Abstract:
An internal combustion engine can comprise a crankcase, and a crankshaft rotatably supported in the crankcase. The crankshaft includes a drive sprocket attached thereto. A cam chain engages the drive sprocket, and a cam chain chamber houses at least a part of the drive sprocket and cam chain therein. The cam chain chamber is configured to pool oil in a lower portion thereof. A balancer is coupled to the crankshaft and is configured to be rotated by rotational power transmitted from the crankshaft. The balancer is also disposed within the cam chain chamber, and is configured to splash oil pooled in the cam chain chamber during the rotation thereof. The engine also comprises a wall portion disposed in the cam chain chamber. The wall portion is configured to cover an upper portion of the balancer, and is disposed adjacent to a periphery of the balancer.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    The present invention relates to internal combustion engines. In particular, engines having pooled oil and which rely, at least in part, on internal lubrication at least in part 
         [0003]    2. Description of the Related Art 
         [0004]    An internal combustion engine having the following structure is known from Japanese Patent Publication No. 2007-291950 (Japan &#39;950). Specifically, in the internal combustion engine, a cam chain chamber which houses a drive sprocket and a part of a cam chain wound around the drive sprocket, is formed between a crankcase and a cover which is connected to the crankcase and covers a side of the crankcase. The cam chain chamber is formed also to be capable of pooling oil in a lower portion thereof. In addition, a balancer is housed in the cam chain chamber and arranged at a position where the balancer is capable of splashing the oil pooled in the lower portion inside the cam chain chamber. 
         [0005]    Meanwhile, the oil pooled in the lower portion of the cam chain chamber is sucked in by an oil pump, and then is supplied from the oil pump to a lubricating portion of the internal combustion engine. When oil splashed by the rotation of the balancer falls down on an oil sump, bubbles are generated in the oil in the oil sump. As a result, air is likely to be mixed into the oil which is to be sucked by the oil pump. 
       SUMMARY 
       [0006]    In one embodiment, an internal combustion engine includes a crankcase and a crankshaft rotatably supported in the crankcase. The crankshaft includes a drive sprocket attached thereto. A cam chain engages the drive sprocket, and a cam chain chamber houses at least a part of the drive sprocket and cam chain therein. The cam chain chamber is configured to pool oil in a lower portion thereof. A balancer is coupled to the crankshaft and is configured to be rotated by rotational power transmitted from the crankshaft. The balancer is also disposed within the cam chain chamber, and is configured to splash oil pooled in the cam chain chamber during the rotation thereof. The engine also includes a wall portion disposed in the cam chain chamber, with the wall portion configured to cover an upper portion of the balancer. The wall portion is disposed is adjacent to a periphery of the balancer. 
         [0007]    In another embodiment, the wall portion can include a cutout therein, with the cutout configured to discharge oil between the balancer and the wall portion therethrough. 
         [0008]    In other embodiments, the cutout can be disposed above an uppermost portion of a rotational trajectory of an outermost periphery of the balancer. 
         [0009]    The crankcase can include a pair of case halves connected to each other at a matching interface along a plain orthogonal to an access of the crankshaft. At least one of a plurality of bolts fastening the case halves together are configured so as to partially to meet the cutout. 
         [0010]    A guide supporting portion can be formed integrally on the crankcase adjacent side of the balancer, wherein the guide supporting portion is recessed in a J shape into which at an end portion of a cam chain guide, guiding the cam chain is supported. The wall portion can be formed integrally on the crankcase so as to be continuously connected to the guide supporting portion. 
         [0011]    According to embodiments of the invention, the balancer is covered at least from above by the wall portion adjacent to the outer periphery of the balancer. Accordingly, the oil splashed by the rotation of the balancer is caused to hit the wall portion, thereby being collected. The oil thus collected falls in drops from the wall portion, so that babbles are unlikely to be generated in the oil. As a result, air is unlikely to be mixed into the oil which is to be sucked in by an oil pump. 
         [0012]    In some embodiments of the invention, a part of oil pooled between the balancer and the wall portion is discharged through the cutout to the side of the wall portion, so that the rotational friction of the balancer can be reduced. 
         [0013]    According to another embodiment, the cutout is arranged above the uppermost portion of the rotational trajectory of the outermost periphery of the balancer. Accordingly, the oil splashed by the balancer can be prevented from reaching directly the cutout and then coming out to the side of the wall portion. 
         [0014]    In some embodiments, at least one of the plurality of bolts with which the pair of case halves are fastened to each other is arranged in such a manner as to partially meet the cutout. Accordingly, the flexibility in the layout of the bolt can be enhanced with the wall portion not interfering with the layout of the bolt. 
