Cam bearing lubrication structure for internal combustion engine

Abstract

A cam bearing lubrication structure for an internal combustion engine includes a cylinder head having a cam bearing region, a plug hole for an ignition plug and a plug tube fitted liquid-tight therein. The cam bearing lubrication structure includes an outer periphery oil path bypassing along an outer peripheral face of the plug tube, a main lubricating oil passage extending through the plug hole and formed to connect to the outer periphery oil path and a guide passage formed in and through the cam bearing region to connect a sliding face of the cam bearing region from the outer periphery oil path and supplying lubricating oil to a sliding face of the cam bearing region and a camshaft. In addition, a lubricating oil supplying structure is provided for a valve apparatus for further increasing the oil supply amount to achieve a further increase in the speed of the engine.

Claims

1. A cam bearing lubrication structure for an internal combustion engine comprising: a cylinder head having a cam bearing region for supporting a camshaft for rotation; a plug hole in which an ignition plug supported on the cylinder head is accommodated such that an end thereof is exposed to a combustion chamber; a plug tube having a cylindrical shape and fitted liquid-tight at an upper end portion in the plug hole and fitted liquid-tight at a lower end portion in the plug hole to separate the inside of the cylinder head and the plug hole from each other, said plug tube extending continuously from the upper end portion in the plug hole to the lower end portion in the plug hole; an outer periphery oil path formed liquid-tight at the upper and lower end portions of the plug tube with respect to the plug hole and bypassing along an outer peripheral face of the plug tube from substantially the upper end portion in the plug hole to the lower end portion in the plug hole; a main lubricating oil passage extending through the plug hole in the cylinder head and formed for connecting to the outer periphery oil path; and a guide passage formed in and through the cam bearing region for connecting a sliding face of the cam bearing region from the outer periphery oil path and supplying lubricating oil to a sliding face of the cam bearing region and the camshaft; and a protuberance provided at a position below an upper end face of the plug tube and between the position below the upper end face and a position of an inlet of the guide passage in such a manner so as to protrude annularly from an outer periphery of the plug tube, said protuberance promotes the flow of lubricating oil supplied to and moving upwardly in the plug tube outer periphery oil path and into the inlet of the guide passage.

2. The cam bearing lubrication structure for the internal combustion engine according to claim 1, wherein an outlet of the guide passage to the cam bearing region is provided on a semicircular face at the plug hole side with respect to the center of rotation of the camshaft.

3. The cam bearing lubrication structure for the internal combustion engine according to claim 2, wherein the cam bearing region is configured from a plurality of divisional halves, and a threaded hole provided between the camshaft and the plug hole and used for a fastening member which couples the divisional halve is formed such that the guide passage extends therethrough, and the threaded hole is sealed by the fastening member.

4. The cam bearing lubrication structure for the internal combustion engine according to claim 3, wherein the cam bearing region is configured from divisional upper and lower halves, and the guide passage is formed by working in such a manner as to be inclined with respect to a mating plane of the upper and lower halves toward the plug hole.

5. The cam bearing lubrication structure for the internal combustion engine according to claim 1, wherein the cylinder head has a plurality of camshafts provided thereon sandwiching the plug hole therebetween, and a pair of guide passages are formed for each of the cam bearing regions.

6. The cam bearing lubrication structure for the internal combustion engine according to claim 2, wherein the cylinder head has a plurality of camshafts provided thereon sandwiching the plug hole therebetween, and a pair of guide passages are formed for each of the cam bearing regions.

7. The cam bearing lubrication structure for the internal combustion engine according to claim 3, wherein the cylinder head has a plurality of camshafts provided thereon sandwiching the plug hole therebetween, and a pair of guide passages are formed for each of the cam bearing regions.

8. The cam bearing lubrication structure for the internal combustion engine according to claim 4, wherein the cylinder head has a plurality of camshafts provided thereon sandwiching the plug hole therebetween, and a pair of guide passages are formed for each of the cam bearing regions.

9. The cam bearing lubrication structure for the internal combustion engine according to claim 1, wherein a holder unit is disposed at an upper end face of the upper end portion of the plug tube so as to closely contact with the upper end face to fix the plug tube from coming off from above with an annular seal member interposed therebetween.

10. The cam bearing lubrication structure for the internal combustion engine according to claim 9, wherein the cam bearing region is configured from upper and lower halves formed as upper and lower divisional portions, and the holder unit is configured integrally with the upper half.

11. A lubricating oil supplying structure for a valve apparatus of an internal combustion engine having a cylinder head which supports camshafts for rotation thereon, the lubricating oil supplying structure including: for each pair of engine valves for intake and exhaust, rocker arms supported at pivotally supporting base portions thereof for rocking motion by rocker arm shafts, the rocker arms being interposed between valve stem axial ends of the engine valves and cam faces of the camshafts to allow contact therebetween, pressing force from the cam faces acting upon the rocking arms and being transmitted to the valve stems to open and close the engine valves, the lubricating oil supplying structure for the valve apparatus of the internal combustion engine comprising: an oil passage provided in the cylinder head along an axial direction of the camshafts and formed from a single passage at a position lower than the rocker arm shafts between the engine valves, said oil passage being provided in a protuberance protruding from a lower face of a connecting bottom wall which interconnects lower portions of a pair of support walls which are provided on the cylinder head and support the opposite axial ends of the rocker arm shaft; and a pair of oil injection oil paths formed so as to be directed independently for the individual rocker arms from the oil passage.

12. The lubricating oil supplying structure for the valve apparatus according to claim 11, further comprising: valve stem pressing portions formed at locations at which the rocker arms contact with the valve stems side in a continuous relationship to lower faces of the rocking arms of the rocker arms; and the direction in which the oil injection oil paths are directed to the rocker arms being directed toward the lower faces of the rocking arms.

13. The lubricating oil supplying structure for the valve apparatus according to claim 12, wherein the lower face of the rocker arm is formed as a curved recessed portion being the lowest portion toward the valve stem pressing portion.

14. The lubricating oil supplying structure for the valve apparatus according to claim 13, wherein clearance adjustment members for adjusting gaps between the valve stem axial ends and the rocker arms are formed exchangeably as separate members between the valve stems and the valve stem pressing portions of the rocker arms.

