Patent Publication Number: US-10774701-B2

Title: Internal combustion engine

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an internal combustion engine comprising: a crankcase; an oil filter that is mounted to a mounting surface formed on the crankcase and clarifies an oil flowing in; and an oil cooler that is disposed on a front side of the crankcase, cools the oil flowing in from the oil filter and returns the oil into a flow path in the crankcase. 
     Description of the Related Art 
     Japanese Patent Application Laid-open No. 2006-97613 discloses an internal combustion engine having an oil filter mounted to a mounting surface of a crankcase. The mounting surface is formed at a bottom plate of the crankcase on the front side of an oil pan. The oil filter is mounted to the mounting surface from below. 
     An oil cooler is disposed on the front side of the crankcase. An outflow port through which an oil flows out toward the oil cooler and an inflow port through which the oil flows in from the oil cooler are disposed at a front wall of the crankcase. Since the outflow port and the inflow port for the oil are disposed at a distance from the oil filter, the routes of oil passages would be complicated. Attendant on the complication of the routes of the oil passages, the number of working steps at the time of manufacturing the crankcase would be increased. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished in light of the above circumstances, and it is an object thereof to provide an internal combustion engine in which the routes of oil passages can be simplified as much as possible. 
     According to a first aspect of the present invention, there is provided an internal combustion engine comprising: a crankcase; an oil filter that is mounted to a mounting surface formed on the crankcase and clarifies an oil flowing in; and an oil cooler that is disposed on a front side of the crankcase, cools the oil flowing in from the oil filter and returns the oil into a flow path in the crankcase, wherein the internal combustion engine further comprises a bracket formed on a front wall of the crankcase and having the mounting surface, and an outflow port through which the oil flows out toward the oil cooler and an inflow port through which the oil flows in from the oil cooler are disposed in the bracket. 
     In accordance with the first aspect, the oil passages interconnecting the crankcase and the oil cooler are concentratedly disposed in the bracket, and, therefore, the routes of the oil passages can be simplified. At the time of forming the crankcase, the number of working steps in processing the oil passages can be reduced as much as possible. 
     According to a second aspect of the present invention, in addition to the first aspect, the bracket has the mounting surface receiving the oil filter that protrudes forward from the front wall of the crankcase, the oil filter being attached and detached in an up-down direction. 
     In accordance with the second aspect, interference between the oil filter and the oil cooler can be avoided, as compared to the case where the oil filter is attached to and detached from the mounting surface formed at the front wall of the crankcase, in the front-rear direction. Maintainability such as replacement of the oil filter can be secured to be good. 
     According to a third aspect of the present invention, in addition to the first or second aspect, there is provided the internal combustion engine, further comprising a casing that is formed at the front wall of the crankcase and accommodates a balancer operatively connected with rotation of a crankshaft, and the casing protrudes from the front wall of the crankcase in parallel to the oil filter. 
     In accordance with the third aspect, the oil filter and the casing are arranged in parallel to each other on the front side of the crankcase, and, therefore, the internal combustion engine is reduced in size in the front-rear direction. 
     According to a fourth aspect of the present invention, in addition to the third aspect, the crankcase is provided with a branch oil passage that is branched from an oil passage extending from the oil filter toward the outflow port, the branch oil passage supplying the oil to the balancer. 
     In accordance with the fourth aspect, the supply of the oil to the balancer can be realized through a short oil passage from the oil filter. 
     According to a fifth aspect of the present invention, in addition to the first or second aspect, the oil cooler is disposed under a radiator, and has a first port communicating with the outflow port and a second port communicating with the inflow port, between a first horizontal plane making contact with the oil filter from above and a second horizontal plane making contact with the oil filter from below. 
     In accordance with the fifth aspect, the piping interconnecting the crankcase and the oil cooler can be shortened as much as possible. 
     According to a sixth aspect of the present invention, in addition to the first or second aspect, the oil filter is located within a transverse width of the oil cooler as seen in front view, and part of the oil filter is located within an up-down width of the oil cooler as seen in front view. 
     In accordance with the sixth aspect, when the internal combustion engine is mounted on a two-wheeled motor vehicle, the influence of flying stones and the like coming from the front side on the oil filter during traveling of the two-wheeled motor vehicle can be reduced. 
