Patent Publication Number: US-6666183-B2

Title: V-type internal combustion engine

Description:
BACKGROUND OF THE INVENTION 
     The present invention claims the benefit of Japanese Patent Application No. 2000-387707, filed Dec. 20, 2000, the entirety of which is hereby incorporated by reference. 
     1. Field of the Invention: 
     The present invention relates to a V-type internal combustion engine having a breather apparatus for recirculating blowby gas from a crankcase to an intake system. In particular, the present invention relates to the arrangement of a breather path constituting the breather apparatus. 
     2. Description of Background Art: 
     A V-type internal combustion engine having a breather apparatus for recirculating blowby gas to an intake system has been disclosed in Japanese Utility Model Publication No. 7209/1989. The breather apparatus is provided with a breather chamber provided at a bottom wall portion of a V-bank. A hole communicates the crankcase with the breather chamber. Furthermore, a communication path is formed at a cylinder wall of the cylinder block for communicating the breather chamber and a valve operating chamber, which is in communication with an intake manifold. Accordingly, blowby gas from the crankcase is recirculated to the intake manifold via the breather chamber, the communication path and the valve operating chamber. 
     In addition, according to the conventional breather apparatus, the communication path, which is also a breather path for flowing blowby gas, is formed in the cylinder wall on an inner side of the V-bank. Therefore, a flow path area of the communication path is limited. Accordingly, in order to ensure a sufficient flow path area, a plurality of communication paths are formed. Alternatively, in order to increase the flow path area of the communication path, it is necessary to significantly bulge the cylinder wall formed with the communication path toward the inner side of the V-bank. Therefore, a width of the bank formed with the communication path is increased in a direction orthogonal to a direction of arrangement of the cylinders, increasing the size of the cylinder block and restricting the arrangement of an intake apparatus in a space formed by the V-bank. Accordingly, the internal combustion engine is increased in size 
     SUMMARY OF THE INVENTION 
     The present invention has been carried out in view of such a situation and it is an object thereof to provide a V-type internal combustion engine capable of forming a breather path having a sufficiently large flow path area without enlarging the cylinder block. 
     According to a first aspect of the present invention, a V-type internal combustion engine includes a breather apparatus for recirculating blowby gas from a crankcase to an intake system. A crankshaft having three or more crankpins includes a first, a second and a third crankpin contiguous with each other in a direction of a rotational axis line thereof. A cylinder block is formed with a first and a second bank which form a V-like shape. The first and the third crankpins are respectively connected with a first and a third connecting rod, respectively connected to a first and a third piston, respectively fitted to a first and a third cylinder bore formed at the first bank. The second crankpin is disposed between the first and the third crankpins, is connected only with a second connecting rod, connected to a second piston, fitted to a second cylinder bore formed at the second bank. Furthermore, the breather apparatus includes a breather path formed at a space portion between the first and the third cylinder bores in the first bank. 
     According to the first aspect of the present invention, in the first bank, the space portion formed between the first and the third cylinder bores which constitutes a position opposed to the second cylinder bore of the second bank, is provided with a minimum width in the direction of the rotational axis line to a degree slightly smaller than a diameter of the second cylinder bore. Therefore, a flow path area of the breather path formed at the space portion can be sufficiently increased without increasing a width of the first bank in the direction of the rotational axis line and a width in a direction orthogonal to an assumed plane including the rotational axis line and a center line of the first cylinder bore or the third cylinder bore. Accordingly, a width of the cylinder block in the direction of the rotational axis line is not increased. 
     As a result, in the first bank, the breather path is formed at the space portion having a minimum width in the direction of the rotational axis line to the degree slightly smaller than the diameter of the second cylinder bore. Therefore, the breather path having a sufficiently large flow path area is provided without enlarging the first bank in the direction of the rotational axis line and in the direction orthogonal to the assumed plane. Accordingly, the cylinder block is not enlarged and the weight of the cylinder block is reduced. Furthermore, by increasing the flow path area of the breather path, a flow rate of blowby gas flowing through the breather path can be kept to a minimum. Therefore, separation of lubricating oil mist mixed in the blowby gas is expedited. 
     According to a second aspect of the present invention, there is provided a V-type internal combustion engine having an odd number of cylinders including a breather apparatus for recirculating blowby gas from a crankcase to an intake system. A crankshaft having a plurality of crankpins includes a first and a second crankpin contiguous with each other in a direction of a rotational axis line thereof. A cylinder block is formed with a first bank having an odd number of cylinders and a second bank having an even number of cylinders which form a V-like shape. The first crankpin is connected with a first and a second connecting rod, respectively connected to a first and a second piston, respectively fitted to a first and a second cylinder bore, respectively formed at the first and the second banks. The second crankpin is connected only with a third connecting rod, connected to a third piston, fitted to a third cylinder bore, formed in a bank having a larger number of the cylinders. The breather apparatus includes a breather path formed at a space portion contiguous with the same side at which the second crankpin is contiguous to the first crankpin relative to the first cylinder bore in the bank having a smaller number of the cylinders. 
     According to the second aspect of the present invention, in the bank having the smaller number of the cylinders, the space portion contiguous with the first cylinder bore or the second cylinder bore disposed at a position opposed to the third cylinder bore of the bank having the larger number of the cylinders, is provided with a width in the direction of the rotational axis line to a degree slightly smaller than a diameter of the third cylinder bore within a range such that the bank having the smaller number of cylinders does not project to the bank having the larger number of the cylinders in the direction of the rotational axis line. A flow path area of the breather path formed at the space portion can sufficiently be increased without increasing a width of the bank having the smaller number of the cylinders in a direction orthogonal to an assumed plane including the rotational axis line and a center line of the first cylinder bore or the second cylinder bore. Accordingly, a width of the cylinder block in the direction of the rotational axis line is not increased. Furthermore, the width in the direction of the rotational axis line is reduced by coupling the two connecting rods to the first crankpin. 
     As a result, in the bank having the smaller number of cylinders, the breather path is formed at the space portion having the width in the direction of the rotational axis line to a degree slightly smaller than the diameter of the third cylinder bore within the width in the direction of the rotational axis line of the bank having the larger number of cylinders. Therefore, a breather path having a sufficiently large flow path area is provided without enlarging the bank having the smaller number of cylinders in the direction orthogonal to the assumed plane including the rotational axis line and the center line of the cylinder bore. Accordingly, the advantage of the cylinder block being downsized by coupling the two connecting rods to the first crankpin is not deteriorated. Furthermore, by increasing the flow path area of the breather path, a flow rate of blowby gas flowing in the breather path can be kept to a minimum and therefore, the separating of lubricating oil mist mixed in the blowby gas can be expedited. 
