Patent Publication Number: US-7717081-B2

Title: Engine cylinder head structure

Description:
FIELD OF THE INVENTION 
   This invention relates to a structure of a cylinder head of an engine, and more particularly to a structure of the cylinder head of an engine with a variable valve timing mechanism. 
   BACKGROUND OF THE INVENTION 
   An engine with a hydraulically-driven variable valve timing mechanism includes an actuator disposed at an end of a camshaft, an actuator oil passage as an operating oil path for introducing oil from an oil pump to the actuator, and a camshaft oil passage as a lubricating oil path for introducing the oil to the camshaft. 
   Conventionally, an engine comprises structures forming an oil passage for the engine, which include an operating oil path in communication to an end journal at an end of a camshaft in a cylinder head to introduce the oil to an actuator for a variable valve timing mechanism, and a camshaft lubricating oil path in communication to a camshaft housing of a journal adjacent to the end journal. 
   Also there are some structures of an oil passage for the engine, which include an operating oil path in communication to a camshaft housing journal section of the end journal of the camshaft to introduce the oil to the actuator for the variable valve timing mechanism, and a lubricating oil path also in communication to the end journal of the camshaft. 
   Prior Art 
   The following documents 1 and 2 form the prior art of which the present applicant has presently knowledge 
   Document 1: JP No. 2000-110536A 
   Document 2: JP No. 2000-199417A 
   DISCLOSURE OF THE INVENTION 
   Problems to be Solved by the Invention 
   Conventionally, in the structure of the oil passage as disclosed in JP No. 2000-110536A, an oil pipe is disposed in the lubricating oil path of the camshaft. It therefore increases the number of components and also requires arrangement of oil pipes so as not to interfere with the camshaft and a cylinder head cover, resulting in constraint of layout. 
   Also according to JP No. 2000-199417A, the end journal of the camshaft is increased in length to disadvantageously lengthen the engine. Where the end journal is made shorter in length, the operating oil pressure for the variable valve timing mechanism cannot be fully obtained. 
   To obviate above-mentioned inconveniences in a cylinder head of an engine equipped with a variable valve timing mechanism, the present invention provides a simplified structure of an oil passage including an actuator oil passage for introducing the oil to an actuator for the variable valve timing mechanism and a camshaft bearing oil passage for lubricating a camshaft bearing section of a camshaft, while fully obtaining the operating oil pressure for the variable valve timing mechanism. This reduces the number of components and allows the cylinder head to be made smaller in size to downsize the engine, which promotes productivity. A boss section having the oil passage therein provides proper flow of cooling water in the cylinder head. 
   Means to Solve the Problems 
   The present invention provides a structure of a cylinder head of an engine, having more than one camshaft bearing section formed on top of the cylinder head and arranged in an axial direction of a camshaft, the camshaft bearing section rotatably supporting the camshaft; an actuator of a variable valve timing mechanism attached to the camshaft at a protruding section from an edge wall of the cylinder head; an oil control valve disposed in a chain case that covers the edge wall of the cylinder head; a cylinder head-side oil passage formed in the edge wall of the cylinder head by which oil is supplied from the cylinder block side, the cylinder head-side oil passage having a downstream end branched into an actuator oil passage in communication to the actuator through the oil control valve and a camshaft bearing oil passage in communication to the camshaft bearing section; a valve upstream-side passage section formed in the edge wall of the cylinder head as the actuator oil passage for communicating between the cylinder head-side oil passage and the oil control valve; a valve downstream-side passage section for communicating between the oil control valve and a first camshaft bearing section above the edge wall of the cylinder head; a communication passage section as the camshaft bearing oil passage for communicating the cylinder head-side oil passage with a second camshaft bearing section adjacent to the first camshaft bearing section in the axial direction of the camshaft, comprising the improvement wherein a partition wall is disposed in the cylinder head to separate an upward valve operating chamber from a downward water jacket; a boss section is formed at a position lower than the partition wall in the edge wall of the cylinder head, and has one end joined to the chain case and the other end protruding into the water jacket; a branch oil passage is formed in the boss section and extends linearly into the water jacket from a joint surface with the chain case, and has a middle section to which the cylinder head-side oil passage is connected, the branch oil passage having the valve upstream-side passage section specified by a section toward the chain case with respect to a junction Keith the cylinder head-side oil passage; and the linear communication passage section communicates between an end portion of the branch oil passage protruding into the water jacket and a camshaft cap coupling surface of the second camshaft bearing section. 
