Patent Publication Number: US-11047272-B2

Title: Engine lubrication system, engine, and vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese application JP2016-225036 filed on Nov. 18, 2016, the content of which is hereby incorporated by reference into this application. 
     FIELD OF THE INVENTION 
     The present application relates to an engine lubrication system, an engine, and a vehicle. 
     BACKGROUND OF THE INVENTION 
     As a lubricating system for an engine, a dry sump system has been known. Unlike a wet sump system, the dry sump system does not require a relatively large oil pan for accumulating oil. Thus, the dry sump system has an advantage of enabling downsizing of an engine. 
     In Japanese Patent Application Laid-open No. 2009-203960, there is described a multi-cylinder engine having such a configuration that pumps, which are smaller in number than crank chambers, are arranged outside an engine, and, among oil collection passages respectively formed for the crank chambers, the predetermined number of the oil collection passages are joined together and connected to at least one of the pumps. With this configuration, the oil is smoothly collected. 
     SUMMARY OF THE INVENTION 
     However, when the pumps are arranged outside the engine as described in Japanese Patent Application Laid-open No. 2009-203960, it is necessary to firmly form the pumps to protect the pumps from a flying object such as a stone, and to further prevent leakage of oil. In particular, a vehicle for use in rough terrain, such as a recreational off-highway vehicle (ROV), has a higher need to protect the pumps from a flying object such as a stone than a general automobile. 
     The present application has been made to solve the above-mentioned problem, and one object is to provide an engine lubrication system, an engine, and a vehicle, capable of protecting a pump while increasing an oil collection efficiency. 
     According to one embodiment disclosed in the present application, there is provided an engine lubrication system including an oil passage allowing inflow of oil in a crank chamber partitioned off in a crankcase of an engine, at least a part of the oil passage being formed by the crankcase, a scavenge pump accommodated in the crankcase and sucking the oil from the oil passage, an oil tank accumulating the oil sucked by the scavenge pump, and a feed pump supplying, to the engine, the oil accumulated in the oil tank. 
     Further, according to one embodiment disclosed in the present application, there is provided an engine including a crankcase, an oil passage allowing inflow of oil in a crank chamber partitioned off in the crankcase, at least a part of the oil passage being formed by the crankcase, and a scavenge pump accommodated in the crankcase, and sucking the oil from the oil passage to supply the oil into an oil tank. 
     Further, according to one embodiment disclosed in the present application, there is provided a vehicle including an engine including an oil passage allowing inflow of oil in a crank chamber partitioned off in a crankcase, at least a part of the oil passage formed by the crankcase, a scavenge pump sucking the oil from the oil passage, an oil tank arranged outside the engine and accumulating the oil sucked by the scavenge pump, a feed pump supplying, to the engine, the oil accumulated in the oil tank, and a plurality of seats aligned in a right-and-left direction of the vehicle. At least a part of the engine is located between the plurality of seats in plan view, and is located below the plurality of seats in side view. 
     According to the above-mentioned embodiment, the oil is sucked from the oil passage that allows inflow of the oil in the crank chamber. Thus, the oil collecting efficiency can be increased. Further, the scavenge pump is accommodated in the crankcase. Thus, the pump can be protected. 
     When the scavenge pump is accommodated in the crankcase, the oil passage can be reduced in length as compared to a case in which the scavenge pump is arranged outside the engine. Thus, suction resistance can be reduced, and the oil collection efficiency can be increased. 
     Other objects and features of this invention will be in part apparent and in part point pointed out hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following drawings illustrate examples of various components of the invention disclosed herein, and are for illustrative purposes only. 
         FIG. 1  is a left side view for illustrating a vehicle according to an embodiment of the vehicle. 
         FIG. 2  is a back view for illustrating front row seats and a periphery thereof. 
         FIG. 3  is a left side view for illustrating an embodiment of an engine unit. 
         FIG. 4  is a developed sectional view for illustrating the engine unit. 
         FIG. 5  is a top view for illustrating an embodiment of a lower crankcase. 
         FIG. 6  is a left side view for illustrating the lower crankcase. 
         FIG. 7  is a right side view for illustrating the loner crankcase. 
         FIG. 8  is a bottom view for illustrating the lower crankcase. 
         FIG. 9  is a bottom view for illustrating the lower crankcase to which an oil pan is mounted. 
         FIG. 10  is an enlarged bottom view for illustrating a region of the oil pan, which is covered with a cover. 
         FIG. 11  is a sectional view for illustrating the lower crankcase to which the oil pan is mounted. 
         FIG. 12  is a sectional view for illustrating an embodiment of a pump unit. 
         FIG. 13  is an enlarged sectional view for illustrating an embodiment of a main part of an engine. 
         FIG. 14  is a schematic view for illustrating an embodiment of an oil-lubricated path for the engine. 
         FIG. 15  is an enlarged schematic view for illustrating an embodiment of an oil collecting region in the oil-lubricated path. 
         FIG. 16  is a schematic view for illustrating a modified example of the oil collecting region. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the present invention may be embodied in many different forms, several illustrative embodiments are described herein with the understanding that this disclosure is to be considered as providing examples of the principles of the invention and such examples are not intended to limit the invention to the preferred embodiments described herein and/or illustrated herein. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well as the singular forms, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one having ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     In describing the invention, it will be understood that a number of techniques and steps are disclosed. Each of these has individual benefit and each can also be used in conjunction with one or more, or in some cases all, of the other disclosed techniques. Accordingly, for the sake of clarity, this description will refrain from repeating every possible combination of the individual steps in an unnecessary fashion. Nevertheless, the specification and claims should be read with the understanding that such combinations are entirely within the scope of the invention and the claims. 
     In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be evident, however, to one skilled in the art that the present invention may be practiced without these specific details. 
     The present disclosure is to be considered as an exemplification of the invention, and is not intended to limit the invention to the specific embodiments illustrated by the figures or description below. 
     The present invention will now be described by referencing the appended figures representing embodiments. 