     According to a third aspect of the present invention, there is provided the V-type internal combustion engine according to the second aspect of the present invention, wherein the crankshaft includes a third crankpin contiguous with a side opposed to the side at which the first crankpin is contiguous with the second crankpin. The third crankpin is connected with a fourth and a fifth connecting rod, respectively connected to a fourth and a fifth piston, respectively connected to a fourth and fifth cylinder bore, respectively formed at the first and the second banks. Furthermore, the space portion is present between the first and the fourth cylinder bores or between the second and the fifth cylinder bores. 
     According to the third aspect of the present invention, in the bank having the smaller number of cylinders, the space portion formed between the first and the fourth cylinder bores or between the second and the fifth cylinder bores, is provided with a minimum width in the direction of the rotational axis line to a degree slightly smaller than the diameter of the third cylinder bore and within the range of a width of the bank having the larger number of cylinders in the direction of the rotational axis line. Therefore, the flow path area of the breather path formed at the space portion can be sufficiently increased without increasing the width of the bank having the smaller number of cylinders in the direction of the rotational axis line and accordingly, without increasing the width of the cylinder block in the direction of the rotational axis line, the width in the direction of the rotational axis line being reduced by coupling the two connecting rods to each of the first and the third crankpins. 
     As a result, in addition to the advantages according to the second aspect of the present invention, a breather path having a sufficiently large flow path area is provided without enlarging the bank having the smaller number of cylinders in the direction of the rotational axis line and accordingly, without deteriorating the advantage of the cylinder block being downsized by coupling the two connecting rods to each of the first and the third crankpins. Furthermore, the weight of the cylinder block is reduced. 
     According to a fourth aspect of the present invention, in the V-type internal combustion engine according to any one of the first through third aspects of the present invention, the space portion is formed with a return path for lubricating oil and a partition wall is provided between the breather path and the return path such that the breather path and the return oil path are in parallel with each other in the direction of the rotational axis line. 
     According to the fourth aspect of the present invention, the space portion is provided with a minimum width in the direction of the rotational axis line to a degree slightly smaller than the diameter of the cylinder bore within a range such that the bank having the smaller number of cylinders does not project to the bank having the larger number of cylinders in the direction of the rotational axis line. In addition, the return path for lubricating oil having a sufficiently large flow path area can be formed in addition to the breather path having a sufficient blow path area without enlarging the cylinder block. Furthermore, the blowby gas and the lubricating oil can be prevented from mixing together by the partition wall, which partitions the breather path and the return oil path to be in parallel with each other in the direction of the rotational axis line. 
     As a result, the breather path and the return oil path are formed at the space portion having a minimum width in the direction of the rotational axis line to a degree slightly smaller than the diameter of the cylinder bore such that they do not project in the direction of the rotational axis line relative to the bank having the larger number of cylinders. Accordingly, the return oil path having a sufficient flow path area is provided along with the breather path without enlarging the cylinder block and the lubricating oil therefore returns smoothly. Furthermore, the blowby gas and the lubricating oil can be prevented from mixing together by the partition wall and an amount of the lubricating oil mist mixed into the blowby gas can be reduced. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 is a right side view of a V-type internal combustion engine to which the present invention is applied; 
     FIG. 2 is a sectional view substantially taken along a line II—II of FIG.  1 . 
     FIG. 3 is a plane view of a cylinder block of FIG. 1; 
     FIG. 4 is a right side view of the cylinder block and a lower crankcase of FIG. 1; 
     FIG. 5 is a sectional view of the cylinder block and the lower crankcase taken along a line V—V of FIG. 3; 
     FIG. 6 is a sectional view taken along a line VI—VI of FIG. 5; 
     FIG. 7 is a sectional view taken along a line VII—VII of FIG. 4; 
     FIG. 8 is a front view of the lower crankcase viewed in the direction of an arrow VIII of FIG. 4; 
     FIG. 9 is a sectional view taken along a line IX—IX of FIG. 8; 
     FIG. 10 is a sectional view taken along a line X—X of FIG. 4; 
     FIG. 11 is a bottom view of the cylinder block; 
     FIG. 12 is a view taken along a line XII—XII of FIG. 3; 
     FIG. 13 is an end face view of a rear bank of the cylinder block in a direction XIII of FIG. 12; and 
     FIG. 14 is a bottom view of a rear cylinder head. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An explanation will now be provided for embodiments of the present invention with reference to the accompanying drawings. 
     Referring to FIGS. 1 through 5, a V-type internal combustion engine E to which the present invention is applied, is a V-type 5-cylinder 4-cycle internal combustion engine of a dual overhead cam (DOHC) type. The engine is also a water-cooled type, and which constitutes a power apparatus mounted to a motorcycle along with a transmission apparatus for transmitting power to rear wheels. As illustrated in FIG. 1, the internal combustion engine E is provided with, in a front and rear direction, a cylinder block  1  having a front bank  4 F and a rear bank  4 R forming a V-bank in a V-like shape having an angle of substantially 75°. A front cylinder head  2 F and a rear cylinder head  2 R are fastened to upper end faces  4 F a  and  4 R a  of the cylinder block  1  at the respective banks  4 F and  4 R. A front head cover  3 F and a rear head cover  3 R are respectively fastened to the two cylinder heads  2 F and  2 R. Furthermore, a lower portion of the cylinder block  1  is formed with an upper crankcase  5  and an upper portion thereof is formed with the two banks  4 F and  4 R, respectively. Furthermore, a lower end face  5   a  of the upper crankcase  5  is matched with an upper end face  6   a  of a lower crankcase  6  to thereby fasten the cylinder block  1  and the lower crankcase  6 . Furthermore, a crankshaft  7  is transversely arranged in a left and right direction of a vehicle body, and is rotatably supported by the crankcase constituted by the upper crankcase  5  and the lower crankcase  6  in a state in which a rotational axis line L thereof is disposed on a match face of the lower end face  5   a  of the upper crankcase  5  and the upper end face  6   a  of the lower crankcase  6 . Furthermore, in the specification, the terms “front, rear, left, right” signify “front, rear, left, right” with respect to the vehicle body. 
