Lubricant supplying system for DOHC type multi-cylinder internal combustion engine
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lubricant supplying system for a DOHC type multi-cylinder internal combustion engine having a plurality of cylinders arranged in series in a cylinder block, a pair of cam shafts parallel to one another and rotatably supported by a cylinder head and a cam holder which is fixed to the cylinder head at opposite sides of the respective cylinders along the cylinder arranging direction, a plurality of cams including low speed cams corresponding to intake and exhaust valves of the respective cylinders and fixed to the cam shafts, a plurality of rocker arms disposed to be slidably contacted with the respective cams and corresponding to each of the intake and exhaust valves of the respective cylinders, and a connection switching mechanism for switching connection and disconnection of the rocker arms in response to a hydraulic pressure to vary operating states of the intake and exhaust valves responsive to an operating state of the engine. 
     2. Description of the Prior Art 
     Conventionally, such internal combustion engine has been known, for example, from Japanese Patent Application Publication Kokai No. 121812/1987. 
     In such an internal combustion engine, the hydraulic pressure of a connection switching mechanism is varied in response to the operating state of the engine, and it is desirable that the influence of the operation of the connection switching mechanism does not influence the supply of lubricant. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a lubricant supplying system for a DOHC type multi-cylinder internal combustion engine which is set free of the above-noted problems, simple in structure and can stably supply lubricant irrespective of the operation of a connection switching mechanism. 
     According to the present invention, the above object is accomplished by providing a lubricant supplying system for a DOHC type multi-cylinder internal combustion engine in which a hydraulic pressure supply passage independent from a lubricant supply passage for supplying a hydraulic pressure to a connection switching mechanism is provided in a cylinder substantially at the center along the arranging direction of cylinders to be vertically extended, and a branch lubricant passage is provided to be branched to the intake and exhaust sides in a cam holder disposed substantially at the center along the arranging direction of the respective cylinders for communicating with the upper end of the hydraulic pressure supply passage to supply lubricant to the slidably contacting portions of low speed cams of the respective cylinders at both intake and exhaust sides with the rocker arms and the cam journal portions of the cam shafts. 
     According to the arrangement described above, the lubricant is supplied to the slidably contacting surfaces of the low speed cams with the rocker arms and the cam journal portions of the cam shafts irrespective of the operation of the connection switching mechanism, and the hydraulic pressure supply passage and the branch lubricant passage are disposed substantially at the center along the arranging direction of the respective cylinders. Therefore, it can prevent a time lag of supplying the lubricant to the portions to be lubricated, and can substantially equalize flowing pressure loss of the lubricant to the portions to be lubricated, thereby uniformly supply the lubricants to the respective portions to be lubricated. Further, only one hydraulic pressure supply passage is provided, the fabrication of the cylinder head becomes simple. 
     According to another aspect of the invention, a low speed hydraulic pressure supply passage is provided substantially at the center along the arranging direction of the respective cylinders in the cylinder head and, a high speed hydraulic pressure supply passage opened at one end face along the arranging direction of the respective cylinders is provided independent from the low speed hydraulic pressure supply passage. Branch lubricant passages for supplying lubricant to slidably contacting portions of the cams, including at least the low speed cams of the respective cylinders at the intake and exhaust sides with the rocker arms, and the branch lubricant passages communicating with the low speed hydraulic pressure supply passage to supply the lubricant to the cam journals of the cam shafts are provided to be branched at the intake and exhaust sides at the cam holder disposed substantially at the center along the arranging direction of the respective cylinders. The connection switching mechanisms and the lubricant supply passage for supplying the lubricant to the sliding contacting portions of the high speed cams with the rocker arms are coaxially provided in both the rocker shafts, a connection passage for communicating through both the lubricant supply passages is provided in the cylinder head near one end along the arranging direction of the respective cylinders, and a lubricant supply port opened at one end face of the cylinder head is provided in communication with one lubricant supply passage. A switching valve for switching the communication and the disconnection between the opening of the high speed hydraulic pressure supply passage and the lubricant supply port is mounted at one end face of the cylinder head. 
     According to the arrangement described above, the lubricant supply to the slidably contacting portions of the cams including at least the low speed cams with the rocker arms and the cam journals, and the lubricant supply to the connection switching mechanism and the slidably contacting portions of the high speed cams with the rocker arms are conducted independently from each other. Therefore, the lubricant is always sufficiently supplied to the slidably contacting portions of the cams including at least the low speed cams with the rocker arms and the cam journals irrespective of the connection switching mechanism supplied with the lubricant in response to the operating state of the engine. Further, since the low speed hydraulic pressure supply passage and the branch lubricant passage are disposed substantially at the center along the arranging direction of the respective cylinders, it can prevent a time lag of supplying the lubricant to the portions to be lubricated, and the flowing pressure loss to the portions to be lubricated can be substantially equalized to equalize the quantities of the lubricants to the respective portions to be lubricated. In addition, the lubricant supplies of the connection switching mechanisms can be switched at between the intake and exhaust sides merely by mounting a single switching valve at one end face of the cylinder head, and, further, since only one low and high speed hydraulic pressure supply passages are provided in the cylinder head, the fabrication of the cylinder head becomes simple. 
