 22a for an exhaust valve are indicated by broken lines. An exhaust pipe 9 is connected to the exhaust port 22. The spark plug screw engagement female screw hole 12 is opened in a portion located between the intake port 20 and the exhaust port 22. Symbol 24 denotes a cooling fin for supporting the bottom surface of the valve chamber. A cam chain chamber 25 is provided in a left side portion of the cylinder block 6, and a cam chain (not shown) for transmitting power from a crankshaft (not shown) to a camshaft (not shown) is contained in the cam chain chamber 25. Symbols 26A, 26B, 26C, and 26D are insertion holes for stud bolts for connecting the crankcase 3, the cylinder block 6 and the cylinder head 7. [0020] A space provided with a front opening 30, a rear opening 31, and a side opening 32 is formed in the area surrounded by the outside wall of the exhaust port 22, the outside wall of the cam chain chamber 25, and the outside wall of the intake port 20. The space which connects the front opening 30 and the rear opening 31 to each other and through which the running airflow can blow in the roughly front-rear direction is referred to as a front-rear direction cooling airflow passage 33, though it is slightly inclined against the front-rear direction F. The space extending from a central portion of the front-rear direction cooling airflow passage 33 to the side opening 32 is a sidewise cooling airflow passage 34. The arrows indicated by bold broken lines in the figure are flow lines of the cooling airflow W generated by the running of the vehicle. When the spark plug is mounted in the spark plug screw engagement female screw hole 12, a shaft portion of the spark plug is exposed in the cooling airflow passage. A cooling airflow passage hollowed portion 35 is provided in the vicinity of the front side of the stud bolt insertion hole 26D. A branch flow of the cooling airflow having passed by the reinforcing rib 24 whirls in the cooling airflow passage hollowed portion 35, thereby cooling the surroundings of the stud bolt insertion hole 26D. [0021] Fig. 4 is a sectional view along line IV-IV of Fig. 3, and is a vertical sectional view along a section line crooked while passing the intake port 20 and the exhaust port 22. As shown in Fig. 3, the exhaust port 22 is deviated to the right side, and the intake port 20 to the left side, as viewed from a person facing forwards, but Fig. 4 shows these ports in a plane. In the figure, an upper half portion of the cylinder head 7 is occupied by the valve chamber 13, and a lower portion thereof is provided with the combustion chamber 11, the intake port 20, the valve seat 20a for the intake valve, the intake valve guide 21, the exhaust port 22, the valve seat 22a for the exhaust valve, and the exhaust valve guide 23. [0022] Fig. 5 is a sectional view along line V-V of Fig. 3. This figure is a vertical sectional view along the flow line of the cooling air W blowing by through the front-rear direction cooling airflow passage 33 shown in Fig. 3 in the front-rear direction, and intersects the section of Fig. 4. In the figure, the upper half portion of the cylinder head 7 is occupied by the valve chamber 13. A lower portion of the cylinder head 7 is provided with a bottom surface member 27 of the valve chamber 13 and a ceiling member 28 of the combustion chamber 11, and the reinforcing rib 24 is provided therebetween. The front -rear direction cooling airflow passage 33 extending from the front opening 30 to the rear opening 31 is formed between the bottom surface member 27 and the ceiling member 28. The arrow indicated by bold broken line in the figure is the flow line of the cooling airflow W which is generated by the running of the vehicle and which blows by from the front opening 30 to the rear opening 31. [0023] Fig. 6 is a sectional view along line VI-VI of Fig. 3, and a view of a sidewise section of the cylinder head 7 as viewed from the rear side. Arrow L indicates the left side, and arrow R indicates the right side. The cam chain chamber 25 is shown in a left side of the figure, the valve chamber 13 in an upper central area, the combustion chamber 11 in a lower area, the reinforcing rib 24 in a central area, and the side opening 32 in a right side area. The sidewise cooling airflow passage 34 is formed to extend from a portion near the reinforcing rib 24 toward the side opening 32. The arrow drawn in bold broken line in the figure indicates the flow line of the cooling airflow W branching off from the front-rear direction cooling airflow passage 33 and blowing by through the sidewise cooling airflow passage 34 toward the side opening 32. [0024] The first embodiment is configured as described above. This configuration is characterized in that, in the air-cooled type four-stroke-cycle internal combustion engine, in the area between the valve chamber and the combustion chamber, the exhaust port is provided at a position spaced from the cam chain chamber, the valve positions are at offset positions set off in the left-right directions, and the front-rear direction cooling airflow passage 33 and the sidewise cooling airflow passage 34 for the running airflow which are large in cross-sectional area are provided at central upper side of the combustion chamber. [0025] Fig. 7 is a horizontal sectional view of a running airflow passage portions in a cylinder head 40 according to the second embodiment of the present invention. In the following embodiments, the component parts having the same functions as those in the first embodiment will be denoted by the same symbols as those for the corresponding component parts in the first embodiment, and be described. This embodiment is characterized in that the cylinder head 7 in the first embodiment is provided with a secondary air supply device (not shown), a secondary air support port 41 communicated with the secondary