   Effects of the Invention 
   According to the structure of the cylinder head of the engine of the present invention, the oil passage structure including the actuator oil passage and the camshaft bearing oil passage can be simplified while fully maintaining the operating oil pressure to the variable valve timing mechanism, reducing the number of components and providing a smaller cylinder head to downsize the engine promoting productivity. The boss section having the oil passage therein provides proper flow of cooling water in the cylinder head. 
   BEST MODE FOR CARRYING OUT THE INVENTION 
   In order to downside the engine and to promote productivity, the present invention provides the simplified structure of the oil passage including the actuator oil passage for conducting the oil to the actuator of the variable valve timing mechanism and the camshaft bearing oil passage for lubricating the camshaft bearing section. In order to provide proper flow of the cooling water in the cylinder head, the present invention provides the boss section having the oil passage therein. 
   Embodiments of the present inventions are explained in detail with reference to drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a cylinder head taken along line  1 - 1  of  FIG. 2 . 
       FIG. 2  is a right side view of a cylinder head according to a first embodiment of the present invention. 
       FIG. 3  is a perspective view of a cylinder head according to a first embodiment of the present invention. 
       FIG. 4  is a plan view of a cylinder head according to a first embodiment of the present invention. 
       FIG. 5  is a cross-sectional view of a cylinder head according to a first embodiment of the present invention. 
       FIG. 6  is a right side view of an engine from which a chain case is detached according to a first embodiment of the present invention. 
       FIG. 7  is a right side view of an engine according to a first embodiment of the present invention. 
       FIG. 8  is a perspective view of a cylinder head according to a second embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF A FIRST EMBODIMENT OF THE INVENTION 
     FIGS. 1-5  illustrate a first embodiment of the present invention.  FIGS. 6 and 7  show a multi-cylinder engine  1  for mounting on a vehicle. 
   The engine  1  is installed transversely of the vehicle and includes a cylinder block  2 , a cylinder head  3 , a cylinder head cover  4 , and an oil pan  5 . To the engine  1 , a chain case  7  is attached which defines a chain chamber  6  over a right side of the cylinder block  2  and the cylinder head  3 . As shown in  FIG. 1 , the chain case  7  is joined to a joining surface  8 A of an edge wall  8  of the cylinder head  3 . 
   Referring to  FIG. 1 , the cylinder head  3  has combustion chambers  9 , corresponding to respective cylinders, formed in a lower section thereof. The cylinder head  3  also has in an upper section an ignition plug hole wall  11  defining an ignition plug hole  10 , and a valve operating chamber  12  on the periphery of the ignition plug hole wall  11 . 
   As shows in  FIG. 5 , the cylinder head  3  includes an intake port  13  for respective cylinders formed on an intake side, a rear side, for conducing the intake air to the combustion chambers  9 , and an exhaust port  14  for respective cylinders formed on an exhaust side, a front side, for conducting the exhaust gas from the combustion chambers  9 . 
   Further referring to  FIG. 1 , the cylinder head  3  includes a water jacket  15  around the intake port  13 , and a cooling water introducing passage  16  for conducting the cooling water to the water jacket  15 . The cooling water introducing passage  16  comprises an intake-side cooling water introducing passage  16 A and an exhaust-side cooling water introducing passage  16 B. 
   As shown in  FIG. 7 , the chain case  7  includes, in an upper part toward the cylinder head  3 , a protuberance section  17  formed rearwardly on the intake side, and a depressed section  18  and an engine mount attaching section  19  which are formed forwardly on the exhaust side. 