15. The lubricating oil supplying structure for the valve apparatus according to claim 11, wherein the camshafts are configured independently as an intake camshaft and an exhaust camshaft and disposed at a position above the rocker arms, and sliding portions between the rocker arms and the cam faces are provided on upper faces of the rocker arms.

16. The lubricating oil supplying structure for the valve apparatus according to claim 15, wherein the rocker arm shafts are disposed between the intake and exhaust camshafts such that the sliding portions of the rocker arms are disposed to be directed outwardly relative to each other; the rocker arm shafts are disposed at heightwise positions different from each other with reference to an extension line of the cylinder center axis; and the oil passage is disposed in an offset relationship to the rocker arm shaft disposed at the higher position.

17. The lubricating oil supplying structure for the valve apparatus according to claim 16, wherein a cylinder of the internal combustion engine is mounted in an inclined relationship with respect to the vertical direction such that, in a state in which the internal combustion engine is mounted on a vehicle, a tip end of the rocker arm disposed on one of the two rocker arm shafts which is disposed at the higher position is directed obliquely upwardly while a tip end of the rocker arm disposed on the other one of the two rocker arm shafts which is disposed at the lower position is directed obliquely downwardly; the oil injection oil path is formed such that the injection direction from the oil injection oil path to the valve stem pressing portion of that one of the rocker arms in which the oil passage is disposed in an offset relationship is directed to the tip end of the rocker arm, and the oil injection oil path is formed such that the injection direction from the oil injection oil path to the valve stem pressing portion of the other rocker arm is directed to the pivotally supporting base portion of the rocker arm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

(2) FIG. 1 is a left side elevational view of an internal combustion engine of an embodiment of the present invention which includes a cam bearing lubrication structure for an internal combustion engine;

(3) FIG. 2 is a vertical sectional view of the internal combustion engine taken along a plane passing a center line of an intake valve and a center line of an exhaust valve;

(4) FIG. 3 is a vertical sectional view of the internal combustion engine taken along a plane passing a center line of a combustion plug tube;

(5) FIG. 4 is perspective view of the internal combustion engine with a head cover removed;

(6) FIG. 5 is an arrow view taken along line V-V in FIG. 3;

(7) FIG. 6 is a partial enlarged sectional view of FIG. 3;

(8) FIG. 7 is an arrow view taken along line VII-VII in FIG. 6;

(9) FIG. 8 is a partial enlarged sectional view of FIG. 3;

(10) FIG. 9 is a partial enlarged sectional view of FIG. 3;

(11) FIG. 10 is a vertical sectional view of the internal combustion engine taken along a plane passing a center line of an intake and exhaust valve;

(12) FIG. 11 is a partial enlarged sectional view of FIG. 10;

(13) FIG. 12 is a perspective view depicting the lubricating oil supplying structure for the valve apparatus; and

(14) FIG. 13 is a sectional view of the internal combustion engine taken along center axial lines of an intake rocker arm shaft and an exhaust rocker arm shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(15) In the following, a cam bearing lubrication structure and a lubricating oil supplying structure for a valve apparatus of an internal combustion engine according to an embodiment of the present invention depicted in FIGS. 1 to 9 is described. In the present embodiment, forward and rearward, upward and downward, and leftward and rightward directions signify the front and rear, up and down, and left and right of a vehicle body not depicted in which the internal combustion engine is incorporated.

(16) FIG. 1 is a side elevational view when an internal combustion engine 1 which includes a lubrication structure 60 for a cam bearing and a lubrication structure 70 for a valve apparatus of an embodiment of the present invention is viewed from the left. The internal combustion engine 1 includes a cylinder block 3, a cylinder head 4, and a head cover 5 stacked one on another on a crankcase 2 and fastened integrally by bolts not depicted. An oil pan 6 is fastened to a lower face of the crankcase 2 by bolts not depicted. The internal combustion engine 1 is a four-cylinder series type internal combustion engine wherein four cylinders 11 are formed in the leftward and rightward direction in the cylinder block 3. As depicted in FIGS. 2 to 4, a valve mechanism 30 of a four-valve system of the DOHC type which drives intake valves 18 and exhaust valves 19 to open and close is accommodated in a valve chamber 31 configured from the cylinder head 4 and the head cover 5.

(17) As depicted in FIG. 1, a crankshaft 10 is supported for rotation between the crankcase 2 and the cylinder block 3 such that it is directed in the leftward and rightward direction. As depicted in FIG. 2, a piston 12 is fitted in each of the cylinders 11 formed in the cylinder block 3 such that it slidably moves upwardly and downwardly. The piston 12 is connected to the crankshaft 10 through a connecting rod not depicted. A combustion chamber 13 configured from a recess is formed in the cylinder head 4 at a position opposing to a cylinder hole 11a of each cylinder 11. By explosion of fuel combusted in the combustion chamber 13, the piston 12 is slidably moved in the upward and downward directions in the cylinder 11, and the crankshaft 10 is driven to rotate by the upward and downward movement of the piston 12.

(18) For each combustion chamber 13, two inlets 14 and two outlets 15 are formed, and an intake port 16 for introducing intake air into the combustion chamber 13 and an exhaust port 17 for exhausting exhaust air generated in the combustion chamber 13 are communicated with the inlets 14 and the outlets 15, respectively. An intake valve 18 and an exhaust valve 19 for opening and closing the inlet 14 and the outlet 15 are supported for sliding movement by valve guides 20. The intake valves 18 and the exhaust valves 19 are normally biased in a valve closing direction by springs 23 fitted between upper retainers 21 fixed to an upper end of valve stems 18a and 19a and lower retainers 22 fixed to the cylinder head 4.

(19) As depicted in FIGS. 3 and 5 to 7, an ignition plug tube 25 is fitted at a position substantially centrally of the inlets 14 and the outlets 15 of one cylinder of the cylinder head 4. The ignition plug tube 25 is fitted in an ignition plug hole 24, and an ignition plug inserted in the ignition plug tube 25 is attached to the ignition plug hole 24.