     The above and other objects, features and advantages of the invention will become apparent from reading of the following description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 to 12 illustrate one embodiment of the present invention, wherein FIG. 1 is a longitudinal sectional view of the essential portion of an internal combustion engine in section taken along line I--I of FIG. 2, FIG. 2 is a view as seen from arrows with lines II--II of FIG. 1; FIG. 3 is a sectional view taken along line III--III of FIG. 2; FIG. 4 is a sectional view taken along line IV--IV of FIG. 1; FIG. 5 is a sectional view taken along line V--V of FIG. 2; FIG. 6 is a lateral sectional view for showing a connection switching mechanism; FIG. 7 is a view showing a lubricant supplying system; FIG. 8 is a view as seen from arrows with lines VIII--VIII of FIG. 2; FIG. 9 is a sectional view taken along line IX--IX of FIG. 8; FIG. 10 is an enlarged sectional view taken along line X--X of FIG. 8 when a switching valve is closed; FIG. 11 is a sectional view taken along line XI--XI of FIG. 2; and FIG. 12 is a sectional view corresponding to FIG. 10 when the switching valve is opened. 
     FIGS. 13 to 15 illustrate another embodiment of the present invention, wherein FIG. 13 is a view of a lubricant supply system corresponding to FIG. 7; FIG. 14 is a plan view corresponding to FIG. 2; and FIG. 15 is a view as seen from arrows with lines XV--XV of FIG. 14. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described by way of embodiments with reference to the accompanying drawings. 
     Referring first to FIGS. 1 to 12, an embodiment of the present invention will now be described. In FIGS. 1 and 2, in this DOHC type multi-cylinder internal combustion engine, four cylinders 2 are aligned in series in a cylinder block 1, and combustion chambers 5 are defined between a cylinder head 3 coupled to the upper end of the cylinder block 1 and pistons 4 slidably fitted into the respective cylinders 2. At the cylinder head 3 are formed a pair of intake openings 6 and a pair of exhaust openings 7 at the portions forming the ceilings of the respective combustion chambers 5. The intake openings 6 respectively communicate with intake ports 8 opened on one side face of the cylinder head 3, and the exhaust openings 7 respectively communicate with exhaust ports 9 opened on the other side face of the cylinder head 3. 
     Guide cylinders 11i and 11e are respectively fixedly secured to the portions of the cylinder head 3 corresponding to the cylinders 2 to guide a pair of intake valves 10i for opening and closing the respective intake openings 6 and a pair of exhaust valves 10e for opening and closing the respective exhaust openings 7. Valve springs 13i and 13e are respectively provided in resiliently contraction manner between the collars 12i and 12e formed at the upper ends of the intake and exhaust valves 10i and 10e protruded upwards from the guide cylinders 11i and 11e and the cylinder head 3 to thereby urge the intake and exhaust valves 10i and 10e upwards, i.e., in valve closing direction. 
     An operation chamber 15 is formed between the cylinder head 3 and a head cover 14 coupled to the upper end of the cylinder head 3. In the operation chamber 15 are contained and disposed an intake side valve actuating unit 17i for driving to open or close the intake valves 10i in the respective cylinders 2 and an exhaust side valve actuating unit 17e for driving to open or close the exhaust valve 10e in the respective cylinders 2. Both the valve actuating units 17i and 17e fundamentally have the same structure. In the foregoing description, one of the valve actuating units 17i and 17e will be described in detail with suffix &#34;i&#34; or &#34;e&#34; to the reference numerals, and the other will be merely illustrated by adding suffix &#34;i&#34; or &#34;e&#34; to the reference numerals. 
     Referring to both FIGS. 3 and 4, the intake side valve actuating unit 17i includes a cam shaft 18i rotatably driven at a reduction gear ratio of 1/2 from the crankshaft (not shown) of the engine, low speed cams 19i and 20i and high speed cams 21i provided at the cam shaft 18i corresponding to the respective cylinders 2, rocker shafts 22i fixedly disposed in parallel with the cam shaft 18i, first driving rocker arms 23i, second driving rocker arms 24i and free rocker arms 25i pivotally secured to the rocker shaft 22i corresponding to the respective cylinders 2, and hydraulic connection switching mechanisms 26i provided among the rocker arms 23i, 24i, 25i corresponding to the respective cylinders 2. 