       FIG. 1  is a left side view illustrating a vehicle  100  according to an embodiment.  FIG. 2  is a back view ¥ illustrating front row seats  110  and a periphery thereof. In this embodiment, the vehicle  100  is a four-wheel-drive vehicle for use in rough terrain, which is called, for example, a recreational off-highway vehicle (ROV). Alternatively, the vehicle  100  may be a straddle-type four-wheel-drive vehicle including a steering bar, which is called, for example, an all terrain vehicle (ATV). 
     The arrow F in  FIG. 1  indicates a forward direction of the vehicle  100 . In the following description, a front side, a rear side, an upper side, a lower side, a left side, and a right side respectively refer to a front side, a rear side, an upper side, a lower side, a left side, and a right side of the vehicle seen toward a steering wheel  103  from a driver seated on one of the front row seats  110 . 
     An engine unit  10  is arranged in a vicinity of a center of the vehicle  100  in a fore-and-aft direction and a right-and-left direction of the vehicle  100 . A front propeller shaft  122  extends forward from the engine unit  10 , and rotational power output from the engine unit  10  is transmitted to front wheels  120  through the front propeller shaft  122 . A rear propeller shaft  132  extends rearward from the engine unit  10 , and the rotational power output from the engine unit  10  is transmitted to rear wheels  130  through the rear propeller shaft  132 . The front propeller shaft  122  and the rear propeller shaft  132  are coupled to a propeller shaft  50  (described later in detail) that passes through the engine unit  10  in the fore-and-aft direction. 
     The engine unit  10  includes an engine  20  arranged in a rear portion thereof, and a gear transmission  40  arranged in a front portion thereof. The engine  20  is, for example, a water-cooled four-cycle parallel two-cylinder engine. In the engine  20 , a cylinder block  23  and a cylinder head  25  are arranged in inclined postures so as to be directed obliquely rearward and upward. The engine  20  is, for example, a dry sump engine, and a separate oil tank  90  is arranged behind the engine  20  to be coupled to the engine  20  through a pipe (not shown). 
     The plurality of front row seats  110  are arranged above or in a vicinity of the area above the engine unit  10  to be aligned in the right-and-left direction. The steering wheel  103  is arranged forward of the front row seats  110 . A plurality of rear row seats  115  are arranged rearward of the front row seats  110  to be aligned in the right-and-left direction. A cabin frame  105  is arranged to surround a space for occupants in which the front row seats  110 , the rear row seats  115 , and the steering wheel  103  are contained. A cargo bed  107  is arranged rearward of the rear row seats  115  and above the rear wheels  130 . The rear row seats  115  and the cargo bed  107  may be omitted. 
     The engine unit  10  is arranged so that at least a part of the engine unit  10  is located between the front row seats  110  and the rear row seats  115 . Each of the front row seats  110  includes a seat portion  111  and a backrest portion  112 , and each of the rear row seats  115  includes a seat portion  116  and a backrest portion  117 . Specifically, at least a part of the engine  20 , for example, the cylinder block  23  and the cylinder head  25  are located between the backrest portions  112  of the front row seats  110  and the seat portions  116  of the rear row seats  115 . 
     Further, the engine unit  10  is arranged so that at least a part of the engine unit  10  is located below the front row seats  110 . Specifically, the gear transmission  40  is located below the seat portions  111  of the front row seats  110 . A part of the engine unit  10  excluding the cylinder block  23  and the cylinder head  25  is located below the seat portions  111  of the front row seats  110 . Further, the engine unit  10  is arranged so that the propeller shaft  50  (described later in detail) passing through the engine unit  10  itself in the fore-and-aft direction is located near the center of the engine unit  10  in the right-and-left direction. The engine unit  10  may be arranged below the rear row seats  115 . 
       FIG. 3  is a left side view of the engine unit  10 . In  FIG. 3 , the propeller shaft  50  and a periphery thereof are illustrated cut in an up-and-down direction of the vehicle along a plane passing an axis of the propeller shaft  50  (that is, cut along line III-III of  FIG. 4 ). 
       FIG. 4  is a developed sectional view of the engine unit  10  taken along line IV-IV of  FIG. 3 . The line IV-IV is a polygonal line drawn by connecting a crankshaft  27 , a secondary shaft  43 , a transmission shaft  45 , and an output shaft  47  in the stated order. The arrow X 1  in  FIG. 4  indicates a leftward direction, and the arrow X 2  in  FIG. 4  indicates a rightward direction (with respect to the forward direction F). 
     The engine unit  10  includes the crankshaft  27 , the secondary shaft  43 , the transmission shaft  45 , and the output shaft  47  that extend in the right-and-left direction in parallel to one another. The crankshaft  27  is accommodated in a crankcase  21  of the engine  20 . The secondary shaft  43 , the transmission shaft  45 , and the output shaft  47  are accommodated in a transmission case configured to accommodate the transmission  40  therein. The crankcase  21  and the transmission case  41  are coupled to each other through intermediation of an adapter  60 . 
     Further, the engine unit  10  includes the propeller shaft  50  extending in the fore-and-aft direction. The propeller shaft  50  is arranged below the crankshaft  27 , the secondary shaft  43 , and the transmission shaft  45  to be orthogonal to the crankshaft  27 , the secondary shaft  43 , and the transmission shaft  45  in plan view. The propeller shaft  50  includes a rear shaft  52  passing through the crankcase  21  in the fore-and-aft direction, and a front shaft  54  passing through the transmission case  41  in the fore-and-aft direction. The rear shaft  52  and the front shaft  54  are coupled to each other. 
     The crankcase  21  includes an upper crankcase  21 A and a lower crankcase  21 B that are dividable in the up-and-down direction (direction perpendicular to an axis of the crankshaft  27 ) along a horizontal plane passing through the axis of the crankshaft  27 . The cylinder block  23  is joined to an upper portion of the crankcase  21 , and the cylinder head  25  is coupled to an upper portion of the cylinder block  23 . An oil pan  29  is coupled to a lower portion of the crankcase  21 . 
     Two cylinder bores  23   a  and  23   b  are formed in the cylinder block  23  to be aligned in the right-and-left direction. Pistons  24  and  24  are inserted into the cylinder bores  23   a  and  23   b , respectively. The pistons  24  and  24  are coupled to the crankshaft  27  through connecting rods  26  and  26 . 
