Abstract:
To provide the breather structure of a shaft-drive-type drive device which can miniaturize a gear casing as a whole and can exhibit an excellent appearance. A shaft-drive-type drive device is capable of transmitting an output of an engine mounted on a vehicle body to a wheel by way of a drive shaft by connecting one end of the drive shaft to an output shaft of the engine by way of a universal joint and by connecting the wheel to another end side of the drive shaft by way of gears or the like. A breather mechanism, which performs a breathing operation of the inside of a gear casing housing the gears or the like, is mounted on the gear casing, and an atmosphere opening portion of the breather mechanism is formed to open upwardly in the vertical direction of a vehicle and inwardly in the width direction of the vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2007-086636 filed on Mar. 29, 2007 the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to the breather structure of a shaft-drive-type drive device in a shaft-drive-type power transmission mechanism for a motorcycle or the like. 
     2. Description of Background Art 
     In general, a shaft-drive-type power transmission mechanism for a motorcycle or the like is configured such that a drive bevel gear is integrally formed on a rear end of a drive shaft interlocked with an engine, and the drive bevel gear is meshed with a driven bevel gear which is pivotally supported on a rear fork and is interlocked with a rear wheel so as to transmit the rotation of the engine to the rear wheel. The drive and driven bevel gears are housed in a hermetically sealed gear chamber formed in a final casing which is mounted on one side of the rear fork. The drive and driven bevel gears are lubricated by lubricating oil sealed in the gear chamber. Further, for reducing air resistance when the drive and driven bevel gears are rotated, particularly, when the drive and driven bevel gears are rotated at a high speed, a breather mechanism for performing breathing of the gear chamber is mounted on the final casing. See, for example, JP-UM-A-58-116887 and JP-B-62-26959. 
     However, the conventional construction has a drawback wherein the breather mechanism for breathing is mounted on an upper portion of a gear box in a projecting manner. Thus, parts for forming the breather mechanism become necessary. Further, a portion of the breather mechanism projects from the box. Thus, there arises a drawback wherein the design property is lowered and the casing becomes large-sized as a whole. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     Accordingly, it is an object of an embodiment of the present invention to provide the breather structure of a shaft-drive-type drive device which can overcome the above-mentioned drawbacks of the prior art, can miniaturize a gear casing as a whole, and can exhibit an excellent appearance. 
     According to an embodiment of the present invention, in the breather structure of a shaft-drive-type drive device capable of transmitting an output of an engine mounted on a vehicle body to a wheel by way of a drive shaft by connecting one end of the drive shaft to an output shaft of the engine by way of a universal joint and by connecting a wheel to another end of the drive shaft by way of gears or the like, the breather structure includes a breather mechanism which performs a breathing operation between the inside of a gear casing which houses the gears or the like therein and an atmosphere side. In addition, an atmosphere opening portion of the breather mechanism is formed to open upwardly in the vertical direction of a vehicle and inwardly in the lateral direction of the vehicle. 
     According to an embodiment of the present invention, the breather mechanism does not project upwardly in the vertical direction of the vehicle. Thus, the gear casing can be formed in a compact shape as a whole and, at the same time, the breather mechanism is concealed inwardly in the lateral direction of the vehicle as viewed in a side view of a vehicle body. Thus, it is possible to enhance the appearance of the breather structure. 
     A water-proof moisture-permeable material may be arranged in an atmosphere opening portion of the breather mechanism. 
     The water-proof moisture-permeable material may be any material provided that the material allows air to flow into and to flow out from the gear casing but prevents water or moisture from intruding into the gear casing. 
     Further, the atmosphere opening portion of the above-mentioned breather mechanism may be formed to open in a space formed between the gear casing and a disc brake. The above-mentioned breather mechanism may be arranged on a front portion of the gear casing in the longitudinal direction of the vehicle. 
     By allowing the atmosphere opening portion to open in the space sandwiched between the gear casing and the disc brake, the disturbances (rain water or the like) do not directly impinge on the atmosphere opening portion. Thus, it is possible to prevent the intrusion of water. 
     Further, the breather mechanism may be configured such that the breather mechanism includes a breather boss portion formed on the gear casing and a ventilation hole formed in the breather boss portion, the ventilation hole is in communication with an inclined hole formed in the gear casing, and an end portion of the inclined hole penetrates a side wall of the gear casing and opens in the gear casing. Further, the end portion of the inclined hole may be in communication with a space formed between a bearing arranged in the inside of the gear casing and a sealing member. The space may be in communication with the gear case through a space formed between an outer race and an inner race of the bearing. 