     Referring also to FIG. 5, the cam shaft 18i is arranged rotatably around an axis in parallel with the arranging direction of the respective cylinders 2 above the cylinder head 3. Namely, at the cylinder head 3 are provided integrally cam supports 27 and 27 at both ends thereof along the arranging direction of the respective cylinders 2, three cam supports 28, . . . are integrally provided at the corresponding positions between the cylinders 2, and the cam shaft 18i is supported rotatably around the axis by cam holders 29 and 29 fitted onto the cam supports 27 and 27 of both ends, cam holders 30, . . . fitted onto the three cam supports 28, . . . , and the cam supports 27, 27 and 28, . . . . Further, the cam holders 29 are independently provided at the intake and exhaust side valve actuating units 17i and 17e, respectively, while the cam holders 30 are commonly arranged at both the valve actuating units 17i and 17e. On the upper surfaces of the cam supports 27, 27 and 28, . . . are provided semicircular supporting faces 31 for supporting the outer peripheral surfaces of the lower halves of the cam shafts 18i and 18e, and on the lower surfaces of the cam holders 29 and 30 are provided semicircular supporting faces 32 for supporting the outer peripheral surfaces of the upper halves of the cam shafts 18i and 18e. 
     At the respective cam supports 27, 27 and 28, . . . are opened a pair of insertion holes 34 to which bolts 33 are inserted to screw the cylinder head 3 into the cylinder block 1 to be extended upwards and downwards at the positions corresponding to the cam shafts 18i and 18e, and operation holes 35 for rotatably operating the bolts 33 opened at the upper positions corresponding to the insertion holes 34 to be extended upwards and downwards while the upper ends are opened at the semicircular supporting faces 31. 
     At the cylinder head 3 among the cam supports 27, 27 and 28, . . . at the portion corresponding to the center of the respective cylinders 2 is integrally provided a cylindrical central block 36 extending upwards and downwards, and the central block 36 is connected by supporting walls 27 to the cam supports 27, 27 and 28, . . . of both sides. A cylindrical central block 49 connected to the central block 36 is provided at the head cover 1. In the central blocks 36 and 49 are opened plug insertion holes 38, into which an ignition plug 39 fitted into the combustion chamber 5 is fitted. 
     At one ends projected from the cylinder head 3 and the head cover 14 of both the cam shafts 18i and 18e are fixedly secured timing pulleys 40 and 41, and a timing belt 42 for transmitting a driving force from a crankshaft (not shown) is suspended between both the timing pulleys 40 and 41. In this manner, both the cam shafts 18i and 18e are rotated in the same direction. 
     The low speed cams 19i and 20i are integrated at the positions corresponding to the intake valves 10i with the cam shaft 18i, and the high speed cam 21i is integrated between both the low speed cams 19i and 20i. On the other hand, the rocker shaft 22i is fixedly held by the cam supports 27, 27 and 28, . . . at an axis parallel to the cam shaft 18i at a position lower than the cam shaft 18i. At the rocker shaft 22i are pivotally secured adjacently to each other the first driving rocker arm 23i operatively connected to one intake valve 10i, the second driving rocker arm 24i operatively connected to the other intake valve 10i, and the free rocker arm 25i disposed between the first and second driving rocker arms 28i and 24i. 
     Tappet screws 43i are respectively screwed into the first and second driving rocker arms 23i and 24i for advancing and retreating movements to be contacted with the upper ends of the intake valves 10i corresponding to the tappet screws 43i, thereby operatively connecting both the driving rocker arms 23i and 24i to the intake valves 10i. 
     The free rocker arm 25i is resiliently urged in a direction for slidably contacting with the high speed cam 21i by a lost motion mechanism 44i interposed to the cylinder head 3. The lost motion mechanism 44i includes a bottomed cylindrical guide member 45 fitted to the cylinder head 3 with the closed end disposed at the cylinder head 3 side, a piston 36 slidably fitted into the guide member 45 and contacted with the lower surface of the free rocker arm 25i, and first and second springs 47 and 48 interposed in series between the piston 46 and the guide member 45 to urge the piston 46 to the side of the free rocker arm 25i. The first and second springs 47 and 48 are set with different spring constants from one another. 
     In FIG. 6, the connection switching mechanism 26i includes a first switching pin 51 for connecting between the first rocker arm 23i and the free rocker arm 25i, a second switching pin 52 for connecting between the free rocker arm 25i and the second driving rocker arm 24i, a restriction pin 53 for restricting the movement of the first and second switching pins 51 and 52, and a return spring 54 for urging the pins 51 to 53 to the side of releasing the connection. 