   As shown in  FIGS. 6 and 7 , in an upper side of the cylinder block  2  and in the rearward intake side, a water pump  22  equipped with a water pump pulley  21  is mounted through a water pump mounting section  20 . The water pump mounting section  20  includes a pump mounting surface  23 , a pump inlet  24 , and pump outlet  25 . The water pump  22  supplies the cooling water to the cooling water introducing passage  16  in the cylinder head  3 . 
   In the cylinder block  2 , an alternator  29  with an alternator pulley  28  is attached rearwardly of the water pump  22 , which is supported by an upper alternator arm  26  and a lower alternator arm  27 . 
   As shown in  FIGS. 6 and 7 , a crankshaft  30  is supported in the cylinder block  2 . The crankshaft  30  includes on a right side a crank pulley  31 , a trochoid oil pump  32 , and a timing sprocket  33 . The oil pump  32  is formed by an oil pump plate  34  in a lower part of the chain case  7  and is driven by rotation of the crankshaft  30  to generate the oil pressure. 
   Also as shown in  FIG. 6 , the cylinder block  2  includes a main gallery  35  formed in an axial direction X of a camshaft (transversely of the vehicle) for introducing the oil from the oil pump  32 . The cylinder block  2  also includes a cylinder block-side oil passage  36  extending upwardly and branched from the main gallery  35 . 
   Further as shown in  FIG. 6 , at the bottom of the cylinder block  2 , an intake pipe  38  equipped with an oil strainer  37  is attached so as to be connected to the oil pump  32 . 
   As shown in  FIG. 7 , a belt  39  passes around the water pump pulley  21 , the alternator pulley  28 , and the crank pulley  31 . 
   Referring to  FIG. 4 , in the upper part of the cylinder head  3 , a plurality of camshaft bearing sections  40 , i.e. a first camshaft bearing section  40 A, a second camshaft bearing section  40 B, etc., are arranged in the axial direction X of the camshaft (transverse direction of the vehicle). 
   Lower portions of the camshafts, an intake camshaft  41  and an exhaust camshaft  42  are rotatably supported by the first camshaft bearing section  40 A, the second camshaft bearing section  40 B, etc. 
   As shown in  FIG. 1 , upper portions of the intake camshaft  41  and the exhaust camshaft  42  are rotatably supported by a plurality of camshaft housings  43 , i.e. a first camshaft housing  43 A, a second camshaft housing  43 B, etc. 
   As shown in  FIG. 6 , the intake camshaft  41  has a right end to which an intake camshaft sprocket  44  is attached; the exhaust camshaft  42  has a right end to which an exhaust camshaft sprocket  45  is attached. 
   In the chain chamber  6 , a timing chain  46  passes around the timing sprocket  33 , the intake camshaft sprocket  44 , and the exhaust camshaft sprocket  45 . 
   Referring to  FIGS. 3 and 4 , an actuator  48  of a variable valve timing mechanism  47  is attached to the intake camshaft  41  at a portion protruding from the edge wall  8  of the cylinder head  3 . 
   As shown in  FIGS. 2 ,  6 , and  7 , an oil control valve  49  of the variable valve timing mechanism  47  is attached to the chain case  7  that covers the edge wall  8  of the cylinder head  3 . The oil control valve  49  integrates a solenoid section  50  and a spool portion  51 ; the spool portion  51  is inserted inner of the chain case  7  from a stepped portion of the depressed section  18  outside the chain case  7 , while the solenoid section  50  is positioned in the depressed section  18 . 
   As shown in  FIGS. 1 and 6 , in the edge wall  8  of the cylinder head  3 , a cylinder head-side oil passage  52  is formed by which the oil is supplied from the cylinder block  2  side. 
   A downstream end of the cylinder head-side oil passage  52  is branched into an actuator oil passage (operating oil path)  53  in communication to the actuator  48  through the oil control valve  49  and a camshaft bearing oil passage (lubrication oil path)  54  in communication to the second camshaft bearing section  40 B. 