     The breather mechanism includes the ventilation hole and the inclined hole which are formed in the gear casing, and the end portion of the inclined hole penetrates the side wall of the gear casing and opens in the gear casing. Thus, it is possible to realize the breather mechanism with the extremely simple construction. Further, by allowing the end portion of the inclined hole to be in communication with the space formed between the bearing and the sealing member inside the gear casing, and by allowing the space to be in communication with the gear chamber through the space formed between the outer race of the bearing and the inner race of the bearing, it is possible to efficiently release air in the gear chamber to the atmosphere. 
     According to an embodiment of the present invention, the breather mechanism does not project upwardly in the vertical direction of the vehicle different from the conventional breather mechanism. Thus, the whole gear casing can be formed in a compact shape and, at the same time, the breather mechanism can be concealed inwardly in the lateral direction of the vehicle as viewed in a side view of a vehicle body. Thus, it is possible to enhance the appearance of the breather structure. 
     Further, by arranging the water-proof moisture-permeable material in the atmosphere opening portion of the breather mechanism, air can flow into and flow out from the gear casing but water or moisture can not intrude into the inside of the gear casing. 
     By opening the atmosphere opening portion of the breather mechanism in the space sandwiched between the gear casing and the disc brake, the disturbances (rain water or the like) do not directly impinge on the atmosphere opening portion. Thus, it is possible to prevent the intrusion of water into the gear casing. 
     Further, by constructing the breather mechanism using the ventilation hole and the inclined hole formed in the gear casing, and by allowing the end portion of the inclined hole to penetrate the side wall of the gear casing and to open in the gear casing, it is possible to realize the breather mechanism with an extremely simple construction. 
     By allowing the end portion of the inclined hole to be in communication with the space defined between the bearing and the scaling member in the inside of the gear casing, and by allowing the space to be in communication with the gear chamber through the space defined between the outer race and inner race of the bearing it is possible to efficiently release air in the gear chamber to the atmosphere. 
     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 side view of a motorcycle having the breather structure of a shaft-drive-type drive device according to one embodiment of the present invention; 
         FIG. 2  is a perspective view showing a final casing; 
         FIG. 3  is a cross-sectional developed view taken along a line III-III in  FIG. 2 ; 
         FIG. 4  is a perspective view showing a state wherein a rear-fork-side casing portion and a wheel-side casing portion are fastened to each other in the final casing; 
         FIG. 5  is a perspective view of the final casing with a part broken away; 
         FIG. 6  is a longitudinal cross-sectional view of a rider&#39;s seat; and 
         FIG. 7  is a cross-sectional view taken along a line VII-VII in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, one embodiment of the present invention is explained in conjunction with attached drawings. 
       FIG. 1  is a schematic view of a motorcycle which includes the breather structure of a shaft-drive-type drive device according to one embodiment of the present invention. Here, the vertical direction and the longitudinal direction in the explanation made hereinafter indicate directions by reference to the motorcycle shown in  FIG. 1 , and the lateral direction indicate a direction as viewed from a rider. 
     As shown in  FIG. 1 , a motorcycle  1  includes a vehicle body frame  6 . The vehicle body frame  6  includes a head pipe  61 , a pair of left and right main frames  62  which extends obliquely in the rearward and downward direction from the head pipe  61 , a pair of left and right pivot plates  63  which is connected to rear portions of the main frames  62 , and a cross member not shown in drawing which connects the pivot plates  63  to each other horizontally. 
     A front fork  3  is, as shown in  FIG. 1 , connected to the head pipe  61  of the vehicle body frame  6  in a rockable manner, a front wheel  2  which includes a hydraulic disc brake is rotatably supported on a lower end portion of the front fork  3 , and a front fender  20  is arranged above the front wheel  2 . The front fender  20  is mounted in a state wherein the front fender  20  is supported on the front fork  3 . Further, a steering wheel  5  is mounted on an upper end portion of the front fork  3 . A water-cooled in-line transverse-mounted 4-cylinder engine  19  is mounted on a lower side of a center portion of the vehicle body frame  6 . Middle cowlings  8  are arranged on both left and right sides of the engine  19 . The middle cowlings  8  are detachably mounted on a vehicle body in a state that the middle cowlings  8  are contiguously formed with an upper cowling  7 . Further, a two-bulb head light  28 , a wind screen  29 , a pair of left and right front blinkers  27  and a pair of left and right rearview mirrors  30  are mounted on the upper cowling  7 . 