     The crankshaft  27  includes left and right crankpins  71   a  and  71   b  to which the connecting rods  26  and  26  are coupled, respectively, crank webs  73 , which are coupled together to sandwich each of the left and right crankpins  71   a  and  71   b  therebetween, and crank journals  75 ,  76 , and  77 , which are coupled to the crank webs  73 . 
     An inside of the crankcase  21  is partitioned into two crank chambers  7   a  and  7   b  aligned in the right-and-left direction. The crankcase  21  includes three support wall portions  215 ,  216 , and  217  aligned in the right-and-left direction. The left crank chamber  7   a  is defined between the left support wall portion  215  and the middle support wall portion  216 , and the right crank chamber  7   b  is defined between the middle support wall portion  216  and the right support wall portion  217 . 
     The left crankpin  71   a , and the pair of crank webs  73  sandwiching the left crankpin  71   a  are accommodated in the left crank chamber  7   a , and the right crankpin  71   b , and the pair of crank webs  73  sandwiching the right crankpin  71   b  are accommodated in the right crank chamber  7   b . The left crank journal  75  is supported by the left support wall portion  215 , and the middle crank journal  76  is supported by the middle support wall portion  216 . The right crank journal  77  is supported by the right support wall portion  217 . 
     The crankshaft  27  further includes a right extending portion  79  extending rightward from the right support wall portion  217  of the crankcase  21 . A generator  11  is mounted to the right extending portion  79 . A generator cover  12  is mounted to a right side surface of the crankcase  21 , and a generator chamber  13 , configured to accommodate the generator  11  therein, is partitioned off in the crankcase  21 . 
     A gear  16  and a gear  19  are mounted on a portion of the right extending portion  79  of the crankshaft  27  between the support wall portion  217  and the generator  11 . The gear  16  is configured to drive, through a cam chain  15 , a cam  252  mounted to the cylinder head  25 . The gear  19  is configured to drive a pump unit (not shown) through a pump chain  18 . 
     The crankshaft  27  further includes a left extending portion  78  extending leftward from the left support wall portion  215  of the crankcase  21 . A centrifugal clutch  80  is arranged at a distal end portion of the left extending portion  78 . The centrifugal clutch  80  is arranged coaxially with the crankshaft  27 . A gap configured to position or accommodate the rear shaft  52  of the propeller shaft  50  therein, is formed between the left support wall portion  215  of the crankcase  21  and the centrifugal clutch  80 . 
     A primary shaft  28  is arranged on the left side of the left extending portion  78 , and the left extending portion  78  and the primary shaft  28  are coupled to each other through the centrifugal clutch  80 . The centrifugal clutch  80  includes a clutch inner  81  (e.g., inner clutch portion) and a clutch outer  83  (e.g., outer clutch portion). The clutch inner  81  is mounted to the left extending portion  78 , and the clutch outer  83  is mounted to the primary shaft  28 . The centrifugal clutch  80  transmits the rotational power of the crankshaft  27  to the primary shaft  28  in such a manner that an outer peripheral surface of the clutch inner  81  is pressed to an inner peripheral surface of the clutch outer  83  by a centrifugal force accompanied with rotation of the crankshaft  27 . 
     A clutch cover  85  is mounted to a left side surface of the crankcase  21 , and a clutch chamber  87 , configured to accommodate the centrifugal clutch  80  therein, is partitioned off in the crankcase  21 . An annular edge portion  289  is formed on the left side surface of the crankcase  21  to extend leftward and surround the left extending portion  78 . The clutch cover  85  is joined to (or extends to) the edge portion  289  to form the clutch chamber  87 . The primary shaft  28  extends leftward from the clutch cover  85 . A gap between the primary shaft  28  and the clutch cover  85  is sealed by a sealing member  88 . A proximal end portion of the primary shaft  28 , which is coupled to the clutch outer  83 , is supported by the clutch cover  85  through intermediation of a bearing  89 . 
     A belt type continuously variable transmission (CVT)  30  configured to transmit the rotational power from the engine  20  to the transmission  40  is arranged on the left side of the engine  20  and the transmission  40 . The rotational power of the primary shaft  28  coupled to the crankshaft  27  of the engine  20  through the centrifugal clutch  80  is continuously varied by the belt type CVT  30 , and then is transmitted to the secondary shaft  43  arranged in the transmission  40 . The belt type CVT  30  includes a drive pulley  33  mounted to the primary shaft  28 , a driven pulley  35  mounted to a left end portion of the secondary shaft  43 , and a rubber belt  37  wound around the drive pulley  33  and the driven pulley  35 . The belt  37  may be made of metal or a resin. 
     The belt type CVT  30  is accommodated in a CVT case  31  provided separately from the crankcase  21  and the transmission case  41 . The CVT case  31  includes a left CVT case  31 A and a right CVT case  31 B that are dividable in the right-and-left direction. An annular edge portion  239  is formed on the left side surface of the crankcase  21  to extend leftward and surround the edge portion  283  forming the clutch chamber  87 . A rear portion of the CVT case  31  is joined to the edge portion  239 . An edge portion  419  is also formed on a left side surface of the transmission case  41  to extend leftward and surround the secondary shaft  43 . A front portion of the CVT case  31  is joined to the edge portion  419 . 
     The drive pulley  33  includes a stationary sheave  331  fixed to the primary shaft  28 , and a movable sheave  333  mounted to the primary shaft  28  and movable in an axial direction. A weight  36  is arranged between the movable sheave  333  and a cam plate  34  fixed to the primary shaft  28 . The weight  36  is configured to move the movable sheave  333  in the axial direction by the centrifugal force accompanied with rotation of the primary shaft  28 . The distal end portion of the primary shaft  28  is supported through intermediation of a bearing  39  by a housing  32  formed inside the CVT case  31 . 
     The driven pulley  35  includes a stationary sheave  351  fixed to the secondary shaft  43 , and a movable sheave  353  mounted to the secondary shaft  43  and movable in the axial direction. A coil spring  38  applies pressure to the movable sheave  353  in a direction toward the stationary sheave  351 . 