         [0015]    Furthermore, according to some embodiments, the wall portion is provided integrally on the crankcase in such a manner as to be continuously connected to the guide supporting portion into which an end portion of the cam chain guide is fitted to be supported. Accordingly, the guide supporting portion is provided with the function to collect the oil splashed by the balancer, whereby the effect of collecting oil can be enhanced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a vertical cross-sectional side view of essential parts of an internal combustion engine according to an embodiment of the invention. 
           [0017]      FIG. 2  is a cross-sectional view taken along the line  2 - 2  in  FIG. 1 . 
           [0018]      FIG. 3  is a cross-sectional view taken along the line  3 - 3  in  FIG. 2 . 
           [0019]      FIG. 4  is a cross-sectional view taken along the line  4 - 4  in  FIG. 2 . 
           [0020]      FIG. 5  is a perspective view of a left case half in accordance with an embodiment of the engine. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Hereinafter, embodiments of the present invention will be described in detail on the basis of the accompanying drawings. 
         [0022]    With reference to  FIG. 1  to  FIG. 5 , Embodiment 1 of the present invention will be described. In  FIG. 1 , an engine main body  13  of a single-cylinder four-cycle internal combustion engine E is mounted on a motorcycle in such a manner that an axis of a crankshaft  14  is aligned in a right-left direction of the motorcycle. The internal combustion engine E includes an output shaft  20  protruding to the left of a rear portion of the engine main body  13 . Transmission  23 , which can include an endless chain  22 , is provided between an outer end portion of the output shaft  20  and an axle (not illustrated) of a rear wheel. Rotational power from the internal combustion engine E is transmitted to the rear wheel via the transmission or transmission means  23 . 
         [0023]    The engine main body  13  can include a crankcase  25 , a cylinder block  26  connected to the crankcase  25 , a cylinder head  27  connected to the cylinder block  26 , and a head cover (not illustrated) connected to the cylinder head  27 . 
         [0024]    In this example, the crankcase  25  in which the crankshaft  14  is rotatably supported is formed of a right case half  29  and a left case half  30 , which are connected to each other at a matching interface  31  along a plane orthogonal to the axis of the crankshaft  14 . The right case half  29  and the left case half  30  are arranged respectively on the right and left sides when mounted on the motorcycle. Both of the case halves  29  and  30  can be formed, in this example, of an aluminum alloy. Further, a crank chamber  32  and a transmission chamber  33  are formed in the crankcase  25  while being separated from each other by a partition wall  34 . The crank chamber  32  houses portions of the crankshaft  14 , and the transmission chamber  33  houses a constant-mesh transmission  35 . 
         [0025]    As noted above, portions of the crankshaft  14  are housed in the crank chamber  32 . A piston  36  is slidably fitted in the cylinder block  26 , and a large end of a connecting rod  37  continuous with the piston  36  is coupled to the crankshaft  14  with a crankpin  38 . 
         [0026]    The transmission  35  can be made up of a plurality of speed gear trains which can be selectively established, for example, first to fifth speed gear trains G 1 , G 2 , G 3 , G 4 , and G 5 , provided between a main shaft  40  and the output shaft  20 . The main shaft  40  has an axis parallel to the crankshaft  14  and is rotatably supported in the right and left case halves  29  and  30 . The output shaft  20  has an axis parallel to the main shaft  40  and is rotatably supported in the case halves  29  and  30 . 
         [0027]    A sprocket  42  which constitutes a part of the transmission  23  is fixed on an end portion of the output shaft  20 , the end portion protruding from the left case half  30 . The chain  22  is wound around the sprocket  42 . In addition, a sprocket cover  39  which covers the sprocket  42  is attached to the left case half  30 . 
         [0028]    In a state where the engine main body  13  is mounted on the motorcycle, the right end portions respectively of the crankshaft  14  and the main shaft  40  protrude from the right case half  29 . A starter clutch  43  is mounted on the right end portion of the main shaft  40 . The starter clutch  43  switches between connection and disconnection of power between the crankshaft  14  and the main shaft  40 . The rotational power of the crankshaft  14  is transmitted to an input member  44  of the starter clutch  43  via a first reduction gear  45 . The first reduction gear  45  is formed of a drive gear  46  and a driven gear  47 . The drive gear  46  is fixed on the right end portion of the crankshaft  14 . The driven gear  47  is supported on the main shaft  40  in such a manner as to be rotatable relative to the main shaft  40  while meshing with the drive gear  46 . The driven gear  47  is coupled to the input member  44 , which is supported on the main shaft  40  in such a manner as to be rotatable relative to the main shaft  40 . 