     According to a seventh aspect of the present invention, in addition to the first or second aspect, the flow path includes: a main gallery that extends in parallel to a rotational axis of a crankshaft and apportions the oil in the crankcase; a first linear oil passage that is connected to the inflow port and extends linearly from an outer surface of the bracket to intersect the main gallery; and a second linear oil passage that is connected to an oil pump, extends linearly in parallel to the first linear oil passage, and opens into the oil filter. 
     In accordance with the seventh aspect, the first linear oil passage and the second linear oil passage are concentratedly disposed in the periphery of the oil filter. Therefore, a processing work is made efficient, and productivity is enhanced. Especially, since the first linear oil passage and the second linear oil passage extend in parallel to each other, the processing work can be realized from the same direction, and the working process can be made more efficient. 
     The above and other objects, characteristics and advantages of the present invention will be clear from detailed descriptions of the preferred embodiment which will be provided below while referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view schematically depicting a whole configuration of a two-wheeled motor vehicle according to an embodiment of the present invention. 
         FIG. 2  is a side view schematically depicting the whole configuration of the two-wheeled motor vehicle in a state in which a body cover has been detached. 
         FIG. 3  is an enlarged partial side view of an internal combustion engine including an oil cooler. 
         FIG. 4  is an enlarged front view of an engine main body. 
         FIG. 5  is an enlarged front view of the internal combustion engine including a radiator and the oil cooler. 
         FIG. 6  is an enlarged vertical sectional view of the engine main body as observed in a section orthogonal to a rotational axis of a secondary balancer. 
         FIG. 7  is an enlarged partial sectional view of the internal combustion engine as observed in a section including a rotational axis of a crankshaft and a cylinder axis. 
         FIG. 8  is an enlarged partial sectional view of the internal combustion engine as observed in a vertical section including a center axis of an oil filter and an axis of a balancer shaft. 
         FIG. 9  is an enlarged partial sectional view of the internal combustion engine as observed in a horizontal section including an axis of a balancer shaft. 
         FIG. 10  is an enlarged partial sectional view of the internal combustion engine as observed in a horizontal section including a center axis of a main gallery. 
         FIG. 11  is an enlarged vertical sectional view of the internal combustion engine as observed in a section orthogonal to a rotational axis of an oil pump. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be described below, referring to the attached drawings. Here, the directions of up, down, front, rear, left and right of a vehicle body are to be defined based on the gaze of a rider riding a two-wheeled motor vehicle. 
       FIG. 1  denotes schematically a whole image of a two-wheeled motor vehicle which is a saddle type vehicle according to an embodiment of the present invention. A two-wheeled motor vehicle  11  includes a body frame  12 , and a body cover  13  mounted to the body frame  12 . The body cover  13  includes a front cowl  14  covering the body frame  12  from the front side, and a tank cover  17  which continues forward from an outer surface of a fuel tank  15  and is connected to a rider seat  16  on the rear side of the fuel tank  15 . A fuel is reserved in the fuel tank  15 . The rider straddles the rider seat  16  when driving the two-wheeled motor vehicle  11 . 
     The body frame  12  includes: a head pipe  18 ; a pair of left and right main frames  21  that extend rearwardly downward from the head pipe  18  and have pivot frames  19  at rear lower ends thereof; a down frame  22  that extends downward from the head pipe  18  at a position under the main frames  21  and is united to the main frames  21 ; and left and right seat frames  23  that extend rearwardly upward from curved regions  21   a  of the main frames  21  and constitute a truss structure. The rider seat  16  is supported on the seat frames  23 . 
     A front fork  24  is steerably supported on the head pipe  18 . A front wheel WF is supported on the front fork  24  such as to be rotatable around an axle  25 . A steering handlebar  26  is connected to an upper end of the front fork  24 . When driving the two-wheeled motor vehicle  11 , the driver holds grips at left and right ends of the steering handlebar  26 . 
     A swing arm  28  is linked to the body frame  12  on the rear side in the vehicle, such as to be swingable in the up-down direction around a pivot  27 . A rear wheel WR is supported on a rear end of the swing arm  28  such as to be rotatable around an axle  29 . An internal combustion engine  31  producing a driving force that is to be transmitted to the rear wheel WR is mounted on the body frame  12  between the front wheel WF and the rear wheel WR. The internal combustion engine  31  is supported in the state of being linked to the down frame  22  and the main frames  21 . Power of the internal combustion engine  31  is transmitted to the rear wheel WR through a transmission device. 