     The transmission  40  changes the rotational power of the secondary shaft  43  to any one of a high mode, a low mode, and a reverse mode, and then transmits the rotational power to the transmission shaft  45 . The transmission  40  further transmits the rotational power, which has transmitted to the transmission shaft  45 , from the output shaft  47  to the propeller shaft  50 . The transmission  40  is accommodated in the transmission case  41  provided separately from the crankcase  21  and the CVT case  31 . The transmission case  41  includes a left transmission case  41 A and a right transmission case  41 B that are dividable in the right-and-left direction (direction of the axis). 
     A low drive gear  43   a , a high drive gear  43   b , and a reverse drive gear  43   c  are formed integrally with the secondary shaft  43 . A low driven gear  45   a , a high driven gear  45   b , and a reverse driven gear  45   c  are mounted to the transmission shaft  45  and are rotatable relative to one another. The low drive gear  43   a  and the low driven gear  45   a  mesh with each other, and the high drive gear  43   b  and the high driven gear  45   b  mesh with each other. Further, the reverse drive gear  43   c  and the reverse driven gear  45   c  respectively mesh with gears formed on a countershaft (not shown). 
     Dog clutches  451  and  453  are mounted to the transmission shaft  45  and are rotatable relative to one another in their axial direction. Further, a drive gear  45   d  is spline-connected to the transmission shaft  45 . When the dog clutch  451  meshes with the low driven gear  45   a , the transmission shaft  45  is rotated together with the low driven gear  45   a . When the dog clutch  453  meshes with the high driven gear  45   b , the transmission shaft  45  is rotated together with the high driven gear  45   b . When the dog clutch  451  meshes with the reverse driven gear  45   c , the transmission shaft  45  is rotated together with the reverse driven gear  45   c.    
     A driven gear  47   d , which meshes with the drive gear  45   d  of the transmission shaft  45 , is spline-connected to the output shaft  47 , and the rotational power of the transmission shaft  45  is transmitted to the output shaft  47 . Further, a bevel gear  47   e  is spline-connected to the output shaft  47 . A bevel gear  54   e , which meshes with the bevel gear  47   e  of the output shaft  47 , is spline-connected to the front shaft  54  of the propeller shaft  50  arranged in the transmission case  41 , and the rotational power of the output shaft  47  is transmitted to the front shaft  54 . 
     The front shaft  54  is arranged in the transmission case  41  to pass through the transmission case  41  in the fore-and-aft direction, and the rear shaft  52  is arranged in the crankcase  21  to pass through the crankcase  21  in the fore-and-aft direction. The front shaft  54  and the rear shaft  52  are coupled to each other, and thus construct the propeller shaft  50 . Specifically, a front end portion of the rear shaft  52  protruding forward from the crankcase  21  is inserted into and spline-connected to a rear end portion of the front shaft  54  protruding rearward from the transmission case  41 . 
     The rear end portion of the front shaft  54  is supported through intermediation of a bearing  493  by an annular shaft support portion  413  formed on a rear wall of the transmission case  41 . A gap between the rear end portion of the front shaft  54  and the shaft support portion  413  is sealed by a sealing member  495 . The front end portion of the rear shaft  52  is supported through intermediation of a bearing  283  by an annular shaft support portion  211  formed on a front wall of the crankcase  21 . A gap between the front end portion of the rear shaft  52  and the shaft support portion  211  is sealed by a searing member  285 . 
     An annular shaft support portion  411 , which protrudes forward, is formed on a front wall of the transmission case  41 . Annular cap  481  is fitted inside the shaft support portion  411 . A front end portion of the front shaft  54  is supported through intermediation of a bearing  483  by the cap  481  fitted inside the shaft support portion  411 . A gap between the front end portion of the front shaft  54  and the cap  481  is sealed by a sealing member  485 . A coupling member  541  is mounted to the front end portion of the front shaft  54 . The front propeller shaft  122  (see  FIG. 1 ) is coupled to the coupling member  541 . 
     An annular shaft support portion  213 , which protrudes rearward, is formed on a rear wall of the crankcase  21 . A rear end portion of the rear shaft  52  is supported by the shaft support portion  213  through intermediation of a bearing  293 . A gap between the rear end portion of the rear shaft  52  and the shaft support portion  213  is sealed by a sealing member  295 . A coupling member  521  is mounted to the rear end portion of the rear shaft  52 . The rear propeller shaft  132  (see  FIG. 1 ) is coupled to the coupling member  521 . 
       FIG. 5  to  FIG. 8  illustrate a top view, a left side view, a right side view, and a bottom view of a lower crankcase  21 B, respectively.  FIG. 8  is an illustration of a state in which a pump unit  700  is arranged in the lower crankcase  21 B.  FIG. 9  is a bottom view for illustrating the lower crankcase  21 B to which an oil pan  29  and a cover  290  are mounted. 
       FIG. 10  is an enlarged bottom view for illustrating a region of the oil pan  29 , which is covered with the cover  290 . In  FIG. 10 , only the covered region of the oil pan  29  is illustrated, and the illustration of a region other than the covered region is omitted.  FIG. 11  is a sectional view for illustrating the lower crankcase  21 B, to which the oil pan  29  and the cover  290  are mounted, when the lower crankcase  21 B is cut along line XI-XI of  FIG. 9 . 
       FIG. 12  is a sectional view for illustrating the pump unit  700  when the pump unit  700  is cut along line XII-XII of  FIG. 5 .  FIG. 13  is an enlarged sectional view for illustrating a generator chamber  13  and a periphery thereof when an engine  20  is taken along line XIII-XIII of  FIG. 3 . 
     As illustrated in  FIG. 5 , the lower crankcase  21 B includes three support wall portions  215 ,  216 , and  217  aligned in a right-and-left direction of a vehicle. A left crank chamber  7   a  is formed between the left support wall portion  215  and the middle support wall portion  216 , and a right crank chamber  7   b  is formed between the middle support wall portion  216  and the right support wall portion  217 . 
     A lower wall  221  is formed at a lower portion of the left crank chamber  7   a  formed between the left support wall portion  215  and the middle support wall portion  216 . The lower wall  221  is inclined forward and downward, and a through-hole  22   a  is formed in a front end portion of the lower wall  221  to pass through the lower wall  221  in an up-and-down direction of the vehicle. As a result of the inclination of the lower wall  221 , oil in the left crank chamber  7   a  is collected toward the through-hole  22   a  to flow downward through the through-hole  22   a.    