     Furthermore, with reference to FIG. 5, a front portion of the upper crankcase  5  and a front portion of the lower crankcase  6  forms the crankcase  8  containing the crankshaft  7 . Furthermore, a rear portion of the upper crankcase  5  and a rear portion of the lower crankcase  6  forms a transmission chamber  9  containing a wet type multi-plate friction clutch (not illustrated) and a gear transmission M of an always in-mesh type constituting a transmission apparatus. The lower end face  6   b  of the lower crankcase  6  is matched with an upper end face  10   a  of an oil pan  10  in oil tight relationship to thereby fasten the oil pan  10 . 
     Furthermore, the crankcase  8  and the transmission chamber  9  are separated by a bearing portion D 1  constituting a left side wall and a bearing portion D 4  constituting a right side wall (refer to FIG. 2) constituting two side walls of the cylinder block  1  and the lower crankcase  6 . The crankcase  8  and the transmission chamber  9  are separated by a partition wall comprising an upper partition wall A 1  formed at the cylinder block  1  and a lower partition wall A 2  formed at the lower crankcase  6  to thereby constitute chambers independent from each other. Accordingly, the crankcase  8  is hermetically closed. 
     Also with reference to FIG. 2, the front bank  4 F is provided with three cylinders C 1 , C 3  and C 5  aligned and integrally coupled in the direction of the rotational axis line L of the crankshaft  7 . Furthermore, center lines N 1 , N 3  and N 5  of the cylinder bores B 1 , B 3  and B 5  formed at the respective cylinders C 1 , C 3  and C 5 , are directed from the rotational axis line L in skewed front upper directions and the respective cylinders C 1 , C 3  and C 5  are inclined forwardly. Furthermore, the rear bank  4 R is provided with two cylinders C 2  and C 4  aligned and integrally coupled along the direction of the rotational axis line L. Center lines N 2  and N 4  of cylinder bores B 2  and B 4  formed at the respective cylinders C 2  and C 4  are directed from the rotational axis line L in skewed rear upper directions and the respective cylinders C 2  and C 4  are inclined rearwardly. Pistons P 1  through P 5  are slidably fitted in the cylinder bores B 1  through B 5  of the respective cylinders C 1  through C 5 . The pistons P 1  through P 5  are reciprocated by combustion pressure from combustion chambers formed between the respective pistons P 1  through P 5  and the cylinder heads  2 F and  2 R. The pistons P 1  through P 5  rotate the crankshaft  7  via connecting rods R 1  through R 5  connecting the respective pistons P 1  through P 5  and the crankshaft  7 . 
     Specifically, the crankshaft  7  is supported by the cylinder block  1  and the lower crankcase  6  by four bearing portions D 1  through D 4  respectively formed in the direction of the rotational axis line L at predetermined intervals at journals J 1  through J 4  via main bearings  11 . Furthermore, the crankcase  8  is partitioned into three chambers in the direction of the rotational axis line L with the two bearing portions D 1  and D 4  being located at the ends and the two bearing portions D 2  and D 3  being disposed in the middle. 
     In the crankshaft  7 , a crankpin K 1  between the bearing portion D 1  and the bearing portion D 2 , is connected with both of the connecting rods R 1  and R 2  connected to piston pins S 1  and S 2  of the two pistons P 1  and P 2 . A crankpin K 2  disposed between the bearing portion D 2  and the bearing portion D 3  and contiguous with the crankpin K 1 , is connected only with the connecting rod R 3  connected to a piston pin S 3  of the piston P 3 . Furthermore, a crankpin K 3  disposed between the bearing portion D 3  and the bearing portion D 4  and contiguous with the crankpin K 2 , is connected with both of the connecting rods R 4  and R 5  connected to a fourth and a fifth piston pin S 4  and S 5  of the two pistons P 4  and P 5 . 
     Referring to FIG. 1, the respective cylinder heads  2 F and  2 R are formed with an intake port  12  having a pair of inlet ports opened toward the combustion chamber and an exhaust port  13  having a pair of outlet ports. The intake ports  12  and the exhaust ports  13  are provided with a pair of intake valves  14  respectively opening and closing the pair of inlet ports and a pair of exhaust valves  15  for opening and closing the pair of outlet ports. In addition, each of the cylinder heads  2 F and  2 R are provided with an ignition plug T facing inside of the respective combustion chamber, at the respective combustion chamber. Furthermore, in the front cylinder head  2 F, an intake cam shaft  16  and an exhaust cam shaft  17  are rotatably supported by four cam holders arranged at intervals in the direction of the rotational axis line L. In the rear cylinder head  2 R, the intake cam shaft  16  and the exhaust cam shaft  17  are rotatably supported by three cam holders arranged at intervals in the direction of the rotational axis line L. Furthermore, two sets of the two cam shafts  16  and  17  are respectively driven to rotate at a rotational number of ½ of that of the crankshaft  7  by power of the crankshaft  7  transmitted from an intermediate gear  19  in mesh with the drive gear  18  provided at a right end portion of the crankshaft  7  via a front side timing gear train  20  and a rear side timing gear train  21 . The cam shafts  16  and  17  drive the respective intake valves  14  and the respective exhaust valves  15  at predetermined timings. 
     Furthermore, an intake apparatus connected to the respective intake ports  12 , is arranged on the inner side of the V-bank. An exhaust pipe connected to the exhaust ports  13  of the cylinders C 1 , C 3  and C 5  of the front bank  4 F, is extended in the rear direction by passing through a recess formed at the right side of the lower portion of the left wall of the oil pan  10 . 
     Furthermore, as illustrated in FIG. 2, the drive gear  18  and the intermediate gears  19  disposed on the right side of the cylinder block  1  and the two cylinder heads  2 F and  2 R, are covered by a cover  22  attached to right side walls of the upper crankcase  5  and the lower crankcase  6 . Two timing gear trains  20  and  21  are arranged in a cavity Y formed at right end portions of the two banks  4 F and  4 R of the cylinder block  1  and the two cylinder heads  2 F and  2 R. Therefore, the drive gear  18 , the intermediate gears  19  and the two timing gear trains  20  and  21  are contained in a gear chamber  23  constituted by a space formed by the right side walls and the cover  22  and the cavity Y. The gear chamber  23  is in communication with the oil pan  10  via a cavity formed at the lower crankcase  6  formed therebelow (not illustrated). Furthermore, an alternator  24  is provided at a left end portion of the crankshaft  7 . 