     As depicted in  FIG. 2 , an engine main body of the internal combustion engine  31  includes a crankcase  33  that has, at an upper end and a lower end of a rear wall, internal combustion engine hangers  32   a  and  32   b  linked to the main frames  21  and outputs the power around a rotational axis Rx; a cylinder block  34  that is connected to a front portion of the crankcase  33  from above and has a cylinder axis C located in a vertical plane orthogonal to the rotational axis Rx and rising relative to a horizontal plane; a cylinder head  35  that is connected to an upper end of the cylinder block  34 , has at a front wall an internal combustion engine hanger  32   c  linked to the down frame  22 , and support a valve train; and a head cover  36  that is connected to an upper end of the cylinder head  35  and covers the valve train over the cylinder head  35 . 
     An intake system  38  that sprays fuel to air clarified by an air cleaner  37  to form an air-fuel mixture and supplies the air-fuel mixture into a combustion chamber covered by the cylinder head  35 , and an exhaust system  41  that clarifies, by a catalyst  39 , an exhaust gas after combustion discharged from the combustion chamber and discharges the exhaust gas to the rear side of the vehicle body while lowering the temperature of the exhaust gas, are connected to the cylinder head  35 . The exhaust system  41  has an exhaust pipe  42  which extends under the crankcase  33  along a lateral side of the rear wheel WR and supports the catalyst  39  under the crankcase  33 . 
     The internal combustion engine  31  includes: a cooling device  44  that causes cooling water to flow between a radiator  43  disposed on the front side of the cylinder block  34  and a water jacket in the engine main body to realize cooling of the engine main body; and an oil circulation device  46  that causes an engine oil to flow between an oil cooler  45  disposed on the front side of the crankcase  33  and linked to a lower end of the radiator  43  and a flow path in the engine main body, so as to realize cooling of the engine oil. An upper end of the radiator  43  is fastened to the down frame  22 . As depicted in  FIG. 3 , a lower end of the radiator  43  is linked to a front wall of the crankcase  33  by a first stay  47 . An attachment piece  48  fastened to the lower end of the radiator  43  is fixed to an upper end of the oil cooler  45 . An attachment piece  51  fastened to a front end of a second stay  49  extending from the front wall of the crankcase  33  is fixed to a lower end of the oil cooler  45 . 
     The oil circulation device  46  includes an oil filter  53  that is mounted from below to a mounting surface  52  formed on the crankcase  33  and clarifies the engine oil flowing in. The oil filter  53  has a filter element accommodated in a cylindrical container having a center axis extending in the vertical direction. The mounting surface  52  for the oil filter  53  is formed in a downward orientation on a bracket  54  protruding from the front wall of the crankcase  33 . The oil filter  53  is attached to and detached from the bracket  54  in the up-down direction. 
     The oil cooler  45  includes: a first joint  56  that is connected to a first connection pipe  55  extending from the front wall of the crankcase  33  and has a first port  56   a  for accepting the engine oil flowing out of the crankcase  33 ; and a second joint  58  that is connected to a second connection pipe  57  extending from the front wall of the crankcase  33  and has a second port  58   a  through which the engine oil flows out toward the crankcase  33 . The first port  56   a  and the second port  58   a  are disposed between a first horizontal plane Hf making contact with the oil filter  53  from above and a second horizontal plane Hs making contact with the oil filter  53  from below. The oil cooler  45  cools the engine oil flowing in from the oil filter  53  and returns the engine oil into an oil passage in the crankcase  33 . 
     As illustrated in  FIG. 4 , an outflow port  59  which is connected to the first connection pipe  55  and through which the engine oil flows out toward the oil cooler  45  and an inflow port  61  which is connected to the second connection pipe  57  and through which the engine oil flows in from the oil cooler  45  are disposed in the bracket  54 . Here, the bracket  54  includes a bulging part where the mounting surface  52  is formed, and a part which is continuous with the bulging part and protrudes from the front wall of the crankcase  33 . 