(20) The ignition plug hole 24 is formed from a plurality of coaxial round holes having different inner diameters from each other as depicted in FIG. 6. A main plug hole 24a is formed downwardly from a mating plane 59 between an upper face of the cylinder head 4 and a camshaft holder 50. A plug tube fitting portion 24b is formed continuously to a lower portion of the main plug hole 24a. The plug tube fitting portion 24b has a rather small inner diameter, and an end portion 25a of the ignition plug tube 25 is inserted in the plug tube fitting portion 24b. An ignition plug abutting portion 24c having a smaller inner diameter is formed in a communicating relationship with a lower portion of the plug tube fitting portion 24b. A threaded portion 24d is formed in a communicating relationship with a lower portion of the ignition plug abutting portion 24c, and a threaded portion 26a of an ignition plug 26 is screwed with the threaded portion 24d. The threaded portion 26a is communicated at an end thereof with the combustion chamber 13.

(21) The ignition plug tube 25 is inserted in the ignition plug hole 24. The ignition plug tube 25 has a cylindrical shape, and a cylindrical intermediate portion 25c which occupies almost all of the ignition plug tube 25 has an outer diameter smaller than the inner diameter of the main plug hole 24a of the ignition plug hole 24. A flange portion 25d is provided at the upper end portion 25a of the ignition plug tube 25 and is formed with a diameter greater than the inner diameter of the main plug hole 24a. A lower end portion 25b of the ignition plug tube 25 is fitted in the plug tube fitting portion 24b of the ignition plug hole 24, and a grooved portion 25f is formed at the lower end portion 25b such that an annular seal member 27 is fitted into the grooved portion 25f.

(22) The ignition plug tube 25 is fixed by the camshaft holder 50 hereinafter described so that it does not come off upwardly. An abutting portion 50a is formed on the camshaft holder 50 such that it is abutted with the flange portion of the ignition plug tube 25. A grooved portion 50b is formed at the abutting portion 50a such that an annular seal member 28 is fitted therein. Further, a plug hole 50c is formed on the camshaft holder 50 such that it communicates with the inside of the ignition plug tube 25 and an ignition plug is inserted in the plug hole 50c.

(23) The ignition plug tube 25 is inserted in the ignition plug hole 24 in a state in which the annular seal member 27 is fitted in the grooved portion 25f of the lower end portion 25b and is fixed from coming off from above by the camshaft holder 50 having the grooved portion 50b in which the annular seal member 28 is fitted. When the ignition plug tube 25 is fixed, a space (plug tube outer periphery oil path 63 hereinafter described) configured from an inner circumferential face of the ignition plug hole 24 and an outer circumferential face of the ignition plug tube 25 is held liquid-tight at the upper end portion 25a and the lower end portion 25b of the ignition plug tube 25 by the annular seal members 27 and 28. Thus, the inside of the cylinder head 4 and the ignition plug hole 24 are partitioned by the ignition plug tube 25

(24) After the ignition plug tube 25 is fixed from coming off the cylinder head 4 by the camshaft holder 50, the ignition plug 26 is inserted into the ignition plug tube 25 through the plug hole 50c of the camshaft holder 50. Then, the threaded portion 26a formed at an end of the ignition plug 26 is screwed into the threaded portion 24d of the ignition plug hole 24 and attached such that an electrode portion 26b of the ignition plug 26 is exposed to the combustion chamber 13.

(25) In the valve chamber 31, an intake camshaft 32 and an exhaust camshaft 33 are disposed in parallel to each other in the forward and rearward direction in such a manner that they are directed in the leftward and rightward direction of the internal combustion engine 1 and sandwich the ignition plug hole 24 therebetween. The intake camshaft 32 and the exhaust camshaft 33 are each supported by a cam bearing 38, which is configured from a lower bearing region 38b as a bearing half formed on the cylinder head 4 and an upper bearing region 38a as another bearing half formed on the camshaft holder 50.

(26) As depicted in FIGS. 3 and 4, for each ignition plug hole 24, two front bolt threaded holes 53 and two rear bolt threaded holes 54 are disposed on the cylinder head 4. The bolt threaded holes 53 and the bolt threaded holes 54 are formed at positions sandwiching the lower bearing region 38b. On the camshaft holder 50, two front bolt insertion holes 51 and two rear bolt insertion holes 52 are disposed for the ignition plug hole 24 corresponding to the bolt threaded holes 53 and 54 formed in the cylinder head. The bolt insertion holes 51 and the bolt insertion holes 52 are formed at positions sandwiching the upper bearing region 38a.

(27) As depicted in FIG. 8, tubular member insertion holes 51a and 53a are formed at a lower portion of the bolt insertion hole 51 and an upper portion of the bolt threaded hole 53 on the intake camshaft 32 side and have an inner diameter a little greater than the inner diameters of them. A tubular member 58 is fitted in the tubular member insertion holes 51a and 53a and formed such that a flange bolt 55 is fitted therein.

(28) The ignition plug tubes 25 are inserted into the ignition plug holes 24 formed on the cylinder head 4, and the intake camshaft and the exhaust camshaft are placed at predetermined positions on the lower bearing region 38b formed on the cylinder head. Thereafter, the camshaft holder 50 is fitted in such a manner so as to sandwich the intake camshaft and the exhaust camshaft. The flange bolts 55 and 56 are fitted into the bolt insertion holes 51 and 52 of annular seal members 57 and the camshaft holder 50. Then, the flange bolts 55 and 56 are screwed into the bolt threaded holes 53 and 54 of the cylinder head 4 to fasten the camshaft holder 50 integrally to the cylinder head 4 while the intake camshaft 32 and the exhaust camshaft 33 are supported for rotation on the cam bearings 38. Since the annular seal members 57 are interposed between the flange bolts 55 and 56 and the camshaft holder 50, the inside of the bolt insertion holes 51 and 52 and the inside of the bolt threaded holes 53 and 54 are formed liquid-tight.

(29) As depicted in FIG. 4, a driven sprocket wheel 41 is integrally attached to a right end portion of the intake camshaft 32, and an endless timing chain 42 extends between and around the driven sprocket wheel 41 and a driving sprocket wheel 40 provided on the crankshaft 10. Consequently, the intake camshaft 32 is rotated by rotational driving force of the crankshaft 10.