   An upstream end of the cylinder-head side oil passage  52  is communicated to the cylinder-block side oil passage  36  of the cylinder block  2 . 
   As shown in  FIG. 1 , in the edge wall  8  of the cylinder head  3 , the actuator oil passage  53  includes a valve upstream-side passage section  55 A communicating between the cylinder head-side oil passage  52  and the oil control valve  49 , and a valve downstream-side passage section  55 B communicating between the oil control valve  49  and the first camshaft bearing section  40 A that is positioned above the edge wall  8  of the cylinder head  3 . 
   As shown in  FIGS. 2 ,  3 , and  6 , the valve downstream-side passage section  55 B includes a valve timing retard passage  56  and a valve timing advance passage  57 , which extend upwardly for introducing the oil from the oil control valve  49  to the actuator  48  side. 
   Also as shown in  FIG. 2 , a camshaft housing retard passage  58  in communication to the valve timing retard passage  56 , and a camshaft housing advance passage  59  in communication to the valve timing advance passage  57  are formed in the first camshaft housing  43 A. 
   Further, as shown in  FIG. 4 , an end journal  41 A, or a first camshaft journal at a right end of the intake camshaft  41  includes an end journal retard passage  60  in communication to the camshaft housing retard passage  58 , and an end journal advance passage  61  in communication to the camshaft housing advance passage  59 . In the end journal  41 A, only the actuator oil passage  53  is therefore formed. Thereby, the structure can be simplified. 
   The end journal retard passage  60  is communicated to a retard chamber of the actuator  48 ; the end journal advance passage  61  is communicated to an advance chamber of the actuator  48 . 
   Referring to  FIG. 1 , the cylinder head-side oil passage  52  and the second camshaft bearing section  40 B adjacent to the first camshaft bearing section  40 A in the axial direction of the intake camshaft  41  are communicated by a communication oil passage  66  of a communication passage section  65  as the camshaft bearing oil passage  54 . 
   The communication oil passage  66  is communicated to a second camshaft housing lubricating passage  64 B formed in the second camshaft housing  43 B supporting the second camshaft journal  41 B of the intake camshaft  41 . In addition, the communication oil passage  66  is formed inward of the water jacket  15 . 
   As shown in  FIG. 1 , the cylinder head  3  includes a partition wall  67  which separates the upward valve operating chamber  12  from the downward water jacket  15 . 
   Also, in the edge wall  8  of the cylinder head  3  in a section lower than the partition wall  67 , a boss section  68  of a certain area is formed which has one end joined to the chain case  7  and the other end protruding into the water jacket  15 . The boss section  68  is formed to protrude into the water jacket  15  so as to permit proper flow of the cooling water in the water jacket  15 . 
   Within the boss section  68 , a branch oil passage  69  is formed which linearly extends into the water jacket  15  from the joining surface  8 A with the chain case  7  and which has an intermediate portion to which the cylinder head-side oil passage  52  is connected. The branch oil passage  69  extends to the vicinity of the combustion chamber  9  of the water jacket  15 , that is adjacent to the ignition plug hole  10 . 
   The branch oil passage  69  toward the chain case  7  with respect to a junction with the cylinder head-side oil passage  52  forms the valve upstream-side passage section  55 A. 
   Also, an end section of the branch oil passage  69  protruding into the water jacket  15  and a camshaft cap coupling surface  70  of the second camshaft bearing section  40 B are communicated by the linear communication passage section  65 . 
   Referring to  FIG. 4 , when viewing the cylinder head  3  from a side of a mounting surface  4 A of the cylinder head cover  4 , a centerline  68 C of the boss section  68  is offset with respect to a center  11 C of the ignition plug hole wall  11  by a distance L in a direction perpendicular to the axial direction X of the camshaft (in the longitudinal direction of the vehicle) toward the axis of the intake camshaft  41  to which the actuator  48  is attached. 