         [0029]    A right cover  48  can be fastened to the right case half  29  in such a manner as to cover the first reduction gear  45 . The right cover  48  constitutes a part of the engine main body  13  while having an opening portion  50  through which a part of the starter clutch  43  comes out. A clutch cover  49  for covering the starter clutch  43  is fastened to the right cover  48  in such a manner as to close the opening portion  50 . 
         [0030]    Referring to  FIG. 2  and  FIG. 3 , in the state where the engine main body  13  is mounted on the motorcycle, the left end portion of the crankshaft  14  protrudes from the left case half  30 . A rotor  56  is fixed on the left end portion of the crankshaft  14 . A stator  55  is fixed in an electric-generator cover  53  which is fastened to the left case half  30  while constituting a part of the engine main body  13 . The stator  55  and the rotor  56  constitute an electric generator  54 . 
         [0031]    A cam chain chamber  57  is formed between the left case half  30  of the crankcase  25  and the electric-generator cover  53 . A drive sprocket  58  is fixed on the crankshaft  14  at a position inside the cam chain chamber  57 . An endless cam chain  59  is wound around the drive sprocket  58  while a part of the cam chain  59  is housed in the cam chain chamber  57 . A driven sprocket (not illustrated) is fixed on a cam shaft (not illustrated) rotatably supported in the cylinder head  27  while the cam chain  59  is wound around the driven sprocket. The drive sprocket  58 , the cam chain  59 , and the driven sprocket constitute a timing transmission system  61  which transmits the rotational power of the crankshaft  14  to the cam shaft while reducing the rotational speed thereof by ½. A cam chain passage  63  is formed in the cylinder block  26  and the cylinder head  27  in such a way as to allow the cam chain  59  to run therethrough. The cam chain passage  63  extends in the up-down direction with a lower end portion thereof communicating with the cam chain chamber  57 . 
         [0032]    The crankshaft  14  and the drive sprocket  58  each rotate in a direction indicated by the arrow  64  in  FIG. 2 . Such a rotation of the drive sprocket  58  causes the cam chain  59  to run between the drive sprocket  58  and the driven sprocket. A cam chain guide  65  guides the cam chain  59  at the tension side thereof. A guide supporting portion  66  into which an end portion of the cam chain guide  65  is fitted to be supported is formed integrally on the left case half  30  of the crankcase  25 . The guide supporting portion  66  has a shape recessed in a substantially “J” shape. 
         [0033]    Moreover, a tensioner  67  is rotatably supported at an end portion thereof on the left case half  30  of the crankcase  25  by means of a spindle  68 . The tensioner  67  is designed to come into contact with the outer periphery of the cam chain  59  at the slack side thereof, and to thereby tension the cam chain  59 . The other end side of the tensioner  67  is resiliently biased toward the cam chain  59  by a tensioner lifter (not illustrated) attached to the cylinder head  27 . 
         [0034]    Referring to  FIG. 3 , a first oil sump  71  communicating with a lower portion of the crank chamber  32  is formed in a lower portion of the crankcase  25 . In addition, a second oil sump  72  and a third oil sump  74  are formed in the lower portion of the crankcase  25  and the lower portion inside the cam chain chamber  57 . A reed valve  73  designed to open and close in accordance with a variation in pressure inside the crank chamber  32  is interposed between the first oil sump  71  and the second oil sump  72 . An oil strainer  75  is interposed between the second oil sump  72  and the third oil sump  74 . The inside of the second oil sump  72  is open to the atmosphere via an unillustrated breather passage, so that the pressure inside the second oil sump  72  is equal to the atmospheric pressure. In addition, the reed valve  73  is sandwiched and held between the right case half  29  and the left case half  30 . Moreover, the oil strainer  75  is sandwiched and held between the left case half  30  and the electric-generator cover  53 . 
         [0035]    Oil in the third oil sump  74  is pumped up by an oil pump  76 . The oil pump  76  can formed as a trochoid pump. In this example, the pump can include an inner rotor  78  fixed on an inner end of a pump shaft  77 , and an outer rotor  79  meshing with the inner rotor  78 . The oil pump  76  is provided between the right and left case halves  29  and  30  of the crankcase  25  in such a manner as to be disposed forward of the crankshaft  14  when the engine main body  13  is mounted on the motorcycle. 