     Referring to FIG. 1, the power of the crankshaft  7  is transmitted to the multi-plate friction clutch via a primary speed reducing mechanism comprising a primary drive gear  25  and a primary driven gear  26  and is transmitted further to the gear transmission M. A main shaft  27  and a counter shaft  28  of the gear transmission M are respectively provided with a main gear group and a counter gear group, not illustrated. When a shift drum  29  is rotated by a speed change operating mechanism, shift forks engaged with cam grooves of the shift drum  29  are moved in the left and right direction on a support shaft  30 . Gears of the main gear group and the gears of the counter gear group in correspondence with the speed change operation are brought in mesh with each other. The power of the crankshaft  7  is subjected to speed change and is transmitted from the main shaft  27  to the counter shaft  28  and power of the counter shaft  28  is transmitted to rear wheels via a secondary speed reducing mechanism having a chain (not illustrated). 
     Furthermore, the power of the crankshaft  7  is transmitted to a pump gear  32  provided at a drive shaft  33  of an oil pump unit U via an intermediate gear  31   b  in mesh with a pump drive gear  31   a  rotated integrally with the primary driven gear  26  rotatably supported by the main shaft  27  to drive the oil pump unit U. The left end of the drive shaft  33  is coupled with a rotating shaft provided with an impeller of a cooling water pump, not illustrated. 
     An explanation will now be given of a lubricating system for the power apparatus. An oil strainer  34  is arranged in the oil pan  10 . An oil pipe  35  extends from the oil strainer  34  in the upper direction and is connected to a fourth intake port of a feed pump  36  of the oil pump unit U. Referring to FIGS. 5 and 6, the oil pump unit U is provided with a first scavenge pump  37 , the feed pump  36 , a second scavenge pump  38  and a third scavenge pump  39  in the axial direction of the drive shaft  33  successively from the right. The pumps  36  through  39  are constituted by trochoid pumps. The oil pump unit U is provided with a first intake port  37   a  of the first scavenge pump  37 , a second intake port  38   a  of the second scavenge pump  38 , a third intake port  39   a  of the third scavenge pump  39  and a single first delivery port  40  communicating with the respective delivery ports (not illustrated) of the first through the third scavenge pumps  37  through  39 . Furthermore, the oil pump unit U is provided with a fourth input port  36   a  of the feed pump  36  and a relief port  36   b  provided with a relief valve and a second delivery port  36   c . The first delivery port  40  is provided in the vicinity of the second scavenge pump  38  in the axial direction of the drive shaft  33  and is directed substantially toward the main shaft  27  of the gear transmission M. 
     Referring to FIG. 5, the lower crankcase  6  is provided with an inclined partition wall A 2   a  extending from a front portion of a lower end face  6   b  coupled with the oil pan  10  in a skewed rear upper direction and constituting an acute angle between the inclined partition wall A 2   a  and a flat wall portion  6   c   2 , described below, of a front wall  6   c  of the lower crankcase  6 . The oil pump unit U is attached to an attaching face formed on the side of the oil pan  10  of the inclined partition wall A 2   a  constituting a portion of the lower partition wall A 2 . In a state in which the oil pump unit U is attached to the attaching face, as illustrated in FIG. 7, the inclined partition wall A 2   a  is provided with a first, a second and a third intake port  41 ,  42  and  43 , respectively connected to the first, the second and the third input ports  37   a ,  38   a  and  39   a . Furthermore, lubricating oil which is supplied into the crankcase  8 , once lubricating necessary lubricating portions and flowing down to the bottom portion of the crankcase  8 , is sucked respectively from the first through the third intake ports  41  through  43  to the first through the third scavenge pumps  37  through  39  and is discharged from the first delivery port  40  into the transmission chamber  9 . 
     Furthermore, as illustrated in FIGS. 8 and 9, in the inclined partition wall A 2   a , at a position slightly upward from the lower end face  6   b , there an oil path G 1  is provided to the second delivery port  36   c  by coupling with an end face of the second delivery port  36   c . The oil path G 1  is connected to an oil path G 2  constituting an introducing oil path G 4 , described below, for conducting the lubricating oil to an oil filter  44  for cleaning the lubricating oil by removing foreign matters in the lubricating oil by a filter element  44   a . Referring to FIGS. 5 and 8, a cylindrical shaped oil filter  44  is attached to an attaching seat  45  formed at the front wall  6   c  of the lower crankcase  6 . Specifically, the front wall  6   c  is provided with a partially cylindrical curved wall portion  6   c   1  constituting a portion in a peripheral direction of a substantially cylindrical peripheral wall with the rotational axis line L as a center line. The flat wall portion  6   c   2  substantially in a flat plate shape continuous with a lower end portion  6   c   1   a  of the curved wall portion  6   c   1  is disposed substantially right below the rotational axis line L and extends in a vertical lower direction to reach a lower end face  6   b . A portion of the lower end face  6   b  in correspondence with the flat wall portion  6   c   2  is matched to the upper end face  11   a  at the front wall  10   b  portion in the flat plate shape of the oil pan  10 . 
     The attaching seat  45  projects from front faces of the curved wall portion  6   c   1  and the flat wall portion  6   c   2  in a space formed by the curved wall portion  6   c   1  and the flat wall portion  6   c   2 . An attaching face  45   a  attached with the oil filter  44 , is disposed upward from the lower end face  6   b , disposed rearward from a contact portion  6   c   3  of the front face in contact with an assumed plane H in contact with a frontmost portion of the lower end face  6   b  and a front face of the curved wall portion  6   c   1 . Furthermore, the attaching face  45   a  is formed at a position slightly projected forward from the assumed plane H and substantially along the assumed plane H. Also with reference to FIG. 10, inside of the attaching seat  45  an oil path G 3  is formed comprising a groove in a ring-like shape opened to the attaching face  45   a  and the oil path G 2  one end of which is connected to the oil path G 1  and other end of which is connected to a lower portion of the oil path G 3  from a tangential direction of the oil path G 3 . An introducing oil path G 4  is constituted by the oil path G 2  and the oil path G 3 . The lubricating oil delivered from the feed pump  36  flows into the oil filter  44  via the introducing oil path G 4 . 
     Furthermore, at a central portion of a circular ring of the oil path G 3 , a screw hole  46  is formed with female threads in a direction orthogonal to the attaching face  45   a . The screw hole  46  is threaded with a cylindrical shaped threaded portion  44   b  for forming an oil path to an inside of the oil filter  44 . Furthermore, an introducing oil path G 5  is formed opened to a peripheral wall in the vicinity of a bottom portion of the screw hole  46  and extends substantially in parallel with the rotational axis line L and accordingly, the lower end portion  6   c   1   a  of the curved wall portion  6   c   1  and to the right side of the screw hole  46  in the vicinity of the lower end portion  6   c   1   a.    