   Referring to  FIG. 1 , the branch oil passage  69  is formed in a stepped shape by a first branch oil passage  71  and a second branch oil passage  72 ; a diameter D 2  of the second branch oil passage  72  at the junction with the communication oil passage  66  is reduced with respect to a diameter D 1  of the first branch oil passage  71  at the junction with the cylinder head-side oil passage  52 . 
   The first branch oil passage  71  is communicated to the oil control valve  49  through a case oil passage of the chain case  7 . 
   In this connection, as shown in  FIGS. 1 and 4 , a camshaft bearing lubrication passage  63  that extends upwardly is connected to the second branch oil passage  72  at a center portion in the axial direction thereof; the camshaft bearing lubrication passage  63  is communicated to an exhaust camshaft bearing section  73 A that supports the exhaust camshaft  42  thorough a first camshaft housing lubricating passage  73  that is formed in the first camshaft housing  43 A. 
   As shown in  FIG. 6 , the timing chain  46  is maintained under a certain tension by a forward chain guide  74  and a rearward tensioner mechanism  77  including a chain tensioner  75  and a tensioner arm  76 . 
   Operation of the first embodiment of the present invention is explained as follows. 
   The oil in the oil pan  5  is sucked by the driven oil pump  32  through the oil strainer  37 , and is pumped to the main gallery  35  in the cylinder block  2 . 
   The oil in the main gallery  35  is introduced through the cylinder block-side oil passage  36  to the cylinder head-side oil passage  52  in the cylinder head  3 . 
   The oil having been introduced to the cylinder head-side oil passage  52  is branched by the branch oil passage  69  into the actuator oil passage  53  for conducing the oil toward the chain case  7  and the camshaft bearing oil passage  54  for conducting the oil toward the first and second camshaft bearing sections  40 A,  40 B of the cylinder head  3 . 
   The oil having been introduced to the actuator oil passage  53  is divided by the oil control valve  49  into the valve timing retard passage  56  and the valve timing advance passage  57 . 
   The oil is then introduced to the retard chamber and the advance chamber of the actuator  48  for the variable valve timing mechanism  47  through the end journal advance passage  60  and the end journal advance passage  61  of the end journal  41 A of the intake camshaft  41  so as to change the timing of valve operations. 
   On the other hand, the oil having been introduced to the camshaft bearing oil passage  54  is introduced to the second camshaft journal  41 B of the intake camshaft  41  through the communication oil passage  66  and the second camshaft housing lubricating oil passage  64 B in the second camshaft housing  43 B. 
   Further, some of the oil having been introduced to the camshaft bearing oil passage  54  is introduced to the camshaft bearing section  73 A toward the exhaust camshaft  42  through the camshaft bearing lubrication passage  63  and the first camshaft housing lubricating oil passage  73  in the first camshaft housing  43 A. 
   Thereby, the lubricating oil path for the intake camshaft  41  to which the actuator  48  of the variable valve timing mechanism  47  is attached is guided to the second camshaft journal  41 B of the intake camshaft  41  by the branch oil passage  69  that extends inside the water jacket  15  of the cylinder head  3  and by the communication oil passage  66 , which simplifies the structure of the oil passage. 
   Also the branch oil passage  69  extends to the vicinity of the combustion chamber  9  of the water jacket  15 , i.e. adjacent to the ignition plug hole  10 , which brings the flow of the cooling water to the vicinity of the combustion chamber  9 , in particular the ignition plug hole wall  11 , when the cooling water introduced by the water pump  22  on the intake side flows toward the exhaust side. 
   More particularly, according to the first embodiment of the present invention, in the cylinder head  3  equipped with the variable valve timing mechanism  47 , the end journal  41 A of the intake camshaft  41  is provided with only the actuator oil passage  53  for the actuator  48  of the variable valve timing mechanism  47 ; the camshaft bearing oil passage  54  has the communication oil passage  66  formed inward of the water jacket  15  in the cylinder head  3  for conducting the oil to the second camshaft journal  41 B. Thereby, the camshaft bearing oil passage  54  is simplified while fully obtaining the operating oil pressure for the variable valve timing mechanism  47 , reducing the number of components and allowing the cylinder head  3  to be made smaller in size to downsize the engine  1  and promote productivity. Also the boss section  68  having the branch oil passage  69  therein provides proper flow of the cooling water in the cylinder head  3  to improve coolability of the combustion chamber  9  in the cylinder head  3 . 