air supply device is bored in a side wall of the exhaust port 22, and secondary air is supplied into the exhaust port 22 to oxidize HC and CO contained in the exhaust gas, for prevention of environmental pollution. The other points than the above-mentioned of the configuration are the same as in the first embodiment. [0026] As the secondary air supply device, there is used one of the air suction system in which supply air is directly taken in from the atmosphere through a check valve by utilizing the pulsation of the exhaust gas. In this system, air is taken in at the time when a negative pressure is fed to the position of the check valve. As the check vale, a reed valve composed of a thin steel sheet is used. The secondary air supply device is disposed in the vicinity of the exhaust port 22, so that it is brought to a high temperature. However, the secondary air supply device and the secondary air supply port 41 are cooled by the running airflow passing through the front-rear direction cooling airflow passage 33. [0027] Fig. 8 is a horizontal -sectional view of running airflow passage portions in a cylinder head 50 according to the third embodiment of the present invention, and Fig. 9 is a front view of the cylinder head 50. In this embodiment, a duct member 51 enlarged at a front portion thereof is provided at the front opening 30 of the cylinder head 7 in the first embodiment, and is fixed to the cylinder head 7 by a bolt 52. The running airflow can be collected from a wide range by the enlarged front portion of the duct member 51, and can be made to pass into running airflow passages 33 and 34. [0028] Fig. 10*is a horizontal sectional view of running airflow passages in a cylinder head 60 for a two-cylinder internal combustion engine according to the fourth embodiment of the present invention. The cylinder head 60 in this embodiment represents an example of the configuration of the running airflow passages shown in the first embodiment to a two-cylinder internal combustion engine. The cylinder head 60 has a structure in which the cylinder head 7 according to the first embodiment and a cylinder head configured by reversing the cylinder head 7 leftside right are integrally formed to be symmetrical, with a cam chain chamber 25 as a center of symmetry. Since the cam chain chamber 25 serving in common for the left and right cylinders is disposed at the center, the cylinder head as a whole is symmetrical on the left and right sides. Front openings 30 are provided at two positions in the cylinder head front surface, rear openings 31 are provided at two positions in the cylinder head rear surface, and side openings 32 are provided at one position in each of the left and right surfaces of the cylinder head. Left and right sets of cooling airflow passages 33, 34 are symmetrical with each other. [0029] Fig. 11 is a horizontal sectional view of running airflow passage portions in a cylinder head 70 according to the fifth embodiment of the present invention. In this embodiment, the cylinder head 7 (Fig. 3) in the first embodiment is improved, and a new rear opening 72 communicated with the position 71 corresponding to the cooling airflow passage hollowed portion 35 present in the first embodiment is provided between the stud bolt insertion hole 26D and the intake port 20. This ensures that the cooling airflow passage hollowed portion 35 which might cause stagnation of the cooling airflow in the first embodiment is eliminated, and the air present at the position 71 corresponding to the cooling airflow passage hollowed portion can be made to flow out smoothly, so that it is possible to enhance the cooling effect in the vicinity of the position 71 corresponding to the hollowed portion and in the vicinity of the stud bolt insertion hole 26D and the intake port 20. [0030] The cooling airflow passage structure for a cylinder head has been described referring to various embodiments above. In these embodiments, the following effects can be expected. (1) In the general configuration according to the prior art, the exhaust port 22 and the cam chain chamber 25 are adjacent to each other, so that air would not pass therebetween. According to the embodiments, the front- rear direction cooling airflow passage 33 for the running airflow is formed between the exhaust port 22 and the cam chain chamber 25, so that the exhaust port 22 which would be more raised in temperature than the intake port 20 can be effectively cooled from both the left and right sides. (2) Of the four bolts inserted in the stud bolt insertion holes 26A, 26B, 26C, 26D provided at four positions per one cylinder, particularly the stud bolt inserted in the stud bolt insertion hole 26A near the exhaust port 22 at a front portion and adjacent to the cam chain chamber 25 would easily be more raised in temperature than the other stud bolts, since the exhaust port and the cam chain chamber are adjacent to each other, in the general configuration according to the prior art. In each of the embodiments of the present invention, the stud bolt in concern is effectively cooled by the running airflow passing through the front-rear direction cooling airflow passage 33 formed in the area under consideration. This ensures that the four stud bolts are equalized in temperature, so that the facial pressure distribution in a gasket between the cylinder block 6 and the cylinder head 7 can be stabilized. (3) Since the smooth cooling airflow passages 33, 34 extending from a front portion of the cylinder head 7 to a rear portion and a side portion of the cylinder head 7 are provided in the manner of bridging over a central upper portion of the combustion chamber 11, the combustion chamber 11 can be cooled uniformly. This makes it possible to contrive an enhancement of combustion efficiency through an increase in compression ratio, restraint of emission of unburned