     The first connection pipe  55  and the second connection pipe  57  are formed by using a metallic pipe extending in a combination of the transverse vehicle direction and the longitudinal vehicle direction while bending at at least two locations, and a flexible rubber-made connection tube  62  incorporated at an intermediate point in the metallic pipe. The connection tube  62  absorbs positional deviations of the first port  56   a  and the second port  58   a  of the oil cooler  45  in relation to the outflow port  59  and the inflow port  61  of the crankcase  33 . As depicted in  FIG. 5 , as seen in front view, the oil filter  53  is located within the transverse width of the oil cooler  45 , and part of the oil filter  53  is located within the up-down width of the oil cooler  45 . The radiator  43  and the oil cooler  45  are disposed on the front side of the oil filter  53 . As seen in front view, the radiator  43  and the oil cooler  45  hide the oil filter  53 . 
     As depicted in  FIG. 6 , the cylinder block  34  is formed therein with cylinders  64  each of which guides a linear reciprocating motion of a piston  63  along the cylinder axis C. Here, the internal combustion engine  31  is a so-called in-line four-cylinder engine in which four cylinders  64  are arranged along the rotational axis Rx in the cylinder block  34 . A combustion chamber  65  is defined between the piston  63  and the cylinder head  35 . By the functions of an intake valve  66   a  and an exhaust valve  66   b  opened and closed according to rotation of a camshaft, an air-fuel mixture is introduced into the combustion chamber  65  and an exhaust gas after combustion is discharged from the combustion chamber  65 . 
     The crankcase  33  includes an upper body  67   a  and a lower body  67   b  split at a split surface defined in a horizontal plane Dp, and an oil pan  67   c  connected from below to the lower body  67   b  at a mating surface  68  defined in an imaginary plane Mp intersecting the horizontal plane Dp, which contains the split surface, at a predetermined inclination angle. An intersection between the imaginary plane Mp and the horizontal plane Dp is set in parallel to the rotational axis Rx of a crankshaft. The mating surface  68  is inclined rearwardly downward from a front edge thereof. 
     As illustrated in  FIG. 7 , the crankshaft  71  is supported on the crankcase  33  such as to be rotatable around the rotational axis Rx. The crankshaft  71  includes journals  72  formed coaxially with the rotational axis Rx, and cranks  74  which are each disposed between the adjacent journals  72  and which each have a crank pin  73  extending in parallel to the rotational axis Rx and interconnecting crank webs. The crankcase  33  is formed with partition walls  75  individually supporting the journals  72  rotatably by plain bearings correspondingly to the individual cylinders  64 . A large end portion of a connecting rod  76  extending from the piston  63  is rotatably linked to the crank pin  73 . The connecting rod  76  convers the linear reciprocating motion of the piston  63  into a rotational motion of the crankshaft  71 . 
     One end of the crankshaft  71  protrudes to the outside from a left side surface of the crankcase  33 . An alternating current generator (ACG)  77  is connected to the one end of the crankshaft  71 . An ACG cover  78  for accommodating the ACG  77  between itself and the crankcase  33  is connected to the left side surface of the crankcase  33 . 
     The other end of the crankshaft  71  protrudes to the outside from a right side surface of the crankcase  33 . A valve train  79  that transmits power to the camshaft is linked to the other end of the crankshaft  71 . A valve train cover  81  for partly accommodating the valve train  79  between itself and the crankcase  33  is connected to the right side surface of the crankcase  33 . The ACG cover  78  and the valve train cover  81  cover an outer surface of the crankcase  33  to define a crank chamber CR for accommodating the crankshaft  71 . 
     As depicted in  FIG. 6 , a secondary balancer  82  disposed on the front side of the crankshaft  71  and operatively connected with the crankshaft  71  is accommodated in the crankcase  33 . The secondary balancer  82  includes an eccentric weight  84  supported on a balancer shaft  83  rotatably around an axis parallel to the rotational axis Rx of the crankshaft  71 , and a balancer driven gear  85   a  supported on the balancer shaft  83  rotatably coaxially with the eccentric weight  84  and linked to the eccentric weight  84 . The balancer driven gear  85   a  may be supported on and fixed to the eccentric weight  84 . The balancer driven gear  85   a  is meshed with a driving gear  85   b  fixed to the crankshaft  71 . By receiving the driving force of a driving gear  85   b , the balancer driven gear  85   a  causes rotation of the eccentric weight  84  around the balancer shaft  83 . As illustrated in  FIG. 7 , the driving gear  85   b  is formed to be integral with one of the cranks  74  of the crankshaft  71 . 
