Abstract:
An outboard motor includes a transmission device disposed on a middle portion of a drive shaft driven by an engine. The transmission device includes a forward-reverse switching device housed in a transmission case. Lubricating oil for lubricating the forward-reverse switching device is stored in the transmission case. The transmission case has a drain hole arranged to discharge lubricating oil in the transmission case that is provided in a lower portion of a side wall and in a position in front of the drive shaft, and a drain bolt for opening or closing the drain hole. An exposed opening for exposing the drain hole is provided in an upper case that covers the transmission case. As a result, work efficiency in discharging or draining of lubricating oil is greatly improved without requiring dismantling of a main body of the outboard motor.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an outboard motor, in particular, an outboard motor with an improved drain construction for lubricating oil. 
         [0003]    2. Description of the Related Art 
         [0004]    Conventionally, an outboard motor disclosed in WO 2007-007707 A1 includes a power transmission system provided on a middle portion of a drive shaft to transmit power of an engine to a propeller. The power transmission system has a speed changer constructed with a planetary gear mechanism. 
         [0005]    Accordingly, the speed of power from the engine is changed by the speed changer, and the power is transmitted to the propeller. Thereby, the propeller rotates at a prescribed speed. 
         [0006]    However, in such a conventional outboard motor, the speed changer and so forth of the power transmission system requires lubrication with lubricating oil. Further, the lubricating oil is required to be changed. 
       SUMMARY OF THE INVENTION 
       [0007]    In view of the problems described above, preferred embodiments of the present invention provide an outboard motor having a structure that enables greatly improved work efficiency in discharging or draining lubricating oil without requiring dismantling of a main body of the outboard motor. 
         [0008]    A preferred embodiment of the present invention provides an outboard motor including an engine provided in an upper portion, a drive shaft driven by the engine and arranged in a vertical direction, and a transmission device disposed on a middle portion of the drive shaft, wherein the transmission device has an automatic transmission system housed in a transmission case, a drain hole arranged to discharge lubricating oil provided in a lower portion of a side wall of the transmission case and in a position in front of the drive shaft, and an opening/closing member arranged to open or close the drain hole. 
         [0009]    The transmission case is preferably disposed in an upper case, and an exposed opening is preferably arranged to face the drain hole in the upper case. 
         [0010]    A guide member is preferably arranged to guide the lubricating oil discharged from the drain hole to the outside of the exposed opening. 
         [0011]    The drain hole is preferably disposed below a steering shaft. 
         [0012]    The drain hole is preferably covered by a cover detachably mounted on the outside of the upper case. 
         [0013]    An oil pan of the transmission device preferably has the drain hole arranged to discharge lubricating oil in the oil pan provided in the lower portion of the side wall and in the position in front of the drive shaft and the opening/closing member. When lubricating oil is discharged from the oil pan when changing the oil, the outboard motor is tilted up, the opening/closing member is removed, and the lubricating oil can easily be discharged through the drain hole without requiring dismantling of the main body of the outboard motor. This allows an improvement in the work efficiency. 
         [0014]    The transmission case is preferably disposed in the upper case, and the exposed opening is preferably provided in the upper case to face the drain hole. Therefore, lubricating oil can be discharged outside of the upper case from the drain hole via the exposed opening. 
         [0015]    The guide member is preferably arranged to guide lubricating oil discharged from the drain hole to the outside of the exposed opening. Therefore, lubricating oil does not leak in a section between the oil pan and the upper case and can be certainly discharged to the outside of the upper case. 
         [0016]    The drain hole is preferably disposed below the steering shaft. Therefore, the drain hole is not interfered with by the steering shaft and the like. This facilitates discharging of the lubricating oil. 
         [0017]    The drain hole is preferably covered by the cover detachably mounted on the outside of the upper case. Therefore, the drain hole and the opening/closing member are not exposed to the outside in a normal state (a state in which the cover is put on). This ensures an appealing external appearance. 
         [0018]    Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a side view of an outboard motor in accordance with a preferred embodiment of the present invention. 
           [0020]      FIG. 2  is a cross-sectional view of the outboard motor in accordance with a preferred embodiment of the present invention. 
           [0021]      FIG. 3  is a cross-sectional view of the outboard motor in accordance with a preferred embodiment of the present invention showing elements thereof on a larger scale. 
           [0022]      FIG. 4  is a front view of a transmission device in accordance with a preferred embodiment of the present invention. 
           [0023]      FIG. 5  is a plan view along line V-V of  FIG. 4  in accordance with a preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    Preferred embodiments of the present invention will be described hereinafter. 
         [0025]      FIGS. 1 through 5  show a preferred embodiment of the present invention. 
         [0026]    First, a construction of the outboard motor will be described. An outboard motor  11  in accordance with a preferred embodiment is mounted on a transom of a hull (not shown). 
         [0027]    The outboard motor  11  has a clamp bracket  12  fixed to the transom. A swivel bracket  14  is connected to the clamp bracket  12  via a swivel shaft  13  in the horizontal direction and a locking mechanism (not shown). A steering bracket  16  is connected to the swivel bracket  14  via a steering shaft  15  generally in the vertical direction. 