materials, and restraint of knocking. (4) Since the shaft portion of the spark plug, the valve chamber bottom surface member 27, and the reinforcing member 24 are located in the cooling airflow passages 33, 34, these components are effectively cooled, and durability thereof is enhanced. The above-mentioned effects are obtained in common in all the embodiments of the present invention. (5) Second embodiment: The secondary air supply device and the secondary air supply port 41 disposed in the vicinity of the exhaust port 22 of the cylinder head are brought to a high temperature in the general configuration according to the prior art, but, in the cylinder head 40 according to this embodiment, they are cooled by the running airflow passing through the front- rear direction cooling airflow passage 33. (6) Third embodiment: The duct member 51 enlarged at a front portion thereof is provided at the front opening of the cooling airflow passage according to the present invention and is fixed to the cylinder head by the bolt 52. The running airflow can be collected from a wide range by the enlarged front portion of the duct member 51, and be made to flow into the running airflow passages 33, 34. (7) Fourth embodiment: It is shown that the cooling airflow passage structure according to the present invention can be applied also to a cylinder head for a two-cylinder internal combustion engine. (8) Fifth embodiment: The new rear opening 72 communicated with the position 71 corresponding to the cooling airflow passage hollowed portion 35 present in the first embodiment is provided between the stud bolt insertion hole 26D and the intake port 20. This makes it !. possible to eliminate the cooling airflow passage hollowed portion 35, to smoothen the flow of the cooling airflow, and to further enhance the cooling function. [Description of Reference Characters] [0032] 1: Main frame; 2: Auxiliary frame; 3: Head pipe ; 4: Internal combustion engine; 5: Crankcase; 6: Cylinder block; 7: Cylinder head; 7a: Outer circumferential line (broken line) of tubular portion of cylinder head; 8: intake pipe; 9: Exhaust pipe; 10: Air-cooling fin; 11: Combustion chamber; lla: Circumferential edge line (broken line) of combustion chamber; 12: Spark plug screw engagement female screw hole; 13: Valve chamber; 14: Camshaft support hole; 15: Intake valve rocker arm shaft support hole; 16: Exhaust valve rocker arm shaft support hole; 17: Cylinder head cover mount female screw hole; 18: Cylinder head' cover mount female screw hole; 19: Spark plug; 20: Intake port; 20a: Valve seat for intake valve; 21: Intake valve guide; 22: Exhaust port; 22a: Valve seat for exhaust valve; 23: Exhaust valve guide; 24: Cooling fin; 25: Cam chain chamber; 26A, 26B, 26C, 26D: Stud bolt insertion hole; 27: Valve chamber bottom surface member; 28: Combustion chamber ceiling member; 30: Front opening; 31: Rear opening; 32: Side opening; 33: Front-rear direction cooling airflow passage; 34: Sidewise cooling airflow passage; 35: Cooling airflow passage hollowed portion; 40: Cylinder head (second embodiment); 41: Secondary air supply port; 50: Cylinder head (third embodiment); 51: Duct member; 52: Bolt; 60: Cylinder head for two-cylinder internal combustion engine (fourth embodiment); 70: Cylinder head (fifth embodiment); 71: Position corresponding to cooling airflow passage hollowed portion; 72: Rear opening. communicated with a side opening in a side surface of a cylinder head. [Selected Drawing] Fig. 3 We Claim: 1. A cooling airflow passage structure for a cylinder head (7) of an air-cooled type internal combustion engine (4), comprising a valve chamber (13) at an upper portion of a combustion chamber (11), a cam chain chamber (25) at a side portion of said combustion chamber, an exhaust port (22) provided at a front portion of an area between said combustion chamber and said valve chamber, and an intake port (20) provided at a rear portion of said area, characterized in that said exhaust port (22) is placed away from said cam chain chamber (25), an area between said exhaust port and said cam chain chamber being made to be a front opening (30), said intake port (20) is placed close to said cam chain chamber (25), the side opposite to said cam chain chamber of said intake port (20) being made to be a rear opening (31), a front-rear direction cooling airflow passage (33) is provided which connects said front opening (30) and said rear opening (31) to each other, and a sidewise cooling airflow passage (34) is provided which branches off sideways from a roughly central portion of said front-rear direction cooling airflow passage (33) and which is communicated with a side opening (32) opened in a side surface of said cylinder head (7). 2. A cooling airflow passage structure for a cylinder head as claimed in claim 1, wherein a shaft portion of a spark plug (19) is exposed in said cooling airflow passage. 3. A cooling airflow passage structure for a cylinder head as claimed in claim 1, wherein a secondary air supply port (41) is provided to front on said cooling airflow passage. as 4. A cooling airflow passage structure for a cylinder head claimed in claim 1, wherein a duct member (51) enlarged in sectional area at a front portion thereof is provided at said front opening of said cooling airflow passage. 5. A cooling airflow passage structure for a cylinder head substantially as herein described with reference to the accompanying drawings.

Documents:

1708-del-2004-abstract.pdf

1708-del-2004-claims.pdf

1708-del-2004-correspondence-others.pdf

1708-del-2004-correspondence-po.pdf

1708-del-2004-description (complete).pdf

1708-del-2004-drawings.pdf

1708-del-2004-form-1.pdf

1708-del-2004-form-19.pdf

1708-del-2004-form-2.pdf

1708-del-2004-form-3.pdf

1708-del-2004-form-4.pdf

1708-del-2004-form-5.pdf

1708-del-2004-gpa.pdf

1708-del-2004-petetion-138.pdf