   While the first embodiment of the present invention has been explained above, the constitution of this embodiment is applied to each claim as follows. 
   Firstly, the present invention provides the partition wall  67  which separates the upward valve operating chamber  12  from the downward water jacket  15 ; in the edge wall  8  of the cylinder head  3  in the section lower than the partition wall  67 , the boss section  68  of the certain area is formed to protrude into the water jacket  15 , which has one end joined to the chain case  7  and the other end protruding into the water jacket  15 ; within the boss section  68 , the branch oil passage  69  is formed which linearly extends into the water jacket  15  from the joining surface  8 A with the chain case  7  and which has the intermediate portion to which the cylinder head-side oil passage  52  is connected; and the valve upstream-side passage section  55 A is specified by the section of the branch oil passage  69  toward the chain case  7  with respect to the junction of the branch oil passage  69  and the cylinder head-side oil passage  52 . Also, the end section of the branch oil passage  69  protruding into the water jacket  15  and the camshaft cap coupling surface  70  of the second camshaft bearing section  40 B are communicated by the linear communication passage section  65 . 
   By such constitution, the valve upstream-side passage section  55 A that is upstream of the actuator oil passage  53  and the upstream section of the camshaft bearing oil passage  54  are integrated into the branch oil passage  69  extending linearly into the boss section  68 , which simplifies the oil passage structure of the cylinder head  3 . 
   In addition, the branch oil passage  69  is positioned at the lower level than the partition wall  67  that separates the valve operating chamber  12  in the cylinder head  3  from the water jacket  15 , and the branch oil passage  69  protrudes into the water jacket  15 , so that the camshaft cap coupling surface  70  of the second camshaft bearing section  40 B and the inner edge section of the branch oil passage  69  can be communicated by the linear communication passage section  65 , which simplifies the structure of the camshaft bearing oil passage  54 . 
   Further, this may decrease the possibility of fall or deterioration of working tools from a perpendicular direction to the camshaft cap coupling surface  70  when shaping the communication oil passage  66 , which promotes workability. 
   Also the branch oil passage  69  and the communication oil passage  66  protrude into the water jacket  15 , which simplifies the oil passage structure formed in the upper part of the edge wall  8  of the cylinder head  3  and allows the cylinder head  3  to be made smaller in size to promote the productivity. 
   Moreover, the boss section  68  causes the cooling water, which is introduced from the cooling water introducing passage  16  of the cylinder head  3  adjacent to the water pump  22  and flows in the direction perpendicular to the rows of the cylinders (in the longitudinal direction of the vehicle), to be deviated toward the center of the combustion chamber  9 , which enhances the cooling effect at the center of the combustion chamber  9 . 
   According to the invention defined in claim  2 , when viewing the cylinder head  3  from the side of the mounting surface  4 A of the cylinder head cover  4 , the centerline  68 C of the boss section  68  is offset with respect to the center of the ignition plug hole wall  11  in the direction perpendicular to the axial direction X of the camshaft (in the longitudinal direction of the vehicle) toward the axis of the intake camshaft  41  to which the actuator  48  is attached. 
   Thereby, the communication passage section  65  can be positioned adjacent to the ignition plug hole wall  11  in the axial direction X of the camshaft, which reduces the longitudinal dimension of the cylinder head  3  and reduces the entire length of the communication oil passage  66 , promoting the workability and improving the productivity of the cylinder head  3 . 
   According to the invention defined in claim  3 , the branch oil passage  69  is formed in the stepped shape; the diameter of the branch oil passage  69  at the junction with the communication oil passage  66  is reduced with respect to the diameter of the passage at the junction with the cylinder head-side oil passage  52 . 