     A lower wall  222  is formed at a lower portion of the right crank chamber  7   b  formed between the middle support wall portion  216  and the right support wall portion  217 . The lower wall  222  is inclined forward and downward, and a through-hole  22   b  is formed in a front end portion of the lower wall  222  to pass through the lower wall  222  in the up-and-down direction. As a result of the inclination of the lower wall  222 , oil in the right crank chamber  7   b  is collected toward the through-bole  22   b  to flow downward through the through-hole  22   b.    
     An upper wall  227  is formed forward of the crank chambers  7   a  and  7   b . The upper wall  227  covers a relay chamber  205  (see, for example,  FIG. 11 ) for accommodating therein the pump unit  700  described later. Two mounting portions  227   a  and  227   b  are formed on the upper wall  227  to be apart from each other in the right-and-left direction. Pipes  98  and  99 , which are connected to an oil tank  90  (see  FIG. 1 ), are mounted to the mounting portions  227   a  and  227   b , respectively. 
     As illustrated in  FIG. 5  and  FIG. 6 , an edge portion  289  is formed on a left side surface of the lower crankcase  21 B, and extends leftward from the left support wall portion  215  to define a clutch chamber  87 . A through-hole  25   a  is formed in a front portion of the left support wall portion  215  and inside the edge portion  289  to pass through the left support wall portion  215  in the right-and-left direction and the up-and-down direction. The oil in the clutch chamber  87  flows through the through-hole  25   a  into the relay chamber  205  formed on a right side of the left support wall portion  215  and below the upper wall  227 . 
     As illustrated in  FIG. 5  and  FIG. 7 , an edge portion  229  is formed on a right side surface of the lower crankcase  21 B, and extends rightward from the right support wall portion  217  to define the generator chamber  13 . A through-hole  27   a  is formed in a front portion of the right support wall portion  217  and inside the edge portion  229  to pass through the right support wall portion  217  in the right-and-left direction. The oil in the generator chamber  13  flows through the through-hole  27   a  into the relay chamber  205  formed on a left side of the right support wall portion  217  and below the upper wall  227 . 
     Further, a shaft support hole  27   c  is formed in a front portion of the right support wall portion  217 , inside the edge portion  229 , and forward of the through-hole  27   a  to pass through the right support wall portion  217  in the right-and-left direction. A shaft portion  134  (see  FIG. 13 ) configured to drive the pump unit  700  described later is inserted into the shaft support hole  27   c.    
     As illustrated in  FIG. 8 , an annular lower edge  219 , which is joined to a peripheral edge of the oil pan  29 , is formed on a lower surface of the lower crankcase  21 B. Passage forming portions  224  and  225  are formed on the lower surface of the lower crankcase  21 B into semi-cylindrical shapes to be open downward. The passage forming portions  224  and  225  are joined to the oil pan  29 , and thus form oil passages (first passages)  91   a  and  91   b . The passage forming portions  224  and  225  are aligned in the right-and-left direction inside the annular lower edge  219  and cross a center portion in a fore-and-aft direction of the annular lower edge  219 . 
     A partition portion  226  configured to partition the oil passages  91   a  and  91   b  is formed between the passage forming portions  224  and  225  aligned in the right-and-left direction. However, the partition portion  226  may be omitted. 
     The relay chamber  205  is formed forward of the passage forming portions  224  and  225 , and the pump unit  700  is arranged in the relay chamber  205 . In this embodiment, the pump unit  700  includes two scavenge pumps  701  and  702 , and one feed pump  704 . The scavenge pumps  701  and  702 , and the feed pump  704  are aligned in the right-and-left direction so that the feed pump  704  is located at a rightmost position. 
     The through-hole  22   a  connected to the left crank chamber  7   a  is formed in a halfway portion of the left passage forming portion  224 . The oil in the left crank chamber  7   a  flows through the through-hole  22   a  into the left oil passage  91   a  formed by the left passage forming portion  224 , and then flows rightward in the left oil passage  91   a.    
     An opening  224   c  is formed in a left end portion of the left passage forming portion  224  to be open toward the relay chamber  205 . The through-hole  25   a  connected to the clutch chamber  87  is formed in a vicinity of the opening  224   c . The oil in the clutch chamber  87  flows into the relay chamber  205  through the through-hole  25   a , and also flows into the left oil passage  91   a  through the opening  224   c  formed in the vicinity of the through-hole  25   a  to flow rightward in the left oil passage  91   a.    
     The through-hole  22   b  connected to the right crank chamber  7   b  is formed in a halfway portion of the right passage forming portion  225 . The oil in the right crank chamber  7   b  flows through the through-hole  22   b  into the right oil passage  91   b  formed by the right passage forming portion  225 , and then flows leftward in the right oil passage  91   b.    
     An opening  225   c  is formed in a right end portion of the right passage forming portion  225  to generally bent forward and open toward the relay chamber  205 . The through-hole  27   a  connected to the generator chamber  13  is formed in a vicinity of the opening  225   c . The oil in the generator chamber  13  flows into the relay chamber  205  through the through-hole  27   a , and also flows into the right oil passage  91   b  through the opening  225   c  formed in the vicinity of the through-hole  27   a  to flow leftward in the right oil passage  91   b.    
     The oil flowing into the relay chamber  205  from the clutch chamber  87  through the through-hole  25   a , and the oil flowing into the relay chamber  205  from the generator chamber  13  through the through-hole  27   a  are temporarily accumulated in the relay chamber  205 , but finally flow into the oil passages  91   a  and  91   b  through the openings  224   c  and  225   c . The oil that oozes out of the pump unit  700  similarly flows into the oil passages  91   a  and  91   b  through the openings  224   c  and  225   c.    
     As illustrated in  FIG. 9 , the oil pan  29  is mounted to a lower surface of the lower crankcase  21 B. The oil pan  29  is formed into a substantially plate-like shape, and the oil pan  29  itself does not have a structure capable of accumulating the oil (see  FIG. 11 ). Further, the cover  290  is mounted to a part of a lower surface of the oil pan  29 . 