         [0028]    The outboard motor  11  is supported by the steering bracket  16 . The outboard motor  11  can be steered to the right and the left about the steering shaft  15 , and can be tilted up above the water surface by vertically turning the swivel shaft  13 . 
         [0029]    In the outboard motor  11 , a lower case  20  is provided below an upper case  19 . A substantially flat mounting plate  21  is provided in an upper portion of the upper case  19 . An engine  22  installed via the substantially flat mounting plate  21 . The engine  22  is, for example, a V6 water-cooled engine, and is placed on the mounting plate  21  with a vertically-arranged crankshaft  23 . 
         [0030]    The upper case  19  preferably has a horizontally split construction, for example, in which an upper case section and a lower case section are fastened together by a plurality of fixing bolts or other fastening members, for example. The mounting plate  21  is fixed to an upper surface of the upper case section by a plurality of fixing bolts and through bolts or other fastening members, for example. 
         [0031]    The engine  22  is covered by a detachable upper cover  24  and a lower cover  25 . The right and left side surfaces of the upper case  19  are covered by a detachable side cover  26 . 
         [0032]    A vertical drive shaft  27  is pivotally supported in the upper case  19 . An upper end of the drive shaft  27  is coupled to a lower end of the crankshaft  23  of the engine  22  preferably by spline-fitting, for example. 
         [0033]    The drive shaft  27  preferably includes a plurality of coaxially-disposed shafts, extends downward in the upper case  19 , and extends into the inside of the lower case  20 . The drive shaft  27  is coupled to a propeller shaft  29  horizontally and pivotally supported in the lower case  20  via a bevel gear mechanism  28 , thereby transmitting power. 
         [0034]    The propeller shaft  29  is preferably a double rotating shaft in which an outer shaft  29   a  and an inner shaft  29   b  are coaxially combined. In the bevel gear mechanism  28 , a drive bevel gear  28   a  unitarily rotates with the drive shaft  27 , a driven bevel gear  28   b  unitarily rotates with the outer shaft  29   a , and a driven bevel gear  28   c  unitarily rotates with the inner shaft  29   b.    
         [0035]    A first propeller  31   a  is fixed to the outer shaft  29   a . A second propeller  31   b  is fixed to the inner shaft  29   b . These members define a contra-rotating propeller mechanism  32 . An exhaust path  33  is preferably located within the axial portions of the first propeller  31   a  and the second propeller  31   b.    
         [0036]    A transmission device  36  is provided in the upper case  19 . The transmission device  36  is preferably pivotally installed in a middle portion of the drive shaft  27 . A transmission planetary gear mechanism  38 , as an example of an automatic transmission system, and a forward-reverse switching device  39  are housed in a transmission case  37  that defines a contour of the transmission device  36 . Description will not be made about a detailed construction of the forward-reverse switching device  39  and so forth. A final speed reducer  40  including a planetary gear mechanism is provided below the transmission device  36  (see  FIG. 1  and so forth). 
         [0037]    Lubricating oil is preferably stored in an oil pan  37   d  in the transmission case  37 . The lubricating oil lubricates gears, a clutch, and so forth of the forward-reverse switching device  39 . As shown in  FIG. 5 , a lubricating oil dropping path  37   e , a lubricating oil drawing path  37   f , and a coolant path  37   g  are provided in the transmission case  37 . 
         [0038]    As shown in  FIGS. 2 and 3 , the transmission case  37  has a drain hole  37   a  arranged to discharge lubricating oil in the transmission case  37  provided in a lower portion of a side wall and in a position in front of the drive shaft  27 , and a drain bolt  41  as an “opening/closing member” that is arranged to open or close the drain hole  37   a.    
         [0039]    The drain hole  37   a  is preferably formed in a boss  37   b  protruding from the transmission case  37 . A female thread  37   c  is preferably provided in an inside wall of the boss  37   b . An external thread  41   a  of the drain bolt  41  is screwed into the female thread  37   c.    
         [0040]    As shown in  FIG. 5 , the drain hole  37   a  and so forth are not positioned on an extension line L in a fore-and-aft direction of the watercraft passing through the center of the transmission case  37 , but are disposed in a position offset to the right or left by a small angle θ (for example, about 30° through about 45°). The lubricating oil drawing path  37   f  is arranged on the opposite side across the extension line L with respect to the position that the drain bolt  41  and so forth are disposed. 
         [0041]    The transmission case  37  is preferably fastened by fastening bolts via four fastening bolt holes  37   j ,  37   j  and  37   k ,  37   k , for example, as shown in  FIG. 5 . An interval between the two fastening bolt holes  37   k ,  37   k  on the front side is wider than an interval between the fastening bolt holes  37   j ,  37   j  on the rear side, thereby preventing the transmission case  37  from protruding forward and occupying a space in which the drain hole  37   a  is provided. Such a construction allows a reduction in the amount that the drain bolt  41  protrudes forward. 