   This is intended to enhance responsivity of the actuator  48  of the variable valve timing mechanism  47  by reducing the diameter of the branch oil passage  69  on a joint side of the communication oil passage  66  so as to supply more oil through the actuator oil passage  53 . Also, thanks to the structure of the present invention, the actuator oil passage  53  can be made greater in diameter than the camshaft bearing oil passage  54  merely by processing the branch oil passage  69  by using the cutting tools in a stepped shape, which promotes the productivity of the cylinder head  3 . 
   DETAILED DESCRIPTION OF A SECOND EMBODIMENT OF THE INVENTION 
     FIG. 8  illustrates a second embodiment of the present invention. 
   In the second embodiment, the elements identical or similar to the first embodiment are designated by the same reference numbers. 
   The second embodiment of the present invention is characterized as follows. In the edge wall  8  of the cylinder head  3 , a branch oil passage  81  is formed which is communicated to the cylinder head-side oil passage  52  and which conducts the oil toward the oil control valve  49 ; a camshaft bearing oil groove  82  is formed which is communicated to the branch oil passage  81 ; and a camshaft bearing oil passage  83  is formed which is communicated to the camshaft bearing oil groove  82 . The camshaft bearing oil groove  82  is formed to have a certain area in a width W, and functions as a throttling valve to restrict the oil required for lubricating the camshaft. The camshaft bearing oil groove  83  is formed within the water jacket  15  of the cylinder head  3 . 
   In the edge wall  8  of the cylinder head  3 , the valve timing retard passage  56  and the valve timing advance passage  57  are formed for conducting the oil from the oil control valve  49  toward the actuator  48 . 
   According to the second embodiment, the oil pumped from the cylinder block  2  is introduced to the branch oil passage  81 , and is divided at the control valve  49  into the valve timing retard passage  56  and the valve timing advance passage  57 . Also, the oil pumped from the cylinder block  2  is introduced through the camshaft bearing oil groove  82  to the camshaft bearing oil passage  83 . At this moment, the flow rate of the oil for the camshaft bearing is restricted by the camshaft bearing oil groove  82 . 
   Thereby, the camshaft bearing oil groove  82  functioning as conventional throttling valve eliminates the need for the throttling valve, reducing the number of components and simplifying the structure. 
   INDUSTRIAL APPLICABILITY 
   The present invention is illustrated for the cylinder head structure equipped with the variable valve timing mechanism. However, the present invention can be applied to the cylinder head using common materials without the variable valve timing mechanism, which is devoid of processing of oil passage such as the valve timing retard passage, the valve timing advance passage, and the camshaft bearing lubrication path. 
   EXPLANATION OF REFERENCE NUMERALS 
     1 —engine; 
     2 —cylinder block; 
     3 —cylinder head; 
     4 —cylinder head cover; 
     5 —oil pan; 
     7 —chain case; 
     9 —combustion chamber; 
     10 —ignition plug hole; 
     11 —ignition plug hole wall; 
     22 —water pump; 
     32 —oil pump; 
     35 —main gallery; 
     40 —camshaft bearing section; 
     41 —intake camshaft; 
     42 —exhaust camshaft; 
     43 —camshaft housing; 
     47 —variable valve timing mechanism; 
     48 —actuator; 
     49 —oil control valve; 
     52 —cylinder head-side oil passage; 
     53 —actuator oil passage; 
     54 —camshaft bearing oil passage; 
     55 A—valve upstream-side passage section; 
     55 B—valve downstream-side passage section; 
     56 —valve timing retard passage, 
     57 —valve timing advance passage; 
     63 —camshaft bearing lubrication passage; 
     65 —communication passage section; 
     66 —communication oil passage; 
     67 —partition wall; 
     68 —boss section; 
     69 —branch oil passage; 
     70 —camshaft cap coupling surface; and 
     73 —exhaust camshaft bearing lubrication passage.