     As illustrated in  FIG. 8  to  FIG. 11 , a plurality of through-holes  29   a  to  29   d  are formed in the region of the oil pan  29 , which is covered with the cover  290 . The cover  290  is formed into a dish-like shape having a dent (e.g., protruding portion). The cover  290  is joined to the oil pan  29 , and thus forms oil passages (second passages)  93   a  and  93   b.    
     Specifically, when the oil pan  29  and the cover  290  are joined to each other, the left oil passage  93   a  is formed between the left rear through-hole  29   a  and the left front through-hole  29   c  among the four through-holes  29   a  to  29   d , and the right oil passage  93   b  is formed between the right rear through-hole  29   b  and the right front through-hole  29   d  among the four through-holes  29   a  to  29   d.    
     The left oil passage  93   a  is coupled to a downstream side of the left oil passage  91   a  formed by the left passage forming portion  224  of the lower crankcase  21 B and the oil pan  29 . The left rear through-hole  29   a  is connected to a right end portion of the left oil passage  91   a . The left scavenge pump  701  is coupled to a downstream side of the left oil passage  93   a  through a pipe  707 . 
     The oil pan  29  includes a tubular portion  295  (see  FIG. 11 ) extending upward and having the left front through-hole  29   c  formed therein. An upper portion of the pipe  707  is inserted into a suction port  731  of the left scavenge pump  701 , and a lower portion of the pipe  707  is inserted into the tubular portion  295 . The left front through-hole  29   c  is located directly below the suction port  731  of the left scavenge pump  701 , and the pipe  707  extends in the up-and-down direction. The right front through-hole  29   d  also has a similar configuration. 
     The oil flowing rightward in the left oil passage  91   a  flows into the left oil passage  93   a  through the through-hole  29   a  before reaching the partition portion  226 , and further flows from the left oil passage  93   a  through the pipe  707  to be sucked into the left scavenge pump  701 . 
     The right oil passage  93   b  is coupled to a downstream side of the right oil passage  91   b  formed by the right passage forming portion  225  of the lower crankcase  21 B and the oil pan  29 . The right rear through-hole  29   b  is connected to a left end portion of the right oil passage  91   b . The right scavenge pump  702  is coupled to a down stream side of the right oil passage  93   b  through a pipe  72 . 
     The oil flowing leftward in the right oil passage  91   b  flows into the right oil passage  93   b  through the through-hole  29   b  before reaching the partition portion  226 , and further flows from the right oil passage  93   b  through the pipe  708  to be sucked into the right scavenge pump  702 . 
     A recessed portion  291  is formed in a range of the oil pan  29 , which contains both the left front through-hole  29   c  and the right front through-hole  29   d . A strainer  92  is arranged inside the recessed portion  291 , and covers the two through-holes  29   c  and  29   d . The oil flowing in the oil passages  93   a  and  93   b  is sucked into the scavenge pumps  701  and  702  after filtered by the strainer  92 . 
     As illustrated in  FIG. 12 , the pump unit  700  includes the two scavenge pumps  701  and  702  and the one feed pump  704  arranged in the stated order from a left side of the vehicle. The scavenge pumps  701  and  702  and the feed pump  704  are integrated with one another by a common housing  730 , and are driven by a common pump driving shaft  709 . 
     The left scavenge pump  701  includes an inner rotor  711  fixed to the pump driving shaft  709 , and an outer rotor  713  retained in the housing  730 . In accordance with relative rotation of the inner rotor  711  and the outer rotor  713 , the left scavenge pump  701  sucks the oil from the suction port  731  into a suction chamber  715 , feeds the oil in the suction chamber  715  into a discharge chamber  737 , and discharges the oil in the discharge chamber  737  from a discharge port  733 . 
     The right scavenge pump  702  includes an inner rotor  721  fixed to the pump driving shaft  709 , and an outer rotor  723  retained in the housing  730 . In accordance with relative rotation of the inner rotor  721  and the outer rotor  723 , the right scavenge pump  702  sucks the oil from the suction port  732  into a suction chamber  725 , feeds the oil in the suction chamber  725  into the discharge chamber  737 , and discharges the oil in the discharge chamber  737  from the discharge port  733 . 
     As described above, the pipe  707  coupled to the left oil passage  93   a  is inserted into the suction port  731  of the left scavenge pump  701  (see  FIG. 8  to  FIG. 11 ). Further, the pipe  708  coupled to the right oil passage  93   b  is inserted into the suction port  732  of the right scavenge pump  702 . 
     The common discharge chamber  737  and the common discharge port  733  are formed for the scavenge pumps  701  and  702 . That is, the oil fed out of the suction chamber  715  of the left scavenge pump  701 , and the oil fed out of the suction chamber  725  of the right scavenge pump  702  flow together in the discharge chamber  737 , and then are discharged from the discharge port  733 . 
     The discharge port  733  for the scavenge pumps  701  and  702  is fitted to the mounting portion  227   a  formed on the upper wall  227  that covers the relay chamber  205 , and the discharge port  733  is coupled to the pipe  98 . The oil discharged from the discharge port  733  flows through the pipe  98 , and reaches the oil tank  90  (see  FIG. 1 ) to be accumulated in the oil tank  90 . 
     The feed pump  704  includes an inner rotor  741  fixed to the pump driving shaft  709 , and an outer rotor  743  retained in the housing  730 . In accordance with relative rotation of the inner rotor  741  and the outer rotor  743 , the feed pump  704  sucks the oil from a suction port  734  into a suction chamber  745 , feeds the oil in the suction chamber  745  into a discharge chamber  747 , and discharges the oil in the discharge chamber  747  from a discharge port  736 . 
     The suction port  734  of the feed pump  704  is fitted to the mounting portion  227   b  formed on the upper wall  227  that covers the relay chamber  205 , and the suction port  734  is coupled to the pipe  99 . The oil accumulated in the oil tank  90  (see  FIG. 1 ) is sucked through the pipe  99  by the feed pump  704 . 