     With reference to FIGS. 4 and 10, the introducing oil path G 5  is connected to an oil path G 6  formed at the front wall  6   c  and opened to the upper end face  6   a  at the right end portion of the lower crankcase  6 . The oil path G 6  is connected to one end of an oil path G 7  formed at the right end portion of the cylinder block  1 . The other end of the oil path G 7  is connected to a main gallery G 8  formed at a bottom wall portion  1   a  of the V-bank of the cylinder block  1  at the upper end face  6   a . The main gallery G 8  extends from a right end portion of the bottom wall portion  1   a  substantially in parallel with the rotational axis line L, opens at a left end face of the cylinder block  1  (refer to FIG.  3 ), as illustrated in FIG. 2, and is connected to an oil path G 9  formed at an alternator cover  37  fastened to a left end face of the crankshaft  7 . The oil path G 9  is connected to an oil path G 11  formed by utilizing a screw hole threaded with a bolt  48  of the crankshaft  7  via an oil path G 10  formed at an inside of the bolt  48  for fixing a rotor of the alternator  24  to the crankshaft  7 . Furthermore, the oil path G 11  is connected with one end of an in-shaft oil path G 12  formed at an inside of the crankshaft  7 . The other end of the in-shaft oil path G 12  is connected to an oil path G 13  formed by utilizing a screw hole threaded with a bolt  49  for fixing a ring for hampering movement of the drive gear  18  in the direction of the rotational axis line L at the right end portion of the crankshaft  7 . The oil path G 13  is connected to an oil path G 16  provided at the cover  22  via an oil path G 14  formed at inside of the bolt  49 . An oil path G 15  is formed at a cap  50  mounted to the cover  22 . The lubricating oil which has passed through the oil path G 16  is injected from a nozzle  51  provided at the other end of the oil path G 16  toward the intermediate gears  19 , the drive gear  18  and the two timing gear trains  20  and  21 . 
     Furthermore, the first through the third crankpins K 1  through K 3  are formed, in the diameter direction, with oil paths G 17  connected to the in-shaft oil path G 12  for supplying the lubricating oil to the connecting portions of the respective crankpins K 1  through K 3  connected with the connecting rods R 1  through R 5 . The journals J 2  and J 3  are formed, in the diameter direction, with oil paths G 18  connected to the in-shaft oil path G 12  for supplying the lubricating oil to the bearing portions D 2  and D 3 . Furthermore, the journals J 1  and J 4  are formed, in the diameter direction, with oil paths G 19  respectively connected to the oil path G 11  and the oil path G 13  for supplying the lubricating oil to the two bearing portions D 1  and D 4 . 
     Furthermore, referring to FIGS. 3 and 4, in the main gallery G 8 , at a portion thereof connected with the oil path G 7 , head oil paths G 20  and G 21  are formed extending from the connected portion to the cylinder heads  2 F and  2 R of the respective banks  4 R and  4 F in the cylinder block  1 , by way of the respective head oil paths G 20  and G 21 . The lubricating oil is supplied to a front valve operating apparatus VF constituted by the two cam shafts  16  and  17 . Lifters and the like are arranged at an inside of a front valve operating chamber  52 F formed by the front cylinder head  2 F and the front head cover  3 F. A rear valve operating chamber VR is constituted by the two cam shafts  16  and  17 . Lifters and the like are arranged at an inside of a rear valve operating chamber  52 R formed by the rear cylinder head  2 R and the rear head cover  3 R (refer to FIG.  1 ). That is, the respective head oil paths G 20  and G 21  are connected to oil paths formed at cam holders fixed to the respective cylinder heads  2 F and  2 R and disposed at right ends thereof at upper end faces  4 F a  and  4 R a . The respective valve operating apparatus VF and FR are lubricated by lubricating oil supplied from the cam holders to hollow portions of the two cam shafts  16  and  17  and supplied from oil holes provided at necessary portions of the two cam shafts  16  and  17 . 
     Furthermore, referring to FIGS. 4 and 11, at the main gallery G 8 , contiguous with the right side of the cylinder C 2  of the rear bank  4 R, an oil path G 22  is formed opened to the lower end face  5   a  of the cylinder block  1  (lower crankcase  5 ). The oil path G 22  branches, by way of an oil path  23  comprising a groove formed at the lower end face  5   a  of the cylinder block  1  and an oil path G 24  comprising a groove formed at the upper end face  6   a  of the lower crankcase  6   a , to pass an oil path G 25  and an oil path G 26  formed at the lower crankcase  6 . The lubricating oil is supplied to the sliding portions of the main shaft  27  and the support shaft  30  of the gear transmission M. 
     Furthermore, referring to FIGS. 5 and 11, along the main gallery G 8 , at an inner face of the bottom wall portion  1   a  of the cylinder block  1 , five mounting portions  53  are provided mounted with nozzles  54  (refer to FIG. 5) in correspondence with the respective cylinder bores B 1  through B 5  at portions including the center lines N 1  through N 5  of the respective cylinder bores B 1  through B 5  and intersected with assumed planes orthogonal to the rotational axis line L. By injecting the lubricating oil which has passed through oil paths G 27  provided at the respective mounting portions  53  and connected to the main gallery G 8  from the nozzles  54 , the lubricating oil is supplied to the connecting portions of the respective pistons S 1  through S 5  and the respective connecting rods R 1  through R 5  and sliding portions of the respective cylinders C 1  through C 5  and the respective pistons P 1  through P 5 . 
     An explanation will now be given of a return oil path of the lubricating oil and a breather apparatus. 
     First, with regard to the front bank  4 F, referring to FIGS. 3 and 11, at the front wall of the cylinder head  2 F, at a left side portion of the cylinder C 1 , that is, the left end portion of the front bank  4 F, between the two cylinders C 1  and C 3  and between the two cylinders C 3  and C 5 , a first, a second and a third return oil path  55 ,  56  and  57  of the lubricating oil are formed, respectively having opening portions  55   a ,  56   a  and  57   a  at the upper end face  4 F a  of the cylinder block  1 . Furthermore, oil paths connected to the respective opening portions  55   a ,  56   a  and  57   a  are formed to open to an inside of the front valve operating chamber  52 F. The lubricating oil which has finished lubricating the front valve operating apparatus VF is gathered at the lower portion of the cylinder block  1  by way of the first through the third return oil paths  55  through  57  formed at the front wall of the cylinder block  1 , passes through a return oil pipe  58  (refer to FIG. 1) connected thereto at the lower end face  5   a  of the cylinder block  1  and returns to the oil pan  10  by way of an oil path  59  (refer to FIG. 7) having an opening portion  59   a  (refer to FIG. 8) provided below the flat wall portion  6   c   2  of the front wall  6   c  of the lower crankcase  6 . 