(30) An intake cam gear 36 is attached at a substantially central portion of the intake camshaft 32 in the rightward direction such that the intake cam gear 36 rotates integrally with the intake camshaft 32. An exhaust cam gear 37 is attached integrally on the exhaust camshaft 33 such that it meshes with the intake cam gear 36. The intake cam gear 36 and the exhaust cam gear 37 have a number of teeth equal to each other. Consequently, the rotational driving force of the intake camshaft 32 which is driven to rotate by the crankshaft 10 is transmitted to the exhaust camshaft 33 through intake cams 34 and exhaust cams 35 so that the exhaust camshaft 33 is driven to rotate at the same rotational speed but in the opposite direction of rotation of the intake cam shaft 32.

(31) As depicted in FIG. 2, an intake rocker arm 43 and an exhaust rocker arm 44 are supported for rocking motion on the cylinder head 4 by rocker arm shafts 45 extending in parallel to the intake and exhaust camshafts 32 and 33. Cam abutting portions 43b and 44b on an upper face at an end of the portions 43a and 44a of the intake and exhaust rocker arms 43 and 44 are abutted by cam faces 34a and 35a of the intake and exhaust cams 34 and 35, respectively. Consequently, valve shaft side abutting portions 43c and 44c on a lower face of an end of the arm portions 43a and 44a press the valve stems 18a and 19a of the intake and exhaust valves 18 and 19 through clearance adjustment members 29.

(32) If the internal combustion engine 1 starts operation and the intake and exhaust camshafts 32 and 33 are rotated by rotational driving force transmitted from the crankshaft 10, then the intake and exhaust cams 34 and 35 are rotated. Consequently, the cam abutting portions 43b and 44b of the intake and exhaust rocker arms 43 and 44 are pressed in accordance with the shape of the intake and exhaust cam faces 34a and 35a of the intake and exhaust cams 34 and 35 to rock the intake and exhaust rocker arms 43 and 44. Consequently, the valve shaft side abutting portions 43c and 44c press the valve stems 18a and 19a of the intake and exhaust valves 18 and 19 through the clearance adjustment members 29 to operate the intake valves 18 and the exhaust valves 19 to open and close at a predetermined timing with a predetermined lift amount.

(33) As depicted in FIG. 1, hereinafter a cam bearing lubrication structure 60 which supplies lubricating oil to the cam bearings 38 is described. An oil pump 7 is provided in the crankcase 2 and is driven by power of the crankshaft 10. A strainer 8 is disposed in the oil pan 6 and connected to the oil pump 7. Consequently, if the oil pump 7 is driven by the crankshaft 10, then the lubricating oil reserved in the oil pan 6 is sucked in from the strainer 8 and fed from the oil pump 7 to different locations of the internal combustion engine 1 through a supply oil path 9.

(34) The lubricating oil pressure fed from the oil pump 7 passes a supply oil path 9a, which extends to the mating plane between the crankcase 2 and the cylinder block 3 upwardly from the crankshaft 10 and passes a supply oil path 9b formed along the mating plane between the crankcase 2 and the cylinder block 3 toward the front of the cylinder block 3. Thereafter, the lubricating oil passes a supply oil path 9c formed in the cylinder head 4 from the cylinder block 3 obliquely upwardly from a front end portion of the supply oil path 9b, and is fed to a main lubricating oil passage 62 formed so as to be directed in the leftward and rightward direction in the cylinder head 4 as depicted in FIG. 5. A right end 62a of the main lubricating oil passage 62 is connected to the supply oil path 9c, and a left end 62b of the main lubricating oil passage 62 is close by a plug 67. As depicted in FIGS. 3 and 5, the main lubricating oil passage 62 is formed such that it extends through the four ignition plug holes 24 formed in the cylinder head 4.

(35) As depicted in FIGS. 6 and 7, the plug tube 25 is inserted in the ignition plug hole 24. The plug tube outer periphery oil path 63 as a space configured from the inner circumferential face of the ignition plug hole 24 and the outer circumferential face of the ignition plug tube 25 is held liquid-tight at the upper end portion 25a and the lower end portion 25b of the ignition plug tube 25 by the annular seal members 27 and 28. Consequently, the inner side of the cylinder head 4 and the ignition plug hole 24 are partitioned by the ignition plug tube 25. As depicted in FIG. 7, the ignition plug hole 24 is in communication with the main lubricating oil passage 62. Therefore, the lubricating oil flowing along the main lubricating oil passage 62 on the upstream side flows into the plug tube outer periphery oil path 63 from an inlet 63a of the plug tube outer periphery oil path 63 and bypasses along the outer circumferential face of the ignition plug tube 25 and then flows out into the main lubricating oil passage 62 on the downstream side from an outlet 63b of the plug tube outer periphery oil path 63.

(36) As depicted in FIGS. 3, 6, 8, and 9, a guide passage 64 is formed so as to extend from the plug tube outer periphery oil path 63 through the lower bearing region 38b formed in the cylinder head 4 toward the ignition plug hole 24 in an inclined relationship to the mating plane 59 between the camshaft holder 50 and the cylinder head 4. The guide passage 64 connects to sliding faces of the intake camshaft 32 and the bearing 38 and between the exhaust camshaft 33 and the bearing 38. An inlet 64a of the guide passage 64 is in communication with the plug tube outer periphery oil path 63. An outlet 64b to the cam bearing region 38 is provided on a semicircular face 38c at the ignition plug hole 24 side with respect to the center of rotation of the intake and exhaust camshafts 32 and 33.

(37) As depicted in FIG. 6, a protuberance 25g is formed on the ignition plug tube 25 such that it protrudes annularly from an outer circumferential face of the intermediate portion 25c. The protuberance 25g is positioned above the inlets 64a of the guide passage 64 communicating with the plug tube outer periphery oil path 63 and below the upper end portion 25a of the ignition plug tube 25. The protuberance 25g promotes the flow of lubricating oil supplied to and going upwardly in the plug tube outer periphery oil path 63 into the inlet 64a of the guide passage 64.