     A lower cowling  9  is mounted on a lower portion of the engine  19 , and the lower cowling  9  is detachably mounted on the vehicle body in a state wherein the lower cowling  9  is contiguously formed with the middle cowlings  8 . Further, a fuel tank  21  is arranged above the engine  19  and is mounted on an upper portion of the vehicle body frame  6 , and a rider&#39;s seat  22  is mounted on a rear portion of the fuel tank  21 . A half cover  24  is mounted on a front side of the fuel tank  21 , and the half cover  24  covers a space in front of the fuel tank  21  from above. A rear cowling  41  and a rear fender  42  are mounted below a rear portion of the rider&#39;s seat  22 . A stop lamp  43  and a pair of left and right rear blinkers  44  are mounted on the rear fender  42 . 
     In a rear lower portion of the vehicle body frame  6 , as shown in  FIG. 1 , a rear fork  23  is supported on the pivot plate  63  by way of a pivot shaft (not shown in the drawing) in a rockable manner, and a shaft-drive-type rear wheel  25  which includes a hydraulic disc brake  80  is rotatably supported on a rear end portion of the rear fork  23  below the rear fender  42 . Further, a bracket  46  is mounted on a center upper portion of the rear fork  23 , a lower end of a rear shock absorber  47  is connected to the bracket  46 , and an upper end of the rear shock absorber  47  is connected to a bracket (not shown in the drawings) which is mounted on the main frame  62 . The rear fork  23  also functions as a shaft casing which covers a drive shaft  71  with one end  71   a  of the drive shaft  71  being connected to an output shaft  18  of the engine  19  by way of a universal joint (universal coupling)  72  and another end  71   b  of the drive shaft  71  is connected to a drive-shaft distal end shaft  74  by way of a fastening joint  73 . The drive-shaft distal end shaft  74  is rotatably supported in the inside of a final casing (gear casing)  81  arranged on a rear portion of the rear fork  23  by way of a bearing  75 . 
       FIG. 2  is a perspective view showing the final casing  81 . The final casing  81  includes a rear-fork-side casing portion  83  which is fastened to a rear end of the rear fork  23  using a plurality of bolts  82  and a wheel-side casing portion  85  which is fastened to the rear-fork-side casing portion  83  using a plurality of hexagon socket head bolts  84  (see  FIG. 4 ). A flange  98  is integrally formed on the rear-fork-side casing portion  83 . The flange  98  is Drought into contact with a mating flange  99  which is integrally formed on a rear end of the rear fork  23 , and the respective flanges  98 ,  99  are fastened to each other using the plurality of bolts  82 . Further, in the inside of the respective casing portions  83 ,  85 , as shown in  FIG. 3 , a power transmission mechanism  86  is housed which transmits power of the engine  19  transmitted by means of the drive shaft  71  to the rear wheel  25 . In the power transmission mechanism  86 , a drive bevel gear  87  is integrally formed on a rear portion of the drive-shaft distal end shaft  74  shown on a left end in the drawing, and the drive-shaft distal end shaft  74  is rotatably supported on a bearing  75  and a bearing  76  which are positioned at both sides of the drive bevel gear  87  in the inside of the rear-fork-side casing portion  83 . The above-mentioned bearing  76  which is arranged on a deep side of the drive bevel gear  87  is supported on a bearing supporting portion  76   a  (see  FIG. 5 ) which is mounted in the inside of the rear-fork-side casing portion  83  in a projecting manner. 
     The above-mentioned drive bevel gear  87  is meshed with a driven bevel gear  88 . The driven bevel gear  88  is engaged with a spline shaft  89   a  formed on a center portion of a power transmission shaft  89  by spline fitting, and is held in place by a retainer ring  90 . The above-mentioned power transmission shaft  89  has one end portion  89   b  thereof rotatably supported on a bearing  91  arranged in the rear-fork-side casing portion  83 . A collar  92  is fitted on another end portion  89   c  of the power transmission shaft  89  and is rotatably supported on a bearing  93  which is arranged in the wheel-side casing portion  85 . Further, a rear-wheel shaft (not shown in the drawings) of the rear wheel  25  is fastened to another end portion  89   c  of the power transmission shaft  89  in a state wherein the rear wheel shaft is integrally rotatable with the power transmission shaft  89 . The bearing  91  which supports one end portion  89   b  of the power transmission shaft  89  is held by a lid body  94 . 