         [0042]    Further, as shown in  FIG. 5 , a hydraulic path  37   m  for operating a hydraulic clutch is provided in the transmission case  37 . Hydraulic pressure is supplied to the hydraulic clutch through a solenoid valve from the hydraulic path  37   m.    
         [0043]    An exposed opening  19   a  is arranged to face the drain hole  37   a  in the upper case  19  covering the transmission case  37 . The exposed opening  19   a  preferably has a circular or substantially circular shape, and preferably has a diameter that is larger than a diameter of the boss  37   b.    
         [0044]    Further, a guide member  44  is arranged to guide lubricating oil discharged from the drain hole  37   a  to the outside of the exposed opening  19   a.    
         [0045]    The guide member  44  is preferably formed of rubber and provided with a cylinder  44   a  and a flange  44   b  formed around the cylinder  44   a . The cylinder  44   a  is fitted around the boss  37   b  and in to the exposed opening  19   a  of the upper case  19 . An end of the cylinder  44   a  is preferably tapered, and protrudes outside from the upper case  19  for a given amount. 
         [0046]    The flange  44   b  is fitted into a recess  19   b  formed in a periphery of the exposed opening  19   a  of the upper case  19 . The flange  44   b  is pressed against the recess  19   b  by a pressing plate  45 , thereby ensuring a good seal. 
         [0047]    The drain hole  37   a  and so forth are disposed below the steering shaft  15 . 
         [0048]    The drain hole  37   a  and so forth are covered by a covering  26   a  of the side cover  26  detachably mounted on the outside of the upper case  19 . 
         [0049]    When the engine  22  starts, rotation of the crankshaft  23  is transmitted to the drive shaft  27 . The rotational speed of the drive shaft  27  is changed in the transmission device  36 , and the rotational direction thereof is switched into the forward or reverse direction. Further, the rotational speed is reduced by the final speed reducer  40  and transmitted to the propeller shaft  29 . The outer shaft  29   a  of the propeller shaft  29  with the first propeller  31   a  and the inner shaft  29   b  of the propeller shaft  29  with the second propeller  31   b  rotate in opposite directions to generate a high propulsive force. 
         [0050]    In such an outboard motor, in the case of changing lubricating oil, the side cover  26  is detached, and the outboard motor  11  is turned (tilted up) to a prescribed angle about the swivel shaft  13 , thereby causing the outboard motor  11  to be in a leaning or tilting position. 
         [0051]    In this position, a lubricating oil inlet provided in an upper portion of the transmission case  37  is opened, the drain bolt  41  is removed, and the drain hole  37   a  is opened. The drain hole  37   a  is positioned in the lower portion of the side wall of the transmission case  37  and in front of the drive shaft  27 . Therefore, the drain hole  37   a  is positioned the lowest in the transmission case  37  when the outboard motor  11  is tilted up. 
         [0052]    Accordingly, the drain bolt  41  is removed when the outboard motor  11  is tilted up to facilitate discharge of lubricating oil. At the time of discharge, lubricating oil is guided by the guide member  44  to the outside of the upper case  19  and discharged. Therefore, lubricating oil does not leak in a section between the transmission case  37  and the upper case  19 . 
         [0053]    Further, the flange  44   b  and so forth of the guide member  44  reliably seals a section between the guide member  44  and the periphery of the exposed opening  19   a  of the upper case  19 . Therefore, seawater and so forth do not enter the section between the transmission case  37  and the upper case  19  through the exposed opening  19   a.    
         [0054]    Further, the drain hole  37   a  and so forth are disposed in front of the drive shaft  27  and thus are positioned adjacent to the steering shaft  15 . However, the drain hole  37   a  and so forth are not interfered with by the steering shaft  15  when the drain bolt  41  is attached and detached since the drain hole  37   a  and so forth are disposed below the steering shaft  15 . This facilitates the attaching and detaching operation. 
         [0055]    In addition, the drain hole  37   a  and so forth are covered by the covering  26   a  of the side cover  26  in a normal state. This ensures a an appealing external appearance and prevents damage to the guide member  44  and so forth. 
         [0056]    The drain hole  37   a  is offset by the angle θ, thereby preventing an increase in the amount that the drain bolt  41  protrudes forward. Accordingly, the outboard motor  11  can be disposed as close to the watercraft as possible when the transmission device  36  is provided on the drive shaft  27 . Therefore, the center of gravity of the outboard motor  11  is positioned closer to the watercraft. This reduces a load on a support member of the outboard motor  11 . The angle θ is preferably set to an angle position close to the maximum steering angle (for example, about ±32° from the center), thereby allowing discharge of the lubricating oil in a state in which the outboard motor  11  is tilted up and maintained at the maximum steering angle. This improves the work efficiency. 
         [0057]    In the above-described preferred embodiments, the transmission device  36  is preferably capable of both speed change and direction switching. However, the present invention is not limited to this case, and the transmission device  36  may only be capable of either of the above functions. 
         [0058]    While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.