     As depicted in  FIG. 4 , the front wall of the crankcase  33  is formed with a casing  86  which defines a space for accommodating the eccentric weight  84  and the balancer driven gear  85   a , continuously from the crank chamber CR. As illustrated in  FIG. 8 , the crankcase  33  is formed with a wall body  87  for accommodating the ACG  77  between itself and the ACG cover  78 , continuously from the partition walls  75 . 
     The casing  86  includes: a first casing wall  89  that faces the wall body  87  with a space  88  therebetween while contacting the front wall of the crankcase  33 , at a position separate from the wall body  87  in the axial direction of the crankshaft  71 ; and a second casing wall  91  that is faced to the first casing wall  89  with the accommodation space for the eccentric weight  84  and the balancer driven gear  85   a  therebetween. The first casing wall  89  is continuous from the partition wall  75  disposed between the cylinder  64  located on an outer side and the cylinder  64  located on an inner side. The second casing wall  91  is continuous from the partition wall  75  disposed between the cylinders  64  located on the inner side. 
     The balancer shaft  83  has, at one end and the other end thereof, a first support shaft  92   a  and a second support shaft  92   b  which have an axis parallel to the rotational axis Rx of the crankshaft  71  and eccentric from the rotational axis of the eccentric weight  84 . The first support shaft  92   a  is inserted in and supported by a support hole  93  bored in the first casing wall  89 . The second support shaft  92   b  is inserted in and supported by a support hole  94  bored in the second casing wall  91 . 
     The one end of the balancer shaft  83  protrudes from the first casing wall  89  into the space  88 , and is faced to the wall body  87  at its tip end. The eccentric weight  84  is mounted to an eccentric shaft  96  through a rolling bearing. When the balancer shaft  83  rotates, the balancer driven gear  85   a  can be brought toward and away from the driving gear  85   b  by the function of the eccentric shaft  96 . Backlash is controlled between the balancer driven gear  85   a  and the driving gear  85   b.    
     The wall body  87  is formed therein with a through-hole  97  having a diameter larger than the outside diameter of the balancer shaft  83 , coaxially with the first support shaft  92   a  of the balancer shaft  83 . The through-hole  97  has a large diameter portion on the ACG  77  side. A plug member  98  for closing the through-hole  97  is inserted into the large diameter portion of the through-hole  97  in a liquid-tight manner, from outside of the crankcase  33 . The generator cover  78  is formed with a retainer  99  that makes contact with the plug member  98  when the generator cover  78  is connected to the crankcase  33  from outside of the crankcase  33 . 
     At the crankcase  33 , the bracket  54  is united to the casing  86 . The bracket  54  is formed therein with a vertical oil passage  101  (as an oil passage) extending linearly in the vertical direction from the oil filter  53 , and a horizontal oil passage  103  (as an oil passage) that extends linearly in a horizontal direction from an upper end of the vertical oil passage  101  and is connected to an in-shaft oil passage  102  coaxially bored in the balancer shaft  83 . The engine oil is supplied from the in-shaft oil passage  102  to a rolling bearing on the eccentric shaft  96 . 
     As illustrated in  FIG. 9 , in the bracket  54 , an outlet oil passage  104  is defined which is connected to the upper end of the vertical oil passage  101 , extends linearly, and is connected to the outflow port  59 . The vertical oil passage  101  and the outlet oil passage  104  form an oil passage which extends from the oil filter  53  toward the outflow port  59 . Therefore, the horizontal oil passage  103  functions as a branch oil passage. 
     As depicted in  FIG. 10 , the crankcase  33  is formed therein with a main gallery  105  that extends in parallel to the rotational axis Rx of the crankshaft  71  and penetrates the individual partition walls  75 . The bracket  54  is formed therein with a first linear oil passage  106  that extends linearly from an outer surface of the bracket  54  to intersect the main gallery  105 , and a second linear oil passage  107  that extends in parallel to the first linear oil passage  106  and opens into the oil filter  53 . An inlet oil passage  108  that extends linearly from the outer surface of the bracket  54 , intersects the first linear oil passage  106  at a small inclination angle and is connected to the inflow port  61  is connected to the first linear oil passage  106 . An opening end (front end) of the first linear oil passage  106  and an opening end (front end) of the second linear oil passage  107  are each closed in a liquid-tight manner by a plug member  109 . 