     In addition, referring to FIGS. 12 and 13, in the rear bank  4 R, substantially in the front and rear direction, that is, in a direction orthogonal to an assumed plane including the rotational axis line L and dividing the V-bank in two, at a position opposed to the cylinder bore B 3  of the front bank  4 F, between the cylinder bore B 2  and the cylinder bore B 4  in the direction of the rotational axis line L, a space portion  60  is formed having a width in the direction of the rotational axis line L to a degree slightly smaller than the diameter of the cylinder bore B 3  and substantially equal to an interval in the direction of the rotational axis line L between a central point of the journal J 2  and a central point of the journal J 3  in the direction of the rotational axis line L. As a result, as illustrated in FIG. 3, the space portions  60  is within a range such that it does not project relative to the front bank  4 F in the direction of the rotational axis line L. 
     In the space portion  60 , a cavity  62  is formed having a partition wall  61  extending substantially in parallel with the direction of the rotational axis line L and continuous with an outer peripheral wall C 2   a  of the cylinder C 2  and an outer peripheral wall C 4   a  of the cylinder C 4 . The cavity  62  is formed between an inclined partition wall A 1   a  constituting a portion of the upper partition wall A 1 , extending from the bottom wall portion  1   a  in a skewed rear lower direction and reaching a rear end of a lower portion of the rear bank  4 R and an upper end face  4 R a  of the rear bank  4 R, between the outer peripheral wall C 2   a  of the cylinder C 2  and the outer peripheral wall C 4   a  of the cylinder C 4  and between the inner side wall  4 R b  of the V-bank of the rear bank  4 R and an outer side wall  4 R c  of the V-bank extending in a skewed rear lower direction and continuous to an upper wall  5 C of the transmission chamber  9 . Furthermore, between a vertical partition wall A 1   b  extending from an end portion of the inclined partition wall A 1   a  on the side of the transmission chamber  9  in the vertical lower direction toward the lower end face  5   a  and constituting the upper partition wall A 1  and the outer side wall  4 R c  of the V-bank, an opening portion  63  is formed for communicating the cavity  62  and the transmission chamber  9 . Furthermore, a width of the cavity  62  in the direction of the rotational axis line L is substantially equal to an interval between the bearing portion D 2  and the bearing portion D 3  in the rotating shaft direction. A width thereof in a direction orthogonal to an assumed plane including the rotational axis line L and the center line N 2  or the center line N 4  (hereinafter, referred to as “orthogonal” direction) is substantially equal to a width of the rear bank  4 R in the orthogonal direction at portions of the cylinders C 2  and C 4 . 
     Above the cavity  62 , a path  64  is formed interposing the partition wall  61 , extending to substantially a central portion of the upper end face  4 R a  and the inclined partition wall A 1   a  in a direction of the center line N 2  or the center line N 4 . The path  64  has an opening portion  64   a  at the upper end face  4 R a  on an inner side of the V-bank. A path  65  is formed having an opening portion  65   a  at the upper end face  4 R a  and constituting the opening portion  63  at its rear portion on an outer side of the V-bank. The paths  64  and  65  are arranged in parallel with the direction of the rotational axis line L by the partition wall  61 . Furthermore, by a path  66  formed below the partition wall  61  and below the cavity  62 , the path  64  and the opening portion  63  are in communication with each other. Furthermore, a breather path  67  of the cylinder block  1  is constituted by the opening portion  63 , the path  66  and the path  64 . A oil return path  68  of the lubricating oil from the rear valve operating chamber  52 R in the cylinder  1  is constituted by the path  65  and the opening portion  63 . 
     Furthermore, at an inside of the partition wall  61 , a water path  61   a  is provided for communicating a cooling water jacket of the cylinder C 2  and a cooling water jacket of the cylinder C 4 . Furthermore, further, at an upper portion of the partition wall  61 , an eaves portion  61   b  is formed extending to the outer side of the V-bank and a projected edge portion  61   c  is formed constituting a front end portion of the eaves portion  61   b  and produced by projecting an edge portion of the opening portion  65   a  of the path  65  on the side of the partition wall  61  over the direction of the rotational axis line L in the lower direction. Furthermore, the opening portion  63  constituting a flow inlet of the breather path  67  and constituting a flow outlet of the return oil path  68 , is provided below the partition wall  61  and to a side more proximate to the outer side wall  4 R c  of the V-bank than a side face  61   d  on the side of the return oil path  68  of the partition wall  61  and is disposed at a position at which a portion of the blowby gas flowing from the opening portion  63  impinges on the side face  61   d  and a flow elevating along the side face  61   d  is produced. 
     Furthermore, in the rear cylinder head  2 R, as illustrated in FIGS. 12 and 14, a space portion  70  is formed at a position in correspondence with the space portion  60 . A breather path  71  and a return oil path  72  of the lubricating oil are formed having opening portions  71   a  and  72   a  having sizes respectively matching precisely with the opening portions  64   a  and  65   a  of the path  64  and the path  65  and communicating with inside of the rear valve operating chamber  52 R. Furthermore, a partition wall  73  is formed having a lower end face matched with an upper end face of the partition wall  61 . At inside of the partition wall  73 , a water path  73   a  is formed for communicating a cooling water jacket formed by surrounding the combustion chamber of the cylinder C 2  at the rear cylinder head  2 R, the ignition plug T and a lower portion of a cylindrical portion  69  (refer to FIG. 2) containing an ignition coil and a cooling water jacket formed by surrounding the combustion chamber of the cylinder C 4 . The ignition plug T and a lower portion of a pipe contain an ignition coil. 
     Furthermore, as illustrated in FIGS. 2 and 12, at an upper portion of the rear head cover  3 R, above the breather paths  67  and  71 , a breather chamber  74  is provided having an inlet  74   a  opened to an inside of the rear valve operating chamber  52 R. A recirculating pipe (not illustrated) connected to a connection pipe  75  connected to the breather chamber  74  is connected to an intake path constituting an intake system of the internal combustion engine E. 