     As illustrated in  FIG. 13 , rotational power of a crankshaft  27  is transmitted to the pump driving shaft  709 . A right extending portion  79  of the crankshaft  27 , and the shaft portion  134  rotatably supported in the shaft support hole  27   c  are arranged in the generator chamber  13 . 
     A left end portion of the shaft portion  134  enters the relay chamber  205 , and is coupled to a right end portion  709   c  of the pump driving shaft  709  of the pump unit  700 . A right end portion of the shaft portion  134  is rotatably coupled to a shaft portion  137  supported by a generator cover  12 . A gear  135  is formed on a halfway portion of the shaft portion  134 . 
     A pump chain  18  is wound around a gear  19  formed on the right extending portion  79  of the crankshaft  27 , and around the gear  135  formed on the shaft portion  134  coupled to the pump driving shaft  709 . With this configuration, the rotational power of the crankshaft  27  is transmitted to the pump driving shaft  709 . 
       FIG. 14  is a schematic view for illustrating an oil-lubricated path for the engine  20  (namely, engine lubrication system  200 ).  FIG. 15  is an enlarged schematic view for illustrating an oil collecting region in the oil-lubricated path for the engine  20 . 
     As illustrated in  FIG. 15 , the oil in the left crank chamber  7   a  flows through the through-hole  22   a  into the left oil passage  91   a  (first passage) formed by the left passage forming portion  224  and the oil pan  29 . The oil flowing into the left oil passage  91   a  further flows into the left oil passage  93   a  (second passage) formed by the oil pan  29  and the cover  290 . The oil flowing into the left oil passage  93   a  is sucked through the pipe  707  into the left scavenge pump  701 . 
     Further, the oil in the right crank chamber  7   b  flows through the through-hole  22   b  into the right oil passage  91   b  (first passage) formed by the right passage forming portion  225  and the oil pan  29 . The oil flowing into the right oil passage  91   b  further flows into the right oil passage  93   b  (second passage) formed by the oil pan  29  and the cover  290 . The oil flowing into the right oil passage  93   b  is sucked through the pipe  708  into the right scavenge pump  702 . 
     Further, the oil in the clutch chamber  87  flows into the relay chamber  205  through the through-hole  25   a . The oil flowing into the relay chamber  205  through the through-hole  25   a  is mostly sucked into the left oil passage  91   a  (first passage), and then is sucked from the left oil passage  93   a  (second passage) through the pipe  707  into the left scavenge pump  701 . The oil flowing into the relay chamber  205  through the through-hole  25   a  may be sucked into the right oil passage  91   b.    
     Further, the oil in the generator chamber  13  flows into the relay chamber  205  through the through-hole  27   a . The oil flowing into the relay chamber  205  through the through-hole  27   a  is mostly sucked into the right oil passage  91   b  (first passage), and then is sucked from the right oil passage  93   b  (second passage) through the pipe  708  into the right scavenge pump  702 . The oil flowing into the relay chamber  205  through the through-hole  27   a  may be sucked into the left oil passage  91   a.    
     The present invention is not limited to this configuration. For example, as illustrated in  FIG. 16 , the through-hole  25   a  of the clutch chamber  87  and the left oil passage  91   a  may be connected to each other so that the oil in the clutch chamber  87  flows directly into the left oil passage  91   a . Alternatively, the through-hole  27   a  of the generator chamber  13  and the right oil passage  91   b  may be connected to each other so that the oil in the generator chamber  13  flows directly into the right oil passage  91   b.    
     As illustrated in  FIG. 14 , the scavenge pumps  701  and  702  suck the oil, and feed the sucked oil through the pipe  98  into the oil tank  90  arranged outside the engine  20 . 
     Meanwhile, the feed pump  704  sucks the oil accumulated in the oil tank  90 . A relief valve  901  is arranged in parallel to the feed pump  704 , and a check valve  902  is arranged downstream of the feed pump  704 . The oil discharged from the feed pump  704  passes through an oil cleaner  903  and an oil cooler  904 , and then is fed into components of the engine  20 . 
     Specifically, the oil discharged from the feed pump  704  is supplied to crank journals  75  to  77  of the crankshaft  27 , and is supplied to crankpins  71   a  and  71   b  arranged in the crank chambers  7   a  and  7   b , cylinder bores  23   a  and  23   b , a balancer shaft  907 , camshafts  908  and  909 , and the like. In addition, the oil is supplied to a generator  11  arranged in the generator chamber  13 , and to a centrifugal clutch  80  arranged in the clutch chamber  87 . 
     As described above, in this embodiment, at least a portion of each of the oil passages  91   a  and  91   b  is formed by the lower crankcase  21 B, and the oil is directly sucked from the oil passages  91   a  and  91   b  that allow inflow of the oil in the crank chambers  7   a  and  7   b . Thus, an oil collection efficiency can be increased. 
     Further, in this embodiment, the pump unit  700  is accommodated in crankcase  21 . Thus, the pump unit  700  can be protected from a flying object such as a stone. Further, as compared to a case of arranging the pump unit  700  outside the crankcase  21 , path lengths from the crank chambers  7   a  and  7   b  to the scavenge pumps  701  and  702  are reduced. Accordingly, suction resistance can be reduced, and the oil collection efficiency can be increased. 
     Further, in this embodiment, the oil flowing from the clutch chamber  87  and the generator chamber  13  into the relay chamber  205  further flows into the oil passages  91   a  and  91   b . Accordingly, the oil collection efficiency can be further increased. 
     Further, in this embodiment, the pump unit  700  is accommodated or positioned in the relay chamber  205 . In general, when priority is given to sealing performance to prevent leakage of the oil, it is necessary to increase a size of the pump. However, in this embodiment, the pump unit  700  is accommodated in the relay chamber  205  so that leakage of the oil can be somewhat permitted. Accordingly, the pump unit  700  can be downsized. 
     Further, in this embodiment, the scavenge pumps  701  and  702  and the feed pump  704  are included in the pump unit  700 . Also with this configuration, the pump unit  700  can be downsized. 
     Further, in this embodiment, the scavenge pumps  701  and  702  and the feed pump  704  are driven by the common pump driving shaft  709 . Also with this configuration, the pump unit  700  can be downsized. 