         [0036]    A balancer shaft  80  is rotatably supported in the right and left case halves  29  and  30  of the crankcase  25 . The balancer shaft  80  has an axis parallel to the crankshaft  14  and is arranged forward of the crankshaft  14 . A first drive gear  81  is provided on a protruding portion of the crankshaft  14 , the protruding portion protruding from the right case half  29  while a first driven gear  82  is provided on a protruding portion of the balancer shaft  80 , the protruding portion protruding from the right case half  29 . The first driven gear  82  meshes with the first drive gear  81 , and accordingly, the balancer shaft  80  is rotated by power transmitted from the crankshaft  14 . 
         [0037]    In addition, a water pump  85  can be arranged above the balancer shaft  80 . The water pump  85  has a pump housing  84 , with the right cover  48  connected to the right case half  29  from the outer side, and a pump cover  83  fastened to an outer surface of the right cover  48 . In the example, the water pump  85  includes a pump shaft  86  which is parallel to the balancer shaft  80 . 
         [0038]    The pump shaft  86  can penetrate, fluid-tightly and rotatably, the right cover  48  of the pump housing  84 . Rotating vanes  87  are firmly fixed coaxially on one end portion of the pump shaft  86  inserted into the pump housing  84 . The pump shaft  86  is rotatably supported at the other end portion thereof by the right case half  29 . 
         [0039]    A second drive gear  88  aligned with the first drive gear  81  is fixed on a protruding portion of the balancer shaft  80 , the protruding portion protruding from the right case half  29 . A second driven gear  89  meshing with the second drive gear  88  is fixed on the pump shaft  86 . Accordingly, the rotational power from the crankshaft  14  is transmitted also to the pump shaft  86  of the water pump  85 . 
         [0040]    A third drive gear  90  is fixed on a protruding portion of the balancer shaft  80 , the protruding portion protruding from the left case half  30 . A third driven gear meshing with the third drive gear  90  is fixed on a protruding end portion of the pump shaft  77  of the oil pump  76 , the protruding end portion protruding from the left case half  30 . Accordingly, the rotational power from the crankshaft  14  is transmitted to the pump shaft  77  of the oil pump  76  via the balancer shaft  80 . 
         [0041]    A balancer  93  arranged inside the cam chain chamber  57  is fixed on a protruding end portion of the balancer shaft  80 , the protruding end portion protruding from the left case half  30 . The balancer  93  rotates together with the balancer shaft  80  in a direction indicated by the arrow  94  in  FIG. 2 . In addition, a lower portion inside the cam chain chamber  57  forms a part of the second oil sump  72 , and oil is pooled in the lower portion inside the cam chain chamber  57  as indicated by the dashed line L in  FIG. 2 . Meanwhile, the balancer  93  is arranged at such a position as to be able to be partially immersed into the oil pooled in the lower portion inside the cam chain chamber  57 . With this arrangement, the oil pooled in the lower portion inside the cam chain chamber  57  is splashed by the balancer  93 . 
         [0042]    The oil pooled in the lower portion inside the cam chain chamber  57  is sucked in by the oil pump  76 . If the oil splashed by the rotation of the balancer  93  falls into the second oil sump  72 , bubbles are generated in the oil in the second oil sump  72 , in turn making air likely to be mixed into the oil which is to be sucked by the oil pump  76 . In this regard, a wall portion  95  covering the balancer  93  at least from above is provided integrally on the left case half  30  of the crankcase  25  in the engine main body  13  in such a manner as to be adjacent to the outer periphery of the balancer  93 . In Embodiment 1, the wall portion  95  is formed in an arcuate shape to cover the balancer  93  from above. 
         [0043]    Referring the examples of  FIG. 4  and  FIG. 5 , the guide supporting portion  66  recessed in the substantially “J” shape, into which the one end portion of the cam chain guide  65  is fitted to be supported, is formed integrally on the left case half  30  of the crankcase  25  at the side of the balancer  93 . The wall portion  95  is formed integrally on the left case half  30  in such a manner as to be continuously connected to the guide supporting portion  66 . 
         [0044]    Moreover, a cutout  96  is provided in the wall portion  95 . A part of oil pooled between the balancer  93  and the wall portion  95  is discharged through the cutout  96  to the side of the wall portion  95 . The cutout  96  is provided in the wall portion  95  in such a manner as to be arranged above the uppermost portion of a rotational trajectory RT of the outermost periphery of the balancer  93 . 