     Thereby, blowby gas in the crankcase  8  sucked by the first through the third scavenge pumps  37  through  39  along with the lubricating oil and discharged into the transmission chamber  9 , flows from the transmission chamber  9  into the breather chamber  74  by passing through the breather paths  67  and  71 , is recirculated from the breather chamber  74  to the intake path via the recirculating pipe and is supplied to the combustion chamber. Therefore, a breather apparatus is formed for recirculating the blowby gas from the crankcase  8  to the intake path by the first through the third intake ports  41  through  43 , the first through the third scavenge pumps  37  through  39 , the transmission chamber  9 , the breather paths  67  and  71 , the rear valve operating chamber  52 R, the breather chamber  74 , the connection tube  75  and the recirculating pipe. 
     An explanation will now be given of the operation and effect of the embodiment constituted as described above. 
     When the internal combustion engine E is operated and the oil pump unit U is operated, the lubricating oil sucked from the oil pan  10  to the feed pump  36  by passing through the oil strainer  34 , is delivered from the second delivery port  36   c , flows into the oil filter  44  by way of the oil path G 1  and the introducing oil path G 4 , is removed of foreign matters or the like by the oil filter  44  and is supplied to the main gallery G 8  by passing through the introducing oil path G 5 , the oil path G 6  and the oil path G 7 . 
     The lubricating oil flowing from the main gallery G 8  into the in-shaft oil path G 12  via the oil paths G 9 , G 10  and G 11 , is supplied to the journals J 1  through J 4  and the crankpins K 1  through K 3 , lubricates the respective sliding portions, and is injected from the nozzles  51 , lubricates the mesh portion and the sliding portions of the drive gear  18 , the intermediate gears  19  and the two timing gear trains  20  and  21 . Furthermore, the lubricating oil is injected from the nozzles  54  and lubricates the sliding portions of the respective piston pins S 1  through S 5  and the sliding portions of the respective pistons P 1  through P 5  and the respective cylinders C 1  through C 5 . In addition, the lubricating oil flowing from the main gallery G 8  into the head oil paths G 20  and G 21 , lubricates the sliding portions of the valve operating apparatus VF and VR in the respective valve operating chambers  52 F and  52 R. 
     Furthermore, the lubricating oil which has been supplied to the crankcase  8  and has finished lubricating the lubricating portions of the sliding portions and the like described above, flows down to the bottom portion of the crankcase  8  formed between the front wall  6   c  and the inclined partition wall A 2   a , and is sucked from the first through the third intake ports  41  through  43  to the first through the third scavenge pumps  37  through  39 . The lubricating oil delivered from the scavenge pumps  37  through  39 , is discharged from the first delivery port  40  into the transmission chamber  9 , lubricates the lubricating portions of the sliding portions of the multi-plate friction clutch, the gear transmission M and the like and thereafter returns to the oil pan  10 . In addition, the oil which has lubricated the drive gear  18 , the intermediate gears  19  and the two timing gear trains  20  and  21 , returns from the lower portion of the gear chamber  23  opened to the oil pan  10  to the oil pan  10 . The lubricating oil supplied to the front valve operating chamber  52 F, returns to the oil pan  10  via the return oil paths  55  through  57  and the return pipe  58 . The lubricating oil supplied to the rear valve operating chamber  52 R returns to the oil pan  10  via the return oil paths  72  and  68  and via the transmission chamber  9 . In this way, the lubricating oil supplied into the crankcase  8  is sucked by the first through the third scavenge pumps  37  through  39 . Therefore, power loss is not caused by scraping up the lubricating oil by the crankshaft  7 . 
     Furthermore, as described above, blowby gas in the crankcase  8  is sucked to the first through third scavenge pumps  37  through  39  along with the lubricating oil, is discharged into the transmission chamber  9 , is recirculated from the transmission chamber  9  to the intake path by way of the breather path  67  formed at the space portion  60 , the breather path  71  formed at the space portion  70 , the rear valve operating chamber  52 R, the breather chamber  74  and the recirculating pipe, is supplied to the combustion chamber and is combusted. 
     In the rear bank  4 R, the space portion  60  formed between the cylinder bore B 2  and the cylinder bore B 4  at the position opposed to the cylinder bore B 3  of the front bank  4 F, is provided with a minimum width in the direction of the rotational axis line L to a degree slightly smaller than the diameter of the cylinder bore B 3  within a range such that it does not project in the direction of the rotational axis line L relative to the front bank  4 F. Therefore, the breather path  67  is provided a sufficiently large flow path area without increasing the width in the direction of the rotational axis line L of the rear bank  4 R having a number of cylinders smaller than that of the front bank  4 F, and the width in the orthogonal direction. Accordingly, the width in the direction of the rotational axis line L of the cylinder block  1  is not increased, the advantage of the cylinder block  1  being downsized by reducing the width in the direction of the rotational axis line L by coupling the two connecting rods R 1  and R 2  and the two connecting rods R 4  and R 5  respectively to the two crankpins K 1  and K 3  is not deteriorated, and the weight of the cylinder block  1  is reduced. Furthermore, by increasing the flow path area of the breather path  67 , a flow rate of the blowby gas flowing in the breather path  67  is kept to a minimum and therefore, an effect of separating lubricating oil mist mixed in the blowby gas is expedited. 
     The space portion  60  is provided with a width in the direction of the rotational axis line L to a degree slightly smaller than the diameter of the cylinder bore B 3  within a range which does not project to the front bank  4 F in the direction of the rotational axis line L. Therefore, the return oil path  68  of the lubricating oil having a sufficiently large flow path area can be formed in addition to the breather path  67  having a sufficient flow path area without enlarging the cylinder block  1 . Furthermore, lubricating oil from the rear valve operating chamber  52 R returns smoothly, the blowby gas and the lubricating oil can be restrained from being mixed with each other by the partition wall  61  partitioning the two paths  64  and  65  in parallel with the direction of the rotational axis line L and an amount of the lubricating oil mist mixed into the blowby gas can be reduced. 
     By separating the crankcase  8  and the transmission chamber  9  by the partition wall comprising the upper partition wall A 1  and the lower partition wall A 2 , the breather path  67  constituted by the opening portion  63 , the path  66  and the path  64  is also separated from the crankcase  8 . Therefore, the lubricating oil scattered by rotating the crankshaft  7  does not directly intrude the breather path  67  and the lubricating oil mist is prevented from mixing with the blowby gas. 