     Due to such a construction, power of the engine  19  which is transmitted by way of the above-mentioned drive shaft  71  is transmitted to the power transmission shaft  89  from the drive-shaft distal end shaft  74  by way of the drive bevel gear  87  and the driven bevel gear  88 . The power is further transmitted to the rear-wheel shaft of the rear wheel  25  which is connected to the power transmission shaft  89  thus driving the rear wheel  25 . 
     A gear chamber  100  which is formed in the inside of the final casing  81  and houses the drive and driven bevel gears  87 ,  88  therein is hermetically sealed. More specifically, a sealing member  95  is arranged in a through hole which is formed in the rear-fork-side casing portion  83  and through which the drive-shaft distal end shaft  74  penetrates. A sealing member  96  is arranged in a through hole which is formed in the wheel-side casing  85  through which the power transmission shaft  89  penetrates. Further, an oil filling port  83 a is formed in a right lower portion of the rear-fork-side casing  83  in the drawing with a plug  97  being arranged in the oil filling port  83   a . A proper quantity of lubricating oil is filled into the gear chamber  100  formed in the final casing  81  from the oil filling port  83 a by removing the plug  97 . 
     Next, a breather mechanism for breathing according to this embodiment is explained.  FIG. 4  is a perspective view showing a state wherein the rear-fork-side casing portion  83  and the wheel-side casing portion  85  are fastened to each other in the final casing  81 .  FIG. 5  is a perspective view of the final casing  81  with a part broken away. The final casing  81  includes, as shown in  FIG. 4 , the breather mechanism  101  for breathing which is arranged between boss portions  102 ,  102  through which the fastening bolts  84  penetrate. The breather mechanism  101  for breathing is provided for reducing air resistance when the drive and driven bevel gears  87 ,  88  (not shown in  FIG. 4 ) which are mounted in the gear chamber  100  are rotated, particularly at a high speed, and leads air in the inside of the gear chamber  100  toward the outside of the final casing  81 . The breather mechanism  101  for breathing includes a breather boss portion  104  which is mounted on an outer circumference of a front end portion of the wheel-side casing portion  85  in the longitudinal direction of a vehicle, is positioned between the boss portions  102  through which the fastening bolts  84  penetrate, and extends in a cylindrical shape while having the substantially same diameter as the boss portion  102  and a ventilation hole (atmosphere opening portion)  103  which is formed in the breather boss portion  104  and is in communication with the atmosphere. The breather boss portion  104  hardly projects to the outside in the outer radial direction of the wheel-side casing portion  85  but extends toward the rear wheel  25 , and the ventilation hole  103  opens toward a disc surface of the disc brake  80 . The breather boss portion  104  is arranged on an upper side in the vertical direction of the vehicle, and the ventilation hole  103  opens inwardly in the vehicle-width direction of the vehicle. 
     A deep end of the ventilation hole  103  is, as shown in  FIG. 5 , blind in a middle portion of the wheel-side casing portion  85  without penetrating the wheel-side casing portion  85  and is in communication with an inclined hole  105  formed in the wheel-side casing portion  85 . One end  105   a  of the inclined hole  105  opens in a blind hole  109  formed in a mating-surface- 108  side of the rear-fork-side casing portion  83  at a mating surface  108  between the wheel-side casing portion  85  and the rear-fork-side casing portion  83 . Another end  105   b  of the inclined hole  105  penetrates a side wall  106  of the wheel-side casing portion  85  and opens in the inside of the wheel-side casing  85 . Another end  105   b  of the inclined hole  105  is, as shown in  FIG. 3 , in communication with a space  110  formed between the above-mentioned bearing  93  and the sealing member  96 . The space  110  is in communication with a space  111  through a space formed between an outer race  93   a  of the bearing  93  and an inner race  93   b  of the bearing  93 , and the space  111  is in communication with the above-mentioned gear chamber  100 . 
     A water-proof moisture-permeable material  112  is arranged in an inlet portion of the ventilation hole  103 . The water-proof moisture-permeable material  112  may be any material which allows air to flow into or to flow out from the inside of the wheel-side casing portion  85  but prevents water, moisture or the like from entering the inside of the wheel-side casing portion  85 . The removal of the material  112  is prevented by a filter pusher. The arrangement position of the material  112  is not limited to the inlet of the ventilation hole  103  and the material  112  may be arranged at an arbitrary position. 