     Further, in this embodiment, the two crank chambers  7   a  and  7   b  corresponding to two cylinders, and the two oil passages  91   a  and  91   b  corresponding to the two crank chambers  7   a  and  7   b  are formed. With this configuration, there can be suppressed an influence of an air pressure difference between the crank chambers  7   a  and  7   b  resulting from a phase difference between pistons  24 . Further, the path lengths from the crank chambers  7   a  and  7   b  to the scavenge pumps  701  and  702  can be reduced. 
     Further, in this embodiment, the two scavenge pumps  701  and  702  corresponding to the two oil passages  91   a  and  91   b  are arranged. With this configuration, there can be suppressed the influence of the air pressure difference between the crank chambers  7   a  and  7   b  resulting from the phase difference between the pistons  24 . The present invention is not limited to this configuration. The oil passages  91   a  and  91   b  may be formed integrally with each other, or one scavenge pump may be used in place of the scavenge pumps  701  and  702 . 
     Further, in this embodiment, the oil passages  91   a  and  91   b  are formed by the lower crankcase  21 B and the oil pan  29  mounted to the lower surface of the lower crankcase  21 B. With this configuration, the oil passages  91   a  and  91   b  can be formed at lower positions. 
     Further, in this embodiment, there are provided the oil passages  91   a  and  91   b  formed by the lower crankcase  21 B and the oil pan  29 , and the oil passages  93   a  and  93   b  formed by the oil pan  29  and the cover  290  and coupled to the downstream sides of the oil passages  91   a  and  91   b , respectively. With this configuration, maintenance can be performed on the oil passages  91   a ,  91   b ,  93   a , and  93   b  only by dismounting the cover  290  from the oil pan  29 . 
     Further, in this embodiment, the scavenge pumps  701  and  702  suck the oil from the oil passages  93   a  and  93   b . Thus, the scavenge pumps  701  and  702  suck the oil from a position lower than the oil passages  91   a  and  91   b  formed upstream of the oil passages  93   a  and  93   b . Accordingly, the oil collection efficiency can be increased. 
     Further, in this embodiment, the pipe  707  is arranged to connect the oil passage  93   a  and the scavenge pump  701  to each other, and the pipe  708  is arranged to connect the oil passage  93   b  and the scavenge pump  702  to each other. With this configuration, the oil is directly sucked from the oil passages  93   a  and  93   b . Accordingly, the oil collection efficiency can be increased. 
     Further, in this embodiment, the strainer  92  is arranged to cover the through-holes  29   a  to  29   d  formed in the oil pan  29 . With this configuration, debris clogging the strainer  92  can be removed only by dismounting the cover  290  from the oil pan  29 . 
     Further, in this embodiment, at least a part of the engine  20  is located between front row seats  110  in plan view, and is located below the front row seats  110  in side view (see  FIG. 1  and  FIG. 2 ). In the illustrated example, the crankcase  21  of the engine  20  is located between the front row seats  110  in plan view, and is located below the front row seats  110  in side view. Specifically, the crankcase  21  is located below a center console  119  arranged between the front row seats  110 . Further, the crankcase  21  is located below seat portions  111  of the front row seats  110 . In this embodiment, the engine  20  is a dry sump type engine, and the engine  20  can be downsized by providing the oil tank  90  separately. Accordingly, even in a layout in which at least a part of the engine  20  is located between the front row seats  110  in plan view and located below the front row seats  110  in side view, a minimum ground clearance of a vehicle  100  is easily ensured. 
     Further, in this embodiment, the scavenge pumps  701  and  702  and the feed pump  704  are accommodated in the engine  20 . With this configuration, as described above, the scavenge pumps  701  and  702  and the feed pump  704  can be protected and downsized. As a result, the engine  20  can be also downsized. Therefore, even in the layout in which at least a part of the engine  20  is located between the front row seats  110  in plan view and located below the front row seats  110  in side view, the minimum ground clearance of the vehicle  100  is easily ensured. 
     Further, in this embodiment, the engine  20  is arranged astride a center of the vehicle  100  in the right-and-left direction of the vehicle (see  FIG. 2 ). The center of the vehicle  100  in the right-and-left direction of the vehicle is located, for example, between the front row seats  110 . Further, the engine  20  may be arranged astride a center of the vehicle  100  in the fore-and-aft direction of the vehicle (see  FIG. 1 ). The center of the vehicle  100  in the fore-and-aft direction of the vehicle is located, for example, between front wheels  120  and rear wheels  130 . The center console  119  is arranged between the front row seats  110  and between the front wheels  120  and the rear wheels  130 , and the engine  20  is arranged below the center console  119 . With this configuration, even when the crankcase  21  includes an upward projecting portion or a structure such as an intake pipe is arranged above the engine, the upward projecting portion or the structure can be avoided by modifying a shape of a lower surface of the center console  119 . 
     Further, in this embodiment, the oil tank  90  is arranged at a side of the engine  20  (see  FIG. 1 ). Herein, the “side” means a side in a horizontal direction, and encompasses not only a side in the right-and-left direction but also a side in the fore-and-aft direction. In the illustrated example, the oil tank  90  is arranged behind the engine  20 . Alternatively, the oil tank  90  may be arranged in front of the engine  20 . When the oil tank  90  is thus arranged at the side of the engine  20 , a length in the up-and-down direction of the entire lubrication system including the engine  20  and the oil tank  90  can be reduced. Thus, the minimum ground clearance is easily secured and a projection into a cabin space can be prevented. In addition, when the oil tank  90  is arranged in front of or behind the engine  20 , a width in the right-and-left direction of the entire lubrication system including the engine  20  and the oil tank  90  can be also reduced. Accordingly, the lubrication system can be arranged in a vicinity of the center of the vehicle  100  in the right-and-left direction. 
     Further, in this embodiment, the engine  20  is the dry sump type engine, and the engine  20  can be downsized by providing the oil tank  90  separately. Accordingly, even when the engine  20  is a parallel two-cylinder engine, upsizing of the engine  20  can be prevented. 
     Although the present invention has been illustrated and described herein with reference to embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention, are contemplated thereby, and are intended to be covered by the following claims.