     As illustrated in  FIG. 11 , the oil circulation device  46  includes an oil pump  111  that is mounted inside the crankcase  33  and is operated in operative connection with the rotation of the crankshaft  71 . The oil pump  111  is configured as a trochoid pump. Specifically, the oil pump  111  includes: a pump chamber  112  defining a disk-shaped space having an axis parallel to the rotational axis Rx of the crankshaft  71 ; an outer rotor  113  that is fitted to the pump chamber  112  such as to be slidable on an inner wall surface of the pump chamber  112  at a cylindrical surface coaxial with the pump chamber  112 ; and an inner rotor  114  that is disposed inside the outer rotor  113  and is rotated around a rotational axis deviated from a rotational axis of the outer rotor  113 . 
     The oil pump  111  is provided with a downwardly directed suction port  115  for sucking up the engine oil from a lower position of an oil pan  67   c . A strainer  116  extending to the lower position of the oil pan  67   c  is connected to the suction port  115 . When the oil pump  111  operates, the engine oil reserved in the oil pan  67   c  is sucked into the pump chamber  112  via the suction port  115 . 
     The oil pump  111  is provided with a downwardly directed discharge port  117 . An oil pipe  118  that extends forwardly upward and is connected to the bracket  54  from inside of the crankcase  33  is connected to the discharge port  117 . As depicted in  FIG. 10 , the second linear oil passage  107  in the bracket  54  is connected to the oil pump  111  through the oil pipe  118 . 
     As illustrated in  FIG. 11 , each of the partition walls  75  is formed with a supply oil passage  119  rising linearly in the longitudinal direction from the main gallery  105 . An upper end of the supply oil passage  119  opens to each plain bearing. In this way, the engine oil is apportioned in the crankcase  33  from the main gallery  105 . 
     As depicted in  FIG. 8 , the crankcase  33  is formed with a connection oil passage  121  extending linearly in the longitudinal direction from the first linear oil passage  106 . An apportioning oil passage  122  extending linearly in parallel to the rotational axis Rx of the crankshaft  71  is connected to an upper end of the connection oil passage  121 . The apportioning oil passage  122  is formed with piston oil jets  123  on the basis of each of the cylinders  64 . The engine oil is jetted from the piston oil jets  123  to the pistons  63  in the cylinders  64 . 
     An operation of the present embodiment will be described below. When the crankshaft  71  rotates, the inner rotor  114  and the outer rotor  113  are rotated in the pump chamber  112  in operative connection with the rotation of the crankshaft  71 . According to variations in the internal volume, the engine oil is sucked into the pump chamber  112  via the suction port  115 , and is discharged through the discharge port  117 . The engine oil flows from the discharge port  117  through the oil pipe  118  into the second linear oil passage  107 . The engine oil flows through the second linear oil passage  107  into the oil filter  53 . In the oil filter  53 , the engine oil flows from an outer periphery through the filter element to be thereby clarified, and flows into the vertical oil passage  101  in the bracket  54 . The engine oil flows through the vertical oil passage  101  and the outlet oil passage  104 , and flows into the first connection pipe  55  via the outflow port  59 . The engine oil flows through the first port  56   a  of the first joint  56  into the oil cooler  45 , to be cooled. 
     Simultaneously, the engine oil flows into the horizontal oil passage  103  branched from the vertical oil passage  101 . The engine oil flows through the horizontal oil passage  103  into the in-shaft oil passage  102  in the balancer shaft  83 . The engine oil is supplied from the in-shaft oil passage  102  to the rolling bearing on the eccentric shaft  96 . Since cooling is not so required at the balancer shaft  83 , the function of the engine oil is sufficiently secured even when the engine oil before cooling is supplied. The engine oil flowing out from the rolling bearing flows into the oil pan  67   c  via the casing  86 . Since the bracket  54  protrudes forward from the front wall of the crankcase  33 , the engine oil can be air-cooled in the vertical oil passage  101 , the horizontal oil passage  103 , and the outlet oil passage  104 . 