(38) As depicted in FIGS. 8 and 9, the guide passage 64 is formed so as to extend through the bolt threaded hole 53 provided between the ignition plug hole 24 and the intake camshaft 32 or exhaust camshaft 33. The guide passage 64 is sealed by the flange bolt 55 or 56 screwed in the bolt threaded hole 53 and the annular seal member 57 so that the lubricating oil may not leak from the guide passage 64.

(39) In the cam bearing lubrication structure 60 of the present embodiment, lubricating oil fed from the oil pump 7 passes the supply oil path 9 as depicted in FIG. 1 and is fed from the supply oil path 9 to the right end 62a of the main lubricating oil passage 62 and is further fed from the right end 62a successively to the plug tube outer periphery oil paths 63 provided in the cylinders as depicted in FIG. 5. Furthermore, as depicted in FIGS. 8 and 9, the lubricating oil flows from the plug tube outer periphery oil path 63 into the guide passage 64, passes the bolt threaded hole 53, flows out and is supplied from the outlet 64b formed on the semicircular face 38c at the plug side of the cam bearing 38 to the sliding faces of the cam bearing 38 and the intake and exhaust camshafts 32 and 33. As depicted in FIG. 8, the mating plane between the upper bearing region 38a and the lower bearing region 38b at the intake camshaft 32 side, namely, the mating plane 59 between the cylinder head 4 and the camshaft holder 50, is inclined to the ignition plug hole 24 side. Consequently, although the lubricating oil flowing from the outlet 64b into the cam bearing 38 is directed downwardly through the mating plane 59, it is blocked from flowing into the bolt insertion hole 51 and the bolt threaded hole 53 by the tubular member 58 fitted in the bolt insertion hole 51 and the bolt threaded hole 53. Thus, sufficient lubricating oil can be fed to the cam bearing 38.

(40) The cam bearing lubrication structure 60 of the internal combustion engine 1 of the embodiment of the present invention is configured in such a manner as described above. Therefore, the upper and lower end portions 25a and 25b of the ignition plug tube 25 are fitted liquid-tight in the ignition plug hole 24 to form the plug tube outer periphery oil path 63 and the guide passage 64 is formed from the plug tube outer periphery oil path 63 in such a manner so as to connect the cam bearing region 38. Consequently, lubricating oil is directly supplied from the plug tube outer periphery oil path 63 to the cam bearing region 38 through the guide passage 64. Consequently, the lubricating oil passage to the cam bearing region 38 can be reduced in length, and as a result, it is possible to reduce the size of the cylinder head 4 to achieve miniaturization of the internal combustion engine 1.

(41) Further, the inlet 63a of the guide passage 64 from the plug tube outer periphery oil path 63 is provided on the semicircular face 38c of the cam bearing region 38 at the ignition plug hole 24 side. Therefore, it is possible to reduce the length of the guide passage 64 to the utmost and reduce the time for oil supply to the cam bearing region 38 after the internal combustion engine 1 is started up.

(42) Further, the guide passage 64 is formed so as to extend through the bolt threaded hole 53 between the intake and exhaust camshafts 32 and 33 and the ignition plug hole 24, and the guide passage 64 is sealed by the flange bolt 55. Therefore, in comparison with an alternative case in which the guide passage 64 is formed bypassing the bolt threaded hole 53, the guide passage 64 can be connected in the shortest distance. Thus, it is possible to achieve a space saving and further reduce the working cost.

(43) Furthermore, the cam bearing 38 is formed from upper and lower halves of the upper bearing region 38a and the lower bearing region 38b, and the guide passage 64 is formed by working in an inclined relationship with respect to the mating plane 59 of the upper bearing region 38a and the lower bearing region 38b so as to be directed to the ignition plug hole 24. Therefore, when the upper and lower cam bearing regions 38a and 38b formed as two divisional upper and lower portions of the guide passage 64, the working procedure can be carried out readily by working the upper and lower cam bearing regions 38a and 38b obliquely.

(44) Further, the cylinder head 4 is configured such that the plurality of intake and exhaust camshafts 32 and 33 are provided sandwiching the ignition plug hole 24 therebetween and the guide passages 64 are provided in a pair for each of the cam bearings 38. Therefore, the supply of lubricating oil to the cam bearings 38 at the opposite sides of the ignition plug hole 24 can be carried out from the plug tube outer periphery oil path 63 of the common ignition plug hole 24. Thus, the oil supply can be simplified.

(45) The protuberance 25g is provided at a position below the upper end portion 25a of the ignition plug tube 25 between the position and the position of the inlet 64a of the guide passage 64 such that it protrudes annularly from the outer periphery of the ignition plug tube 25. Therefore, the flow of lubricating oil, which has flowed from below into and flowed upwardly in the plug tube outer periphery oil path 63 into the inlet 64a of the guide passage 64, can be promoted to facilitate the supply of the lubricating oil into the guide passage 64.

(46) The camshaft holder 50 is attached in such a manner so as to press down an upper end face 25e of the ignition plug tube 25, which configures part of the plug tube outer periphery oil path 63, through the annular seal member 28. Therefore, the ignition plug tube 25 which is acted upon by hydraulic pressure and is likely to come off can be suppressed with certainty.

(47) The cam bearing region is configured from the upper and lower halves formed as upward and downward divisional portions, and the holder unit is configured integrally with the upper half. When the holder unit is provided, by forming the holder unit integrally with the upper half of the cam bearing region, a reduction in the number of parts can be anticipated.

(48) As depicted in FIG. 10, an intake rocker arm 143 and an exhaust rocker arm 144 are supported for rocking motion on the cylinder head 104 by intake rocker arm shafts 145 and exhaust rocker arm shafts 146.

(49) As depicted in FIGS. 10, 11 and 12, the intake and exhaust rocker arms 143 and 144 include pivotally supporting base portions 143a and 144a supported for pivotal motion around the intake and exhaust rocker arm shafts 145 and 146 extending therethrough, and rocking arms 143b and 144b extending from the pivotally supporting base portions 143a and 144a, respectively. Valve stem pressing portions 143f and 144f are formed on the intake and exhaust rocker arms 143 and 144 in a continuing relationship to lower faces 143d and 144d of the rocking arms 143b and 144b and press the valve stems 118a and 119a of the intake and exhaust valves 118 and 119, respectively. Further, curved recessed portions 143g and 144g are formed toward the valve stem pressing portions 143f and 144f on the lower faces 143d and 144d of the intake and exhaust rocker arms 143 and 144, respectively. When the internal combustion engine is mounted on a vehicle not depicted, the curved recessed portion 144g of the exhaust rocker arm 144 is positioned at the lowest position.