     At the first driving rocker arm 23i is opened in parallel with the rocker shaft 22i a first bottomed guide hole 55 opened at the side of the free rocker arm 25i, the first switching pin 51 is slidably fitted into the first guide hole 55, and a hydraulic pressure chamber 56 is defined between the one end of the first switching pin 51 and the closed end of the first guide hole 55. Further, at the first driving rocker arm 23i is opened a passage 57 communicating with the hydraulic pressure chamber 56, a lubricant supply passage 58i is provided in the rocker shaft 22i, and the lubricant supply passage 58i always communicates with the hydraulic pressure chamber 56 through a passage 57 irrespective of the rocking state of the first driving rocker arm 23i. 
     At the free rocker arm 25i is opened a guide hole 59 corresponding to the first guide hole 55 over both sides in parallel with the rocker shaft 22i, and the second switching pin 52 contacted at one end with the other end of the first switching pin 51 is slidably fitted into the guide hole 59. 
     At the second driving rocker arm 24i is opened a second bottomed guide hole 60 corresponding to the guide hole 59 at the side of the free rocker arm 25i in parallel with the rocker shaft 22i, and the disc-like restriction pin 53 contacted with the other end of the second switching pin 52 is slidably fitted into the second guide hole 60. Further, a guide cylinder 61 is fitted to the closed end of the second guide hole 60, and a shaft 62 slidably fitted into the guide cylinder 61 is coaxially and integrally projected at the restriction pin 52. The return spring 54 is disposed between the guide cylinder 61 and the restriction pin 53, and the pins 51, 52, 53 are urged by the return spring 54 to the side of the hydraulic pressure chamber 56. 
     In such a connection switching mechanism 26i, when the hydraulic pressure of the hydraulic pressure chamber 56 is raised, the first switching pin 51 is fitted into the guide hole 59, and the second switching pin 52 is fitted into the second guide hole 60 to connect the rocker arms 23i, 25i and 24i. When the hydraulic pressure of the hydraulic pressure chamber 56 is, on the other hand, lowered, the first switching pin 51 is returned by the resilient force of the return spring 54 at the contacting surface with the second switching pin 52 to a position corresponding to between the first driving rocker arm 23i and the free rocker arm 25i, and the second switching pin 52 is returned at the contacting surface with the restriction pin 53 to a position corresponding to between the free rocker arm 25i and the second driving rocker arm 24i. Thus, the connecting state of the rocker arms 23i, 25i and 24i is disconnected. 
     Then, referring to FIG. 7, a lubricant supplying system to both the valve actuating units 17i and 17e will be described. To the exhaust port of an oil pump 64 for pumping lubricant from an oil pan 63 are connected an oil gallery 68 through a relief valve 65, an oil filter 66 and an oil cooler 67, the hydraulic pressure is supplied from the oil gallery 68 to the respective connection switching mechanisms 26i, 26e, and lubricant is supplied to the portions to be lubricated of the valve actuating units 17i and 17e. 
     To the gallery 68 are connected lubricant supply passages 58i and 58e in the rocker shafts 22i and 22e through a switching valve 69 for switching the hydraulic pressure passed through a filter 70 provided on the way thereto to high or low pressure to supply it. Further, the lubricant supply passages 58i and 58e are so formed in a tapered shape as to increase in diameter the one end thereof at the side of the switching valve 69 and to decrease in diameter the other end thereof. 
     On the upper surfaces of the cam holders 29, 29 and 30, . . . are screwed passage forming members 72i and 72e extended in parallel corresponding to both the cam shafts 18i and 18e by a plurality of bolts 73. Further, at the passage forming members 72i and 72e are provided in parallel low speed lubricant passages 74i and 74e closed at both ends, and high speed lubricant passages 75i and 75e communicating with the lubricant supply passages 58i and 58e through throttles 76i and 76e. 
     As shown in FIGS. 5 and 7, a lubricant passage 77 having a throttle 79 on the way to be branched from the oil gallery 68 at the upstream side from the filter 70 is provided to be extended upwards in the cylinder block 1. Further, the passage 77 is provided in the cylinder block 1 substantially at the center along the arranging direction of the respective cylinders 2. On the other hand, a low speed hydraulic pressure supply passage 78 communicating with the passage 77 is provided in the cam support 28 substantially at the center along the arranging direction of the respective cylinders 2, and the supply passage 78 includes an annular passage portion 78a for surrounding the bolt 33, a passage portion 78b extended to the center between both the valve actuating units 17i and 17e in communication with the upper end of the passage portion 78a, and a passage portion 78c extended upward in communication with the passage portion 78b and opened at the upper surface of the cam support 28. 
