Abstract:
An outboard motor with an engine where the exposed ends of the crankshaft and camshaft project downward toward the bottom surface of the engine. An accommodation chamber is recessed within the bottom surface of the engine. A chain driven camshaft drive mechanism fits within this accommodation chamber. An oil pump, mounted below the accommodation chamber, is driven by the crankshaft. The bottom end of the crankshaft is sandwiched between the bottom surface of the engine and an oil seal housing. The oil seal housing fits within a recessed opening in a plate-like engine holder positioned below the engine. A plurality of positioning and fastening bosses are used to align and fix the oil seal housing to the engine. When the engine is removed from the outboard motor, its bottom surface is flat enabling the engine sit upright on a workbench.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an outboard motor used to propel a boat. More specifically it relates to a four-stroke engine mounted within an outboard motor. 
     In general, outboard motors have an engine mounted on a plate-like engine holder. The engine contains a vertically mounted crankshaft which is rotatably connected to the lower end of the crankshaft. The crankshaft extends downward and drives a screw propeller. Four-stroke engines are more prevalent than two-stroke engines in today&#39;s outboard motors due to environmental considerations. 
     In a four-stroke engine, a camshaft drive mechanism transmits the rotation of the crankshaft to a camshaft located above the engine. Camshaft drive mechanisms generally use a belt drive system. A drive pulley is attached to the upper end of the crankshaft which projects from the upper surface of the engine. A driven pulley is connected to the upper end of the camshaft which projects from the upper surface of the engine. A toothed belt is wrapped around the drive pulley and driven pulley. 
     The engine is lubricated with an oil pump. The oil pump is mounted at the lower surface of the engine. The oil pump is driven by either the crankshaft or camshaft. The oil is drawn up from the oil pan and distributed within the engine providing lubrication. In order to prevent oil leaks, an oil seal housing containing an oil seal is located along the lower surface of the engine where the crankshaft projects downward. 
     In conventional outboard motors, however, substantial space must be provided above the engine because the camshaft drive mechanism is located along the upper surface of the engine. This makes it difficult to fit anything else above the engine. Additionally, in such a configuration, the length of crankshaft that must be exposed is relatively long in order to accommodate the drive pulley and fly wheel. This inevitably causes rotational vibration. 
     On the other hand, if the camshaft drive mechanism is located on the lower part of the engine, the height of the engine increases and this raises the center of gravity of the outboard motor. Also, it is necessary to provide a dedicated casing member to accommodate the camshaft drive mechanism along the bottom surface of the engine. This increases the cost and weight of the outboard motor. It is also more difficult to design and layout the outboard motor engine because the oil pump and the oil seal housing must be adjacent to the camshaft drive mechanism. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to overcome the drawbacks and limitations of the prior art. 
     It is a further object of the present invention to reduce the overall height needed for the outboard motor. 
     It is yet a further object of the present invention to provide a camshaft drive mechanism, oil pump and oil seal housing along the lower surface of the engine without increasing its cost or weight. 
     It is yet a further object of the present invention to improve the design and layout of an outboard motor. 
     It is yet another object of the invention to improve the ability to attach and detach the oil seal housing while maintaining a good oil seal. 
     It is yet another object of the present invention to simplify the positioning of the oil seal housing when attaching it to the engine. 
     It is yet another object of the present invention to improve the start-up characteristics of the engine especially after it is tilted upward. 
     Briefly stated, the present invention provides an outboard motor with an engine where the exposed ends of the crankshaft and camshaft project downward toward the bottom surface of the engine. An accommodation chamber is recessed within the bottom surface of the engine. A chain driven camshaft drive mechanism fits within this accommodation chamber. An oil pump, mounted below the accommodation chamber, is driven by the crankshaft. The bottom end of the crankshaft is sandwiched between the bottom surface of the engine and an oil seal housing. The oil seal housing fits within a recessed opening in a plate-like engine holder positioned below the engine. A plurality of positioning and fastening bosses are used to align and fix the oil seal housing to the engine. When the engine is removed from the outboard motor, its bottom surface is flat enabling the engine sit upright on a workbench. 