(50) Sliding portions 143e and 144e are provided on upper faces 143c and 144c of the intake and exhaust rocker arms 143 and 144 so as to contact with the cam faces 134a and 135a of the intake and exhaust cams 134 and 135, respectively. Exchangeable clearance adjustment members 129 are formed as separate members from and fitted in the upper retainers 121 of the intake and exhaust valves 118 and 119 and are used to adjust the gaps between valve stem axial ends 118c and 119c and the intake and exhaust rocker arms 143 and 144, respectively. The intake and exhaust rocker arms 143 and 144 are interposed between the valve stem axial ends 118c and 119c of the intake and exhaust valves 118 and 119 and the cam faces 134a and 135a of the intake and exhaust cams 134 and 135, respectively. The sliding portions 143e and 144e of the intake and exhaust rocker arms 143 and 144 contact with the cam faces 134a and 135a to cause the valve stem pressing portions 143f and 144f to press the valve stem axial ends 118c and 119c through the clearance adjustment members 129, respectively.

(51) As depicted in FIGS. 10, 11, 12 and 13, support walls 171 and 172 which support opposite axial end portion 145a and 145b of the rocker arm shafts 145 are formed on the cylinder head 104 and support the intake and exhaust rocker arms 143 and 144 for rocking motion thereon. The support wall 171 is provided so as to be positioned at a central position of each cylinder in the leftward and rightward direction. The ignition plug hole 124 is perforated at a central position of the support wall 171 in the leftward and rightward direction. The support walls 172 are formed in a pair on the left and right of the support wall 171. The support wall 171 and the support walls 172 are connected at lower portions thereof by a connecting bottom wall 173. A protuberance 174 is formed on a lower face 173a of the connecting bottom wall 173 and protrudes downwardly.

(52) As depicted in FIG. 13, rocker arm shaft fitting holes 171a and 172a are provided in a leftward and rightward direction in the support walls 171 and 172 so that the intake and exhaust rocker arm shafts 145 and 146 are inserted into the rocker arm shaft fitting holes 171a and 172a. The rocker arm shaft fitting hole 171a of the support wall 171 is in communication with the ignition plug hole 124.

(53) After the intake and exhaust rocker arms 143 and 144 are inserted between the support wall 171 and the support walls 172, the intake and exhaust rocker arms 143 and 144 are inserted from the rocker arm shaft fitting holes 172a of the support walls 172. Further, the intake and exhaust rocker arms 143 and 144 are fitted into pivotally supporting holes 143h and 144h formed in the pivotally supporting base portions 143a and 144a of the intake and exhaust rocker arms 143 and 144, respectively, and then inserted into the rocker arm shaft fitting hole 171a of the support wall 171. Consequently, the intake and exhaust rocker arms 143 and 144 are supported by the support walls 171 and 172.

(54) As depicted in FIG. 11, the intake and exhaust rocker arms 143 and 144 are disposed such that the sliding portions 143e and 144e thereof are directed outwardly and disposed so as to be positioned between the intake and exhaust camshafts 132 and 133 in the forward and rearward direction.

(55) The intake rocker arm shaft 145 and the exhaust rocker arm shaft 146 are disposed at heightwise positions different from each other with reference to an extension line L of a cylinder center axis. The cylinder 111 of the internal combustion engine is mounted in an inclined relationship with respect to the vertical direction in a state in which the internal combustion engine is mounted on a vehicle not depicted. A tip end of the intake rocker arm 143 on which one of the intake rocker arm shaft 145 and the exhaust rocker arm shaft 146 which is disposed at a higher position is directed obliquely upwardly and a tip end of the exhaust rocker arm 144 of the other one disposed at a lower position is directed obliquely downwardly.

(56) An engaging hole 172b is formed in the support walls 172 into which an engaging member 168 is screwed for preventing the intake and exhaust rocker arm shafts 145 and 146 from coming off. The engaging member 168 has a male thread (not depicted) formed at a tip end thereof and is screwed with a female thread (not depicted) formed in the engaging hole 172b. This engaging member 168 engages with an engaging recessed portion 145a of the intake rocker arm shaft 145 and an engaging recessed portion 146a of the exhaust rocker arm shaft 146 so that coming off of the intake and exhaust rocker arm shafts 145 and 146 from the cylinder head 104 is prevented by the engaging members 168. It is to be noted that a hole having a cross section of a regular hexagonal shape is formed at a head portion of the engaging member 168 such that the engaging member 168 can be screwed by inserting a tip end portion of a tool not depicted which has a regular hexagonal shape into the hole.

(57) If the internal combustion engine starts operation and the intake and exhaust camshafts 132 and 133 are rotated by rotational driving force transmitted from the crankshaft, then the intake and exhaust cams 134 and 135 are rotated. Consequently, the cam abutting portions 143b and 144b of the intake and exhaust rocker arms 143 and 144 are pressed in accordance with the shape of the intake and exhaust cam faces 34a and 35a of the intake and exhaust cams 134 and 135 to rock the intake and exhaust rocker arms 143 and 144. Consequently, the valve stem abutting portions 143c and 144c press the valve stems 118a and 119a of the intake and exhaust valves 118 and 119 through the clearance adjustment members 129 to operate the intake valves 118 and the exhaust valves 119 to open and close at a predetermined timing with a predetermined lift amount.

(58) Hereinafter, a cam bearing lubrication structure which supplies lubricating oil to the cam bearings 138 of the internal combustion engine and a lubricating oil supplying structure to the valve apparatus 130 are described. As depicted in FIG. 1, an oil pump 7 is provided in the crankcase 2 and is driven by power from the crankshaft 10. A strainer 8 is disposed in the oil pan 6 and connected to the oil pump 7. Consequently, if the oil pump 7 is driven by the crankshaft 10, then the lubricating oil reserved in the oil pan 6 is sucked in from the strainer 8 and fed from the oil pump 7 to different locations of the internal combustion engine 1 through a supply oil path 9.