     At the cam holder 30 disposed substantially at the center along the arranging direction of the respective cylinders 2 is provided a substantially Y-shaped branch lubricant passage 80 branched to both the valve actuating units 17i and 17e in communication at the upper end with the lower end of the passage portion 78c in the low speed hydraulic pressure supply passage 78, and the upper end of the branch lubricant passage 80 communicates at the upper end with the low speed lubricant passages 74i and 74e. That is, communication holes 81i and 81e are opened at the passage forming members 72i and 72e, respectively in communication of the branch lubrication passage 80 with the low speed lubricant passages 74i and 74e. 
     The low speed lubricant passages 74i and 74e supply lubricant to the slidably contacting portions of the cams 19i, 19e; 20i, 20e; 21i, 21e with the rocker arms 23i, 23e; 24i, 24e; 25i, 25e, and the cam journals 18i&#39; and 18e&#39; of the cam shafts 18i and 18e. Thus, on the lower surface of the passage forming members 72i and 72e are opened lubricant discharging holes 82i and 82e communicating with the low speed lubricant passages 74i and 74e at positions corresponding to the low speed cams 19i, 19e; 20i, 20e and high speed cams 21i and 21e, and lubricant supply passages 83i and 83e communicating with the low speed lubricant passages 74i and 74e to supply the lubricant to the cam journals 18i&#39; and 18e&#39; of the cam shafts 18i and 18e. 
     The high speed lubricant passages 75i and 75e supply the lubricant to the slidably contacting portions of the high speed cams 21i and 21e with the free rocker arms 25i and 25e, and on the lower surfaces of the passage forming members 72i and 72e are opened lubricant discharging holes 84i and 84e communicating with the high speed lubricant passages 75i and 75e at positions corresponding to the high speed cams 21i and 21e. 
     The passage forming members 72i and 72e are disposed above the cam shafts 18i and 18e, and the lubricants discharged from the lubricant discharging holes 84i and 84e are scattered partly to the sides in response to the rotations of the cam shafts 18i and 18e. Further, since both the cam shafts 18i and 18e are rotated in the same direction, the lubricant discharged from one lubricant discharging hole 84i is partly scattered to the side of the exhaust side valve actuating unit 17e, while the lubricant discharged from the other lubricant discharging hole 84e is scattered partly toward the opposite side to the intake side valve actuating unit 17i. In addition, since the central blocks 36, 49 are provided between both the valve actuating units 17i and 17e of the portions corresponding to the lubricant discharging holes 84i and 84e, the scattered lubricant is partly reflected on the central blocks 36, 49 and returned to a side of the slidably contacting portion of the high speed cam 21i with the free rocker arm 25i. The lubricant scattered from the lubricant discharging hole 84e is partly contacted with the side of the cylinder head 3, reflected and returned to a side of the slidably contacting portion of the high speed cam 21e with the free rocker arm 25e. However, the distances between the slidably contacting portion of the high speed cam 21i with the free rocker arm 25i and the central blocks 36, 49 are shorter than that between the slidably contacting portions of the high speed cam 21e with the free rocker arm 25e and the side of the cylinder head 3, and the lubricant amount reflected from the central blocks 36, 49 and returned to the slidably contacting portion of the high speed cam 21i with the free rocker arm 25i is more than that reflected from the side of the cylinder head 3 and returned to the slidably contacting portion of the high speed cam 21e with the free rocker arm 25e. Therefore, the diameter of the lubricant discharging hole 84i is set to be smaller than that of the lubricant discharging hole 84e, and the lubricant discharging amount from the lubricant discharging hole 84i is set accordingly less than that of the lubricant discharging hole 84e. Further, the throttle degree of the throttle 76i provided between the lubricant supply passage 58i and the high speed lubricant passage 75i is set smaller than that of the throttle 76e provided between the lubricant supply passage 58e and the high speed lubricant passage 75e, and the lubricant amount supplied to the high speed lubricant passage 75i is accordingly set smaller than that supplied to the high speed lubricant passage 75e. 
     Since the lubricant discharging holes 82i and 82e communicating with the low speed lubricant passages 74i and 74e have substantially equal distances between the members for reflecting the lubricant in a direction for scattering the lubricant by the rotations of the cam shafts 18i and 18e and the slidably contacting portions of the low speed cams 19i, 19e; 20i, 20e with the first and second driving rocker arms 23i, 23e; 24i, 24e, the bore diameters of the holes 82i and 82e are set substantially the same. 