         [0045]    The crankcase  25  is formed by fastening the right case half  29  and the left case half  30  to each other with a plurality of bolts. At least one of these bolts, which is a bolt  98  in Embodiment 1, is inserted through a boss portion  97 . The boss portion  97  is formed integrally with the wall portion  95  in such a manner as to bulge outward from the outer periphery of the wall portion  95  at a position corresponding to the cutout  96 . A part of a large-diameter head portion  98   a  of the bolt  98  inserted through the boss portion  97  is placed to meet the cutout  96 . 
         [0046]    Referring to  FIG. 2 , a protruding portion  99  is formed integrally on the left case half  30  in order to collect the oil splashed by the drive sprocket  58 . The protruding portion  99  protrudes in a direction approaching the drive sprocket  58  at a position opposing the rotational direction  64  of the drive sprocket  58 . Moreover, in this example, a baffle plate  100  is provided integrally on a lower portion of the left case half  30  in such a manner as to be interposed between the balancer  93  and the oil strainer  75 . If the fluid level of oil pooled in the cam chain chamber  57  is lowered, oil waves would be generated by the rotation of the balancer  93 . The baffle plate  100  is designed to prevent such oil waves from reaching the oil strainer  75  side. 
         [0047]    Next, the operation of Embodiment 1 will be described. The cam chain chamber  57 , which houses the drive sprocket  58  provided on the crankshaft  14  and a part of the cam chain  59  wound around the drive sprocket  58 , is formed between the crankcase  25  and the electric-generator cover  53  in the engine main body  13 . The balancer  93 , which is rotated by the power transmitted from the crankshaft  14 , is arranged in the cam chain chamber  57  at the position where the balancer  93  can splash the oil pooled in the lower portion inside the cam chain chamber  57 . The wall portion  95 , which is adjacent to the outer periphery of the balancer  93  in such a manner as to cover the balancer  93  at least from above, which is the wall portion  95  formed in the arcuate shape to cover the balancer  93  from above in Embodiment 1, is provided integrally on the left case half  30  of the crankcase  25  in the engine main body  13  in such a way as to be adjacent to the outer periphery of the balancer  93 . 
         [0048]    With this structure, the oil splashed by the rotation of the balancer  93  is caused to hit the wall portion  95  to be collected. Accordingly, the oil falls in drops from the wall portion  95 , so that bubbles are unlikely to be generated in the oil. As a result, it is possible to make air unlikely to be mixed into the oil which is to be sucked in by the oil pump  76 . 
         [0049]    Furthermore, the cutout  96  for discharging a part of the oil pooled between the balancer  93  and the wall portion  95  to the side of the wall portion  95  is provided in the wall portion  95 . Discharging a part of the oil pooled between the balancer  93  and the wall portion  95  to the side of the wall portion  95  can reduce the rotational friction of the balancer  93 . In addition, the cutout  96  is arranged above the uppermost portion of the rotational trajectory RT of the outermost periphery of the balancer  93 . This arrangement makes it possible to prevent the oil splashed by the balancer  93  from reaching directly the cutout  96  and then coming out to the side of the wall portion  95 . 
         [0050]    The crankcase  25  is formed of the right case half  29  and the left case half  30  fastened to each other with the plurality of bolts. At least one of these bolts, which is the one bolt  98  in Embodiment 1, is arranged in such a manner as to partially meet the cutout  96 . Accordingly, the flexibility in the layout of the bolt  98  can be enhanced with the wall portion  95  not interfering with the layout of the bolt  98 . 
         [0051]    Moreover, the guide supporting portion  66  is formed integrally on the left case half  30  of the crankcase  25  at the side of the balancer  93 . The wall portion  95  is formed integrally on the left case half  30  in such a manner as to be continuously connected to the guide supporting portion  66 . Accordingly, the guide supporting portion  66  as well is provided with the function to collect the oil splashed by the balancer  93 , whereby the effect of collecting oil can be enhanced. 
         [0052]    Although the embodiment of the present invention has been described so far, the present invention is not limited to the above-described embodiment. Therefore, various modifications in design may be made without departing from the present invention described in the scope of claims. 
       EXPLANATION OF THE REFERENCE NUMERALS 
       [0000]    
       
           13  ENGINE MAIN BODY 
           14  CRANKSHAFT 
           25  CRANKCASE 
           29  RIGHT CASE HALF 
           30  LEFT CASE HALF 
           31  MATCHING INTERFACE 
           58  DRIVE SPROCKET 
           59  CAM CHAIN 
           57  CAM CHAIN CHAMBER 
           65  CAM CHAIN GUIDE 
           66  GUIDE SUPPORTING PORTION 
           93  BALANCER 
           95  WALL PORTION 
           96  CUTOUT 
           98  BOLT 
         RT ROTATIONAL TRAJECTORY