(59) The lubricating oil pressure fed from the oil pump 7 passes a supply oil path 9a, that extends to the mating plane between the crankcase 2 and the cylinder block 3 upwardly from the crankshaft 10 and passes a supply oil path 9b formed along the mating plane between the crankcase 2 and the cylinder block 3 toward the front of the cylinder block 3. Thereafter, the lubricating oil passes a supply oil path 9c formed in the cylinder head 4 from the cylinder block 3 obliquely upwardly from a front end portion of the supply oil path 9b, and is fed to a main lubricating oil passage 62 formed so as to be directed in the leftward and rightward direction in the cylinder head 4 as depicted in FIG. 5.

(60) As depicted in FIG. 10, the main lubricating oil passage 162 is formed from a single passage at a position below the intake rocker arm shaft 145 and the exhaust rocker arm shaft 46 between the intake valve 118 and the exhaust valve 119. The main lubricating oil passage 162 is formed in the protuberance 174 protruding downwardly from the connecting bottom wall 173 by which lower portions of the support wall 171 and the support walls 172 are connected to each other.

(61) As depicted in FIG. 5, a right end 62a of the main lubricating oil passage 62 is connected to the supply oil path 9c, and a left end 62b of the main lubricating oil passage 62 is closed by a plug 67. As depicted in FIGS. 3 and 5, the main lubricating oil passage 62 is formed such that it extends through the four ignition plug holes 24 formed in the cylinder head 4.

(62) As depicted in FIGS. 3 and 6, a guide passage 64 is formed so as to extend from the plug tube outer periphery oil path 63 through the lower bearing region 38b formed in the cylinder head 4 toward the ignition plug hole 24 in an inclined relationship to the mating plane 59 between the camshaft holder 50 and the cylinder head 4. The guide passage 64 connects to sliding faces of the intake camshaft 32 and the bearing 38 and between the exhaust camshaft 33 and the bearing 38. An inlet 64a of the guide passage 64 is in communication with the plug tube outer periphery oil path 63, and an outlet 64b to the cam bearing region 38 is provided on a semicircular face 38c at the ignition plug hole 24 side with respect to the center of rotation of the intake and exhaust camshafts 32 and 33.

(63) As depicted in FIGS. 3 and 6, the guide passage 64 is formed so as to extend through the bolt threaded hole 53 provided between the ignition plug hole 24 and the intake camshaft 32 or exhaust camshaft 33. The guide passage 64 is sealed by the flange bolt 55 or 56 screwed in the bolt threaded hole 53 and the annular seal member 57 so that the lubricating oil may not leak from the guide passage 64.

(64) As depicted in FIGS. 11 and 12, the main lubricating oil passage 162 is formed in the protuberance 174 of the connecting bottom wall 173 by which the lower portions of the paired support walls 171 and 172, which support the opposite axial ends of the intake and exhaust rocker arm shafts 45 and 46, are connected to each other. The main lubricating oil passage 162 is disposed in an offset relationship to the intake rocker arm shaft 145 disposed at the higher position with reference to the extension line L of the cylinder center axis. Further, an intake side oil injection oil path 175 and an exhaust side oil injection oil path 176 are formed in a paired relationship with each other such that they are directed independently for each of the intake rocker arms 143 and each of the exhaust rocker arms 144, respectively, from the main lubricating oil passage 162. The intake side oil injection oil path 175 and the exhaust side oil injection oil path 176 are open in the valve chamber 131 at an intake side oil injection point 177 and an exhaust side oil injection point 178, respectively.

(65) The intake side oil injection oil path 175 is formed such that lubricating oil injected from the intake side oil injection point 177 toward the intake rocker arm 143 is directed to a tip end of the intake rocker arm 143 on the lower face 143d of the rocking arm 143b of the intake rocker arm 143. Thus, the lubricating oil injected from the intake side oil injection point 177 of the intake side oil injection oil path 175 is supplied to the valve stem pressing portion 143f of the intake rocker arm 143.

(66) Meanwhile, the exhaust side oil injection oil path 176 is formed such that lubricating oil injected from the exhaust side oil injection point 178 toward the exhaust rocker arm 144 is directed to the pivotally supporting base portion 144a of the exhaust rocker arm 144 on the lower face 144d of the rocking arm 144b of the exhaust rocker arm 144. Thus, the lubricating oil injected from the exhaust side oil injection point 178 of the exhaust side oil injection oil path 176 is injected to the pivotally supporting base portion 144a of the exhaust rocker arm 144 and is supplied to the valve stem pressing portion 144f along the lower face 144d of the rocking arm 144b.

(67) As depicted in FIG. 13, rocker shaft oil passages 145b and 146b are perforated in the intake and exhaust rocker arm shafts 145 and 146 so as to be directed in the longitudinal direction from the faces of the intake and exhaust rocker arm shafts 145 and 146 at the support wall 171 side, respectively. Further, the bearing oil supplying passages 145c and 146c are perforated so as to be communicated with the pivotally supporting holes 143h and 144h of the intake and exhaust rocker arms 143 and 144, respectively. The rocker shaft oil passages 145b and 146b are communicated with a plug outer periphery oil path 163 configured between the above-described ignition plug hole 124 and the ignition plug tube 125.

(68) In the cam bearing lubrication structure 60 of the present embodiment, if the internal combustion engine 1 is started up and the oil pump 7 begins to feed lubricating oil, then the lubricating oil passes the supply oil path 9 as depicted in FIG. 1 and is fed from the supply oil path 9 to the right end 62a of the main lubricating oil passage 62 as depicted in FIG. 5. Then, the lubricating oil is successively fed from the right end 62a to the main lubricating oil passage 62 provided in each cylinder through the plug outer periphery oil path 63 provided in each cylinder.