     The partition wall  61  and the partition wall  73  are respectively formed with the water paths  61   a  and  73   a  of cooling water. Therefore, when warming up the internal combustion engine E, the breather paths  67  and  71  are warmed by cooling water from the cooling water jackets of the cylinder block  1  and the rear cylinder head  2 R as well as cooling water flowing in the water paths  61   a  and  73   a  of the partition walls  61  and  73 . Therefore, condensation of steam at the breather paths  67  and  71  and the breather chamber  74  is prevented and accordingly, water is prevented from mixing wtih the separated lubricating oil and a deterioration of the lubricating oil caused by mixing water can be avoided. 
     Furthermore, at the upper portion of the partition wall  61 , the eaves portion  61   b  extends to the outer side of the V-bank and the projected edge portion  61   c  constitutes the front end portion of the eaves portion  61   b . Therefore, although a portion of the blowby gas flowed from the opening portion  63  reaches the rear valve operating chamber  52 R by passing through the return oil paths  68  and  72 , a portion thereof impinges on the side face  61   d  of the partition wall  61  on the side of the return oil path  68  and an elevating flow is produced along the side face  61   d . Furthermore, the elevating blowby gas impinges on the lower face of the eaves portion  61   b  and the elevating flow is hampered and deflected to the lower side by the projected edge portion  61   c . Therefore, the flow of the lubricating oil passing through the return oil path  68  is significantly restrained from being hampered by the elevating blowby gas and the lubricating oil flows down to the return oil path  68  smoothly. 
     Furthermore, the attaching face  45   a  of the attaching seat  45  formed at the front wall  6   c  of the lower crankcase  6 , is disposed above the lower end face  6   b  coupled with the oil pan  10  of the lower crankcase  6  and is disposed at a position comparatively higher than that in the case of attaching the oil filter  44  to the oil pan  10  or the case of arranging the oil filter  44  to ride over the lower crankcase  6  and the oil pan  10 . Furthermore, the oil filter  44  is formed forward from the assumed plane H and substantially along the assumed plane H and therefore, regardless of presence of the curved wall portion  6   c   1  being bulged forwardly, the attaching face  45   a  can easily be recognized from above. Therefore, attachment and detachment of the oil filter  44  while confirming the attaching face  45   a  are facilitated and the operability of maintenance of the oil filter  44  is promoted. Furthermore, by disposing the attaching face  45   a  rearward from the contact portion  6   c   3  in contact with the assumed plane H on the front side of the curved wall portion  6   c   1  bulged to the front side of the front wall  6   c  of the lower crankcase  6 , an amount of projection of the oil filter  44  to the front side is restrained. Therefore, the internal combustion engine E can be downsized and there is increased a degree of freedom of arranging an exhaust pipe connected to the exhaust port  13 , extended to the lower side by passing through the front side of the front bank  4 F, bent to the left side at the lower side and extended through the space formed to recess the lower portion of the left wall of the oil pan  10  to the right side in the lower direction. 
     Furthermore, the attaching seat  45  is provided by utilizing the space formed between the front face of the curved wall portion  6   c   1  and the front face of the flat wall portion  6   c   2 . Furthermore, the introducing oil path G 4  and the introducing oil path G 5  are formed at an inside thereof. Therefore, it is not necessary to project the front wall  6   c  of the lower crankcase  6  into the crankcase  8  for forming the oil paths G 4  and G 5 , the inner structure of the crankcase  8  can be simplified, the crankcase can be downsized and accordingly, the internal combustion engine E can be downsized. Furthermoremore, the introducing path G 5  formed at a position more remote in the direction orthogonal to the attaching face  45   a  from the attaching face  45   a  directed in the skewed lower direction than the introducing oil path G 4 , is formed at a vicinity of the lower end portion  6   c   1   a  constituting a comer portion formed by the curved wall portion  6   c   1  and the flat wall portion  6   c   2 . Therefore, the inside of the attaching seat  45  can effectively be utilized, an amount of projecting the attaching seat  45  to the front side is reduced and accordingly, an amount of projecting the oil filter  44  to the front side is reduced and the internal combustion engine E can further be downsized. 
     An explanation will now be given of a modified constitution with regard to an embodiment modifying a portion of the constitution of the above-described embodiment as follows. 
     Although according to the embodiment, the internal combustion engine E is provided with a hermetically closed crankcase  8 , the breather apparatus may communicate with the breather path  67  via a path communicating with the crankcase without hermetically closing the crankcase. In that case, air downstream from an air cleaner of the intake system is introduced into the front valve operating chamber communicating with the crankcase via the path. Furthermore, a PCV valve can be provided at the breather chamber or the output pipe. 
     Although according to the embodiment, the V-type internal combustion engine E is constituted by 5 cylinders, the internal combustion engine E may be a V-type internal combustion engine having an odd number of cylinders, for example, it may be an internal combustion engine of 3 cylinders or 7 cylinders. Furthermore, in the case of a 3-cylinder V-type internal combustion engine, the space portion of the cylinder block is formed at a position contiguous with a cylinder bore of a bank having an odd number of the cylinder comprising 1 cylinder and by a width in a rotational axis line direction which does not project in the rotational axis line direction of a crankshaft relative to a bank having an even number of cylinders comprising 2 cylinders constituting a bank having a larger number of cylinders. 
     Furthermore, although according to the above-described embodiment, the first and the third crankpins K 1  and K 3  are respectively connected with two of the connecting rods R 1  and R 2  and two of the connecting rods R 4  and R 5 , there may be constituted a V-type internal combustion engine of a style which connects a single connecting rod to a respective crankpin. Furthermore, there may be constituted a V-type internal combustion engine of a style in which crankpins connected with two connecting rods and crankpins connected with a single connecting rod are irregularly present in a rotational axis line direction of a crankshaft. 
     Furthermore, although the two space portions  60  and  70  are formed with the two paths  64  and  65  respectively divided by the two partition walls  61  and  73 , the breather path  71  and the return oil path  72 , there may be formed a single path having an opening portion of an area equal to or larger than an area combined with the areas of the opening portions  64   a  and  65   a  of the two paths  64  and  65  without providing the two partition walls  61  and  70  and the path may serve as the breather path and the return oil path. Furthermore, the breather path and the return oil path may be formed only by the partition wall  61  without providing the partition wall  73 . 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.