       FIG. 6  is a cross-sectional view of the rider&#39;s seat  22 .  FIG. 7  is a cross-sectional view taken along a line VII-VII in  FIG. 6 . The rider&#39;s seat  22  adopts, at a seating portion for a rider, the two-layered structure consisting of cushion members  22   a ,  22   b.  The upper-side cushion member  22   a  is formed of a single material made of foamed urethane and extends to an upper portion of the rear cowling  41  inside a skin  22   c.  Further, the lower-side cushion member  22   b  is formed of a low-repulsive mesh cushion, and is covered with a boundary layer  22   d  having rigidity. A plastic elastomer is used as a material of the cushion member  22   b , for example. 
     The rider&#39;s seat  22  adopts the two-layered structure as described above. Thus, a rider feels little fatigue even when the rider drives the motorcycle for a long time whereby riding comfort is enhanced. Further, the lower-side cushion member  22   b  is covered with the boundary layer  22   d  having rigidity and hence, the deformation of the cushion member  22   b  can be prevented. 
     In this embodiment, when the rider rides on the motorcycle and drives the engine  19 , the drive shaft  71  which is connected to the engine output shaft  18  is rotated. The rotation of the drive shaft  17  is transmitted to the rear wheel  25  by way of the drive bevel gear  87 , the driven bevel gear  88  and the power transmission shaft  89 . 
     In the above-mentioned gear chamber  100 , a breathing operation occurs due to the pressure fluctuation generated by the rotation of the drive bevel gear  87  and the driven bevel gear  88 . In this case, air in the inside of the gear chamber  100  is discharged to the space  110  through the space formed between the outer race  93   a  and the inner race  93   b  of the bearing  93  and is released to the atmosphere from the space  110  by way of the inclined hole  105  and the ventilation hole  103  which are formed in the wheel-side casing portion  85 . Accordingly, the breathing operation can be performed. 
     In this embodiment, the breather mechanism  101  does not largely project upwardly in the vertical direction of the vehicle. Thus, the final casing  81  can be formed in a compact shape as a whole. The breather boss portion  104  hardly projects to the outside of the wheel-side casing portion  85  in the outward radial direction. Thus, the breather boss portion  104  is concealed inside in the vehicle-width direction of the vehicle as viewed in a side view of the vehicle body thus enhancing design property of the motorcycle. 
     The breather boss portion  104  is arranged on an upper side in the vertical direction of the vehicle, and the ventilation hole  103  opens inwardly in the vehicle-width direction of the vehicle. Thus, water such as rain water or moisture hardly intrudes into the breather mechanism  101 . 
     Further, the water-proof moisture-permeable material  112  is arranged in the ventilation hole  103  of the breather mechanism  101 . Thus, by using the material  112 , while the breather mechanism  101  allows air to flow into or to flow out from the final casing  81 , the breather mechanism  101  can prevent water, moisture or the like from intruding into the inside of the final casing  81 . 
     The ventilation hole  103  of the breather mechanism  101  is formed to open in the space sandwiched between the final casing  81  and the disc brake  80 . Thus, disturbances such as rain water or the like hardly impinge on the atmosphere opening portion directly whereby it is possible to prevent the intrusion of water into the final casing  81 . 
     The above-mentioned breather mechanism  101  is simply configured such that the ventilation hole  103  is formed in the breather boss portion  104  formed on the wheel-side casing portion  85 , the ventilation hole  103  is in communication with the inclined hole  105  formed in the wheel-side casing portion  85 , and the inclined hole  105  opens in the wheel-side casing portion  85 . Due to such a construction, it is possible to extremely easily realize the breather mechanism  101 . 
     Further, the end portion of the inclined hole  105  is in communication with the space formed between the bearing  93  and the sealing member  96  inside the wheel-side casing portion  85  and, at the same time, the space is in communication with the space  110  through the space formed between the outer race  93   a  and the inner race  93   b  of the bearing  93 . Due to such a construction, air is released to the atmosphere from the space  110  by way of the inclined hole  105  and the ventilation hole  103  formed in the wheel-side casing portion  85 . Thus, it is possible to extremely easily realize the breather mechanism  101 . 
     Although the best mode for carrying out the present invention has been explained heretofore, the present invention is not limited to the above-mentioned embodiment and various modifications and changes are conceivable based on the technical concept of the present invention. For example, the ventilation hole  103  may open on a rear-wheel- 25  side. It is not always necessary to form the ventilation hole  103  in the cylindrical breather boss portion  104 . Further, the shape, the number and the like of the breather boss portions  104  may be respectively arbitrarily changed. 
     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.