     In FIGS. 8 and 9, a lubricant passage 85 extended upwards and downwards near one end along the arranging direction of the respective cylinders 2 is provided independently from the passage 77 in the cylinder block 1, and communicates through the filter 70 (FIG. 7) with the lubricant gallery 68. On the other hand, a high speed hydraulic pressure supply passage 86 communicating with the lubricant passage 85 is provided in the cylinder head 3 at one end thereof along the arranging direction of the cylinders 2, and the supply passage 86 includes a passage portion 86a extended upwards slightly in communication with the upper end of the passage 85, a passage portion 86b further extended to the one end side of the cylinder head 3 in communication with the upper end of the passage portion 86a, a passage portion 86c extended upwards in communication with the passage portion 86b, a passage portion 86d extended to the rocker shaft 22e side of the exhaust valve side valve actuating unit 17e in communication with the upper end of the passage portion 86c, and a passage portion 86e opened at one end face of the cylinder head 3 in communication with the passage portion 86d. 
     Referring also to FIG. 10, at one of the rocker shafts 22i and 22e, i.e., the portion for supporting one end of the exhaust side rocker shaft 22e is opened a lubricant supply port 87 in communication with the lubricant supply passage portion 58e in the rocker shaft 22e to open at one end face of the cylinder head 3. At the cylinder head 3 is opened a communication passage 88 for communicating at the lubricant supply port 87 with the lubricant supply passage 58i in the intake side rocker shaft 22i. 
     The switching valve 69 is mounted on one end face of the cylinder head 3 to switch the connection and the disconnection between the opening to one end face of the cylinder head 3, i.e., the passage portion 86e and the lubricant supply port 87, and includes a spool valve body 92 slidably fitted into a housing 91 having an inlet port 89 communicating with the passage portion 86e and an outlet port 90 communicating with the lubricant supply port 87 and mounted on one end face of the cylinder head 3. 
     In the housing 91 is opened a cylinder bore 94 closed at its upper end with a cap 93 at an axis extending vertically, and the spool valve body 92 is slidably fitted into the cylinder bore 94 by forming an operation hydraulic pressure chamber 93 between the spool valve body and the cap 93. When the cylinder bore 94 is formed at its axis in a vertical direction in this manner, the weight of the spool valve body 92 is not applied to the sliding surface with the bore 94, thereby smoothly operating the spool valve body 92. 
     In a spring chamber 96 formed between the lower portion of the housing 91 and the spool valve body 92 is contained a spring 97 for urging the spool valve body 92 upwards, i.e., in a closing direction. On the spool valve body 92 is formed an annular recess 98 communicating between the inlet port 89 and the outlet port 90. As shown in FIG. 10, when the spool valve body 92 moves upwards, the spool valve body 92 is in a state to cut off the communication between the inlet port 89 and the outlet port 90. 
     An oil filter 99 is interposed between the inlet port 89 and the high speed hydraulic pressure supply passage 88e in the state that the housing 91 is mounted on the end face of the cylinder head 3. In the housing 91 is opened an orifice hole 101 communicating between the inlet port 89 and the outlet port 90. Accordingly, between the inlet port 89 and the outlet port 90 is communicated through the orifice hole 101 even in the state that the spool valve body 92 is closed, and the hydraulic pressure throttled by the orifice hole 101 is supplied from the outlet port 90 to the lubricant supply port 87. 
     In the housing 91 is also opened a bypass port 102 communicating with the outlet port 90 through an annular recess 98 only when the spool valve body 92 is disposed at its closed position, and the bypass port 102 communicates with the upper portion in the cylinder head 3. Further, at the spool valve body 92 is opened an orifice hole 103 communicating at the inlet port 89 with the spring chamber 96 irrespective of the position of the spool valve body 92. Further, in the lower portion of the housing 91 is opened a through hole 104 communicating at the spring chamber 96 with the cylinder head 3, and the lubricant fed through the orifice hole 103 into the spring chamber 96 is returned from the through hole 104 into the cylinder head 3. Thus, since dusts adhered to the spring 97 are fed out by the lubricant, the dusts are avoided to affect the adverse influence to the extending and contracting operations of the spring 97. 
     A conduit 105 always communicating with the inlet port 89 is connected to the housing 91, and the conduit 105 is connected through a solenoid valve 106 to a conduit 107. Further, the conduit 107 is connected to a connection hole 108 opened at the cap 93. Therefore, when the solenoid valve 106 is opened, the hydraulic pressure is supplied into the operation hydraulic pressure chamber 95, and the spool valve body 92 is driven in a valve opening direction by the hydraulic force of the hydraulic pressure introduced into the operation hydraulic pressure chamber 95. 
     In the housing 91 is opened a leakage jet 109 communicating with the intermediate portion of the conduit 107, and the leakage jet 109 communicates with the upper portion in the cylinder head 3. This leakage jet 109 operates to escape the hydraulic pressure remaining in the conduit 107 when the solenoid valve 106 is closed. 