     The engine oil after cooling flows from the second port  58   a  of the second joint  58  through the second connection pipe  57 , and flows into the inlet oil passage  108  via the inflow port  61 . The engine oil flows from the inlet oil passage  108  through the first linear oil passage  106  and the main gallery  105 , to be supplied to the plain bearings on the basis of each of the partition walls  75 . Between the crankshaft  71  and the plain bearings, friction is moderated by the function of the engine oil. The engine oil flowing out from the plain bearings flows into the oil pan  67   c.    
     The engine oil branches from the first linear oil passage  106  into the connection oil passage  121 . The engine oil flows from the connection oil passage  121  through the apportioning oil passage  122 , to be jetted from the piston oil jets  123 . In this way, the pistons  63  are lubricated on the basis of each of the cylinders  64 . The engine oil having thus contributed to lubrication flows into the oil pan  67   c.    
     In the internal combustion engine  31  according to the present embodiment, the bracket  54  formed at the front wall of the crankcase  33  is formed with the mounting surface  52  for receiving the mounting of the oil filter  53  from below. In addition, the outflow port  59  through which the oil flows out toward the oil cooler  45  and the inflow port  61  through which the oil flows in from the oil cooler  45  are disposed in the bracket  54 . Since the oil passages interconnecting the crankcase  33  and the oil cooler  45  are concentratedly disposed in the bracket  54 , the routes of the oil passages are simplified. At the time of forming the crankcase  33 , the number of working steps in processing the oil passages is reduced as much as possible. 
     Particularly, the bracket  54  has the mounting surface  52  that receives the oil filter  53  attached and detached in the up-down direction, the mounting surface  52  protruding forward from the front wall of the crankcase  33 . Interference between the oil filter  53  and the oil cooler  45  is avoided, as compared to the case where the oil filter  53  is attached to and detached from a mounting surface formed at the front wall of the crankcase  33 , in the front-rear direction. Maintainability such as replacement of the oil filter  53  is secured to be good. 
     In the present embodiment, the casing  86  accommodating the eccentric weight  84  and the balancer driven gear  85   a  protrudes from the front wall of the crankcase  33  in parallel to the oil filter  53 . Since the oil filter  53  and the casing  86  are arranged in parallel on the front side of the crankcase  33 , the internal combustion engine  31  is reduced in size in the front-rear direction. 
     In the bracket  54  of the crankcase  33 , the branch oil passage for supplying the engine oil to the secondary balancer  82  is provided, the branch oil passage branching from the oil passage extending from the oil filter  53  toward the outflow port  59 . The supply of the oil to the secondary balancer  82  is realized through a short oil passage from the oil filter  53 . 
     In the present embodiment, the oil cooler  45  is disposed under the radiator  43 , and the first port  56   a  communicating with the outflow port  59  and the second port  58   a  communicating with the inflow port  61  are provided between the first horizontal plane Hf making contact with the oil filter  53  from above and the second horizontal plane Hs making contact with the oil filter  53  from below. The first connection pipe  55  and the second connection pipe  57  for interconnecting the crankcase  33  and the oil cooler  45  are shortened as much as possible. 
     The oil filter  53  is located within the transverse width of the oil cooler  45  as seen in front view, and part of the oil filter  53  is located within the vertical width of the oil cooler  45  as seen in front view. The oil filter  53  is hidden behind the radiator  43  and the oil cooler  45  as seen in front view. As a result, the oil filter  53  is protected from flying stones and the like coming from the front side during traveling of the two-wheeled motor vehicle  11 . 
     The engine oil flow path formed in the crankcase  33  includes: the main gallery  105  that extends in parallel to the rotational axis Rx of the crankshaft  71  and apportions the oil in the crankcase  33 ; the first linear oil passage  106  that is connected to the inflow port  61  and extends linearly from an outer surface of the bracket  54  to intersect the main gallery  105 ; and the second linear oil passage  107  that extends linearly in parallel to the first linear oil passage  106  and opens into the oil filter  53 . Since the first linear oil passage  106  and the second linear oil passage  107  are concentratedly disposed in the periphery of the oil filter  53 , a processing work is made efficient and productivity is enhanced. Especially, since the first linear oil passage  106  and the second linear oil passage  107  extend in parallel to each other, the processing work can be realized from the same direction, and the working process is made more efficient.