(69) The lubricating oil fed to the main lubricating oil passage 62 passes the intake side oil injection oil path 75 and is injected from the intake side oil injection point 77 toward the tip end of the intake rocker arm 43 on the lower face 43d of the rocking arm 43b of the intake rocker arm 43 so that it is supplied to the valve stem pressing portion 43f of the intake rocker arm 43. Further, the lubricating oil passes the exhaust side oil injection oil path 76 and is injected from the exhaust side oil injection point 78 toward the pivotally supporting base portion 44a of the exhaust rocker arm 44 on the lower face 44d of the rocking arm 44b of the exhaust rocker arm 44. Thereafter, the lubricating oil flows along the lower face 44d of the rocking arm 44b and is supplied downwardly to the valve stem pressing portion 44f from the curved recessed portion 44g.

(70) Furthermore, the lubricating oil fed to the main lubricating oil passage 62 enters the rocker shaft oil passages 45b and 46b formed in the intake and exhaust rocker arm shafts 45 and 46 and is supplied from the bearing oil supplying passages 45c and 46c to sliding faces of the intake and exhaust rocker arm shafts 45 and 46 and the pivotally supporting holes 43h and 44h of the pivotally supporting base portions 43a and 44a of the intake and exhaust rocker arms, respectively.

(71) The lubricating oil supplying structure 70 for the valve apparatus of the internal combustion engine 1 of the embodiment of the present invention is configured in such a manner as described above. Therefore, the main lubricating oil passage 62 is formed from a single passage extending along the intake and exhaust camshafts 32 and 33 at a position lower than the intake and exhaust rocker arm shafts 45 and 46 between the intake and exhaust valves 18 and 19, and the paired oil injection oil paths directed independently for each of the intake and exhaust rocker arms 43 and 44 from the main lubricating oil passage 62 are provided. Therefore, while the path for the injection oil is reduced in length, oil is supplied from the single intake side oil injection oil path 75 and the single exhaust side oil injection oil path 76 directly to the intake and exhaust rocker arms 43 and 44. Oil to be supplied to the intake side oil injection oil paths 75 and the exhaust side oil injection oil paths 76 is supplied from the common oil passage. Consequently, it is possible to assure the amount of oil that is supplied. Further, since the intake side oil injection oil paths 75 and the exhaust side oil injection oil paths 76 are provided from the single main lubricating oil passage 62, a space saving of the lubricating oil supplying structure 70 in the valve apparatus can be anticipated and the fabrication cost can be reduced.

(72) Furthermore, the lower faces 43d and 44d of the rocking arms 43b and 44b of the intake and exhaust rocker arms 43 and 44 are formed continuously to the valve stem pressing portions 43f and 44f. In addition, the intake and exhaust side oil injection oil paths 75 and 76 directed to the intake and exhaust rocker arms 43 and 44 are formed such that they are directed to the lower faces 43d and 44d of the rocking arms 43b and 44b, respectively. Consequently, even if part of the injected oil does not directly reach the valve stem pressing portions 43f and 44f, it flows along the lower faces 43d and 44d of the rocking arms 43b and 44b and is supplied to the valve stem pressing portions 43f and 44f so that the oil supplying amount to the valve stem pressing portions 43f and 44f can be increased.

(73) Further, since the lower face 44d of the exhaust rocker arm 44 is formed on the curved recessed portion 44g which is the lowest portion toward the valve stem pressing portion 44f, oil sticking to the lower face 44d can positively flow to the sliding portion 44e side between the valve stem pressing portion 44f and the exhaust valve stem axial end 19c to collect the oil.

(74) Furthermore, the clearance adjustment members 29 are disposed as separate members between the valve stem pressing portions 43f and 44f of intake and exhaust rocker arms 43 and 44 and the intake and exhaust valve stem axial ends 18c and 19c. Therefore, the necessity for such a screw adjustment mechanism disposed at a tip end of a rocker arm as in a conventional technology is eliminated. Further, since the sliding faces of the valve stem pressing portions 43f and 44f are configured from curved faces, it becomes possible to supply oil flowing along the lower faces 43d and 44d of the intake and exhaust rocker arms 43 and 44 with certainty to the sliding faces of the valve stem pressing portions 43f and 44f, respectively.

(75) Further, the main lubricating oil passage 62 is provided on the connecting bottom wall 73 between the paired support walls 71 and 72 which support the opposite axial ends of the intake and exhaust rocker arm shafts 45 and 46 and is provided in the protuberance 74 which protrudes from the lower face of the connecting bottom wall 73. Consequently, the main lubricating oil passage 62 is provided in the cylinder head 4. Thus, an increase in size of the cylinder head 4 in the heightwise direction can be suppressed.

(76) Furthermore, the sliding portions 43e and 44e are disposed on the upper faces 43c and 44c of the intake and exhaust rocker arms 43 and 44, respectively. Consequently, the injected oil can be supplied to the intake and exhaust valve stem axial ends 18c and 19c without being obstructed by the cam lobes of the intake and exhaust cams 34 and 35 of the intake and exhaust camshafts 32 and 33, respectively.

(77) Where the intake and exhaust rocker arm shafts 45 and 46 are disposed closely to each other, they are disposed in an offset relationship from each other in the cylinder axial line direction and the main lubricating oil passage 62 is disposed in an offset relationship to the intake rocker arm shaft 45 side which is disposed at the higher position. Therefore, the free space can be utilized effectively to dispose the main lubricating oil passage 62 compactly.

(78) The internal combustion engine 1 is mounted on the vehicle such that the tip ends of the intake rocker arm 43 and the exhaust rocker arm 44 are directed obliquely upwardly and obliquely downwardly, respectively. The intake side oil injection oil path 75 to the intake rocker arm 43, disposed at the higher position, is formed such that it is directed toward the tip end of the intake rocker arm 43 while the exhaust side oil injection oil path 76 to the exhaust rocker arm 44 disposed at the lower position is formed such that it is directed to the pivotally supporting base portion 44a of the exhaust rocker arm 44. Therefore, even where it is difficult to direct an oil injection oil path directly to the tip end of the exhaust rocker arm 44 like the exhaust side oil injection oil path 76, it is possible to allow oil to flow and be supplied to the tip end of the exhaust rocker arm 44 from the pivotally supporting base portion 44a of the exhaust rocker arm 44. Consequently, while a reduction in the length of the exhaust side oil injection oil path 76 is achieved, oil supply can be carried out with certainty.

(79) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.