     Further, in the housing 91 is mounted a pressure detector 110 for detecting the hydraulic pressures of the outlet port 90, i.e., the lubricant supply passages 58i and 58e, and the pressure detector 110 operates to detect whether the switching valve 69 is normally operated or not. 
     In FIG. 11, at the ends of the passage forming members 72i and 72e at the other end side of the cylinder head 3, i.e., at the opposite side to the mounting position of the switching valve 69 are opened communication holes 111i and 111e communicating with the high speed lubricant passages 75i and 75e, and on the upper surface of the cam holder 29 are formed a pair of grooves to form passages 112i and 112e communicating with the holes 111i and 111e between the passage forming members 72i and 72e. On the ends of the rocker shafts 22i and 22e are opened communication holes 113i and 113e communicating with the lubricant supply passages 58i and 58e, and the passages 114i and 114e opened at the cylinder head 3 in communication with the holes 113i and 113e communicate through the throttles 76i and 76e opened at the cam holder 29 with the passages 112i and 112e, respectively. Accordingly, the lubricant supplied to the lubricant supply passages 58i and 58e are supplied through the throttles 76i and 76e to the high speed lubricant passages 75i and 75e. 
     The operation of the embodiment described above will now be described. Since the lubricant is supplied through the lubricant passage 77 independent from the connection switching mechanisms 26i and 26e, low speed hydraulic pressure supply passage 78 and the branch lubricant passage 80 to the low speed lubricant passages 74i and 74e, even if the hydraulic pressure is controlled by the switching valve 69 to operate the connection switching mechanisms 26i and 26e, the predetermined hydraulic pressure can be always supplied irrespective of the operations, and the lubricant can be supplied under stable pressure to the slidably contacting portions of the low speed cams 19i, 19e; 20i, 20e with the rocker arms 23i, 23e; 24i, 24e, the slidably contacting portions of the high speed cams 21i, 21e with the free rocker arms 25i, 25e, and the cam journals 18i&#39; and 18e&#39; of the cam shafts 18i and 18e. 
     Further, since the lubricant passage 77, the low speed hydraulic pressure supply passage 78 and the branch lubricant passage 80 are arranged substantially at the center along the arranging direction of the respective cylinders 2, the flowing pressure losses of the lubricant to the lubricant discharging holes 82i and 82e, and the lubricant supply passages 83i and 83e can be maintained substantially constant to substantially uniformize the lubricant amount. 
     When the connection switching mechanisms 26i and 26e are switched to set the intake and exhaust valves 10i and 10e to high speed operation state, the switching valve 69 is opened as shown in FIG. 12. Namely, the solenoid valve 106 is opened to supply the hydraulic pressure to the operation hydraulic pressure chamber 95 to open the spool valve body 92, thereby supplying the hydraulic pressure to the lubricant supply passages 58i and 58e. Thus, the hydraulic pressure is supplied to the hydraulic pressure chamber 56 to connect to operate the connection switching mechanism 26, thereby opening or closing the exhaust valve 10e in high speed operation state. 
     Further, since the lubricant supply passages 58i and 58e are formed in the tapered shape with large diameter at the side of the switching valve 69 when the hydraulic pressure to the passages 58i and 58e is switched in this manner, the flowing sectional area is reduced as the number of the connection switching mechanisms 26i and 26e for supplying the hydraulic pressure is decreased, thereby substantially maintaining the flowing velocity of the hydraulic pressure along the axial direction of the lubricant supply passages 58i and 58e. Accordingly, the displacement of the hydraulic pressure operating timing to the hydraulic pressure connection switching mechanisms 26i and 26e arranged at an axial interval of the supply passages 58i and 58e is avoided as much as possible, and the operation altering timing of the intake and exhaust valves 10i and 10e in the respective cylinders 2 can be brought substantially into coincidence. 
     The lubricant supplied to the high speed lubricant passages 75i, 75e is discharged from the lubricant discharging holes 84i and 84e in the above-described high speed operation state, and the lubrication of the slidably contacting portions of the high speed cams 21i and 21e with the free rocker arms 25i and 25e in which the surface pressures are particularly increased can be sufficiently conducted. Further, since the the diameters of the lubricant discharging holes 84i and 84e are set in response to the distance between the member for reflecting the lubricant scattered in response to the rotations of the cam shafts 18i and 18e and the slidably contacting portions of the high speed cams 21i and 21e with the free rocker arms 25i and 25e and the throttling degrees of the throttles 76i and 76e are set, the lubricant amounts supplied to the slidably contacting portions can be substantially uniformized. 
     When the switching valves 69i and 69e are switched to switch the low speed operation state to the high speed operation state, there is a slight time lag until the hydraulic pressures of the high speed lubricant passages 75i and 75e are increased due the throttles 76i and 76e, and there is a slight time delay until the lubricant is discharged from the lubricant discharging holes 84i and 84e. However, since the lubricant discharging holes 82i and 82e communicating with the low speed lubricant passages 74i and 74e are also arranged at the positions corresponding to the slidably contacting portions of the high speed cams 21i and 21e with the free rocker arms 25i and 25e, even if there is the slight time delay as described above, the lubricant is not insufficient at the slidably contacting portions of the high speed cams 21i and 21e with the free rocker arms 25i and 25e. When the switching valve 69 is closed to generate the low speed operation state while the pins 51, 52, 53 remain locked at the connection switching mechanisms 26i and 26e, the surface pressures of the slidably contacting portions of the high speed cams 21i and 21e with the free rocker arms 25i and 25e become high the same as that at the time of high speed operation state. However, at this time, the lubricant is discharged from the lubricant discharging hole 82i and 82e communicating with the low speed lubricant passages 74i and 74e to the slidably contacting portions of the high speed cams 21i and 21d with the free rocker arms 25i and 25e, and the sufficient lubricant can be accordingly supplied thereto. 
     When the opening and closing operation states of the intake and exhaust valves 10i and 10e are switched from high speed operation state to the low speed operation state, the solenoid valve 106 is closed. When the solenoid valve 106 is closed, the hydraulic pressure in the conduit 107 is escaped from the leakage jet 109 to rapidly release the hydraulic pressure of the operation hydraulic pressure chamber 95, and the switching valve 69 is rapidly closed in response to the release of the hydraulic pressure. Further, when the switching valve 69 is closed, the hydraulic pressures in the lubricant supply passages 58iand 58e are escaped through the bypass port 102 into the cylinder head 3. Accordingly, the hydraulic pressure in the hydraulic pressure chamber 56 in the lubricant supply passages 58i and 58e, i.e, the connection switching mechanism 26i and 26e is rapidly reduced, thereby improving the switching responsiveness of the high speed operation state to the low speed operation state. 
     In such a lubricant supplying system, the low and high speed hydraulic pressure supply passages 78 and 86 may be provided each one in the cylinder head 3. Therefore, the fabrication of the cylinder head 3 can be very facilitated. Further, since the switching valve 69 is mounted on one end face of the cylinder head 3, its mounting structure becomes simple. Moreover, since the lubricant supply passages 58i and 58e are commonly used to supply the lubricant to the connection switching mechanisms 26i and 26e and to the high speed lubricant passages 75i and 75e, it is unnecessary to provide separately the lubricant supply conduits and the lubricant supply passages in the cylinder head 3, thereby efficiently supplying the lubricant while avoiding the increases in the number of components and the number of manufacturing steps. 
     FIGS. 13 to 15 show another embodiment of the present invention, wherein corresponding parts will be indicated by corresponding numerals and characters in the embodiments. 
     Switching valves 69i and 69e are connected in parallel for switching hydraulic pressure passed through a filter 70 provided on the way in an oil gallery 68 communicating with an oil pump 64 to high or low pressure to be supplied, and lubricant supply passages 58i and 58e in rocker shafts 22i and 22e are connected through corresponding switching valves 69i and 69e to the oil gallery 68. Further, pressure detectors 110i and 110e are provided in the switching valves 69i and 69e, respectively. 
     In a cylinder head 3 are opened hydraulic pressure supply passages 88i and 88e opened to one end face of the cylinder head 3 in communication with the passages portion 86d of a high speed hydraulic pressure supply passage 86. Further, at the portions of the cylinder head 3 for supporting the one ends of both the rocker shafts 22i and 22e are lubricant supply passages 87i and 87e communicating with the lubricant supply passages 58i and 58e in the rocker shafts 22i and 22e to be opened to one end face of the cylinder head 3. 
     The switching valves 69i and 69e are mounted at one end face of the cylinder head 3 to switch the connection and the disconnection between the hydraulic pressure supply passages 88i and 88e and the lubricant supply passages 87i and 87e, and the valves 69i and 69e are arranged fundamentally identical with the switching valve 69 of the previous embodiment while the housing 91 is common. 
     According to the embodiments described above, the switching valves 69i and 69e are individually controlled in their operations to independently control the supply and the stop of the lubricant to the lubricant supply passages 58i and 58e of the intake and exhaust sides to control the movements of the valves by differentiating the operation states of the intake and exhaust valves 10i and 10e, thereby increasing the degree of freedoms of controlling the moving valves.