     According to an embodiment of the invention, there is provided an outboard motor comprising: an engine; an accommodation chamber the accommodation chamber being disposed within a bottom portion of the engine; a camshaft drive mechanism; the camshaft drive mechanism being disposed within the accommodation chamber; and means for rotating the camshaft drive mechanism. 
     According to another embodiment of the invention, there is provided an engine comprising: an engine body; an accommodation chamber; the accommodation chamber being disposed within a bottom portion of the engine body; a camshaft drive mechanism; the camshaft drive mechanism being disposed fully within the accommodation chamber; and means for rotating the camshaft drive mechanism. 
     The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a left-side view showing one example of an outboard motor employing one mode of embodiment of the present invention. 
     FIG. 2 is an enlarged view showing a portion of the engine the engine holder and oil pan, and is a figure according to one embodiment of the present invention. 
     FIG. 3 is a bottom view of the engine taken along arrows III—III of FIG.  2 . 
     FIG. 4 is an enlarged view of the area IV of FIG.  2 . 
     FIG. 5 is a bottom view of the oil seal housing. 
     FIG. 6 is a longitudinal cross section of an oil seal housing along the line VI—VI of FIG.  5 . 
     FIG. 7 is a top view of an oil seal housing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, an outboard motor  1  includes an engine  2  mounted in the upper region of outboard motor  1 . Various engines can be used in such an outboard motor  1 , but in this embodiment engine  2  is a linear, three cylinder, four stroke engine. Engine  2  is fixed to a plate-like engine holder  8 . Engine  2  includes a vertically orientated crankshaft  3  disposed within a crankcase  4 . A cylinder block  5  is attached to a cylinder head  6 . A head cover  7  encloses cylinder head  6 . Engine  2  also includes an oil pan  9  mounted along its lower surface. Attached to the lower part of oil pan  9  is a drive housing  11 . A gear housing  12  is disposed below drive housing  11 . 
     Engine  2 , engine holder  8  and oil pan  9  are waterproofed by a two-part engine cover  13 . Engine cover  13  includes a lower cover  13   a  and an upper cover  13   b . Lower cover  13   a  is fixed to engine holder  8  and oil pan  9 . Upper cover  13   b  is detachably fixed to lower cover  13   a  allowing servicing. 
     A drive shaft  14  is connected to the bottom end of crankshaft  3 . Drive shaft  14  extends downward through engine holder  8 , oil pan  9  and drive housing  11  terminating in a gear housing  12 . Gear housing  12  encloses a horizontally mounted propeller shaft  15  and a screw propeller  16 . 
     A bevel gear mechanism  17  and a clutch shifter  18  couple drive shaft  14  to propeller shaft  15 . The rotation of drive shaft  14  is transmitted to propeller shaft  15  via bevel gear mechanism  17  rotating screw propeller  16 . The rotation of screw propeller  16  provides the motive force. Because drive shaft  14  rotates in only one direction, clutch shifter  18  switches the rotation of propeller shaft  15  between forward and reverse. By selecting forward or reverse, the user is able to direct the boat both forward and backward using outboard motor  1 . 
     The upper and lower ends of a swivel shaft  23  are fixed to mounts  21  and  22 . Mount  21  is attached to the front edge of engine holder  8 . Mount  22  is disposed along the front of drive housing  11 . Swivel shaft  23  is axially supported with the freedom to rotate left and right on a clamp bracket  24 . Clamp bracket  24  is fixed to the stern of a boat (not shown.) The boat is steered by turning outboard motor  1  left and right about swivel shaft  23 . Outboard motor  1  can also be tilted vertically about a tilt shaft  24   a  mounted in clamp bracket  24 . 
     Referring to FIG. 2, a camshaft  26  is axially supported and vertically orientated inside cylinder head  6 . A valve-drive mechanism (not shown) is driven by the rotation of camshaft  26 . The rotation of crankshaft  3  is stepped down by one-half and transmitted to camshaft  26  by means of a chain-drive type camshaft drive mechanism  27  disposed in the lower part of engine  2 . 
     Referring now to FIGS. 3 and 4, a drive sprocket  28  connects the lower end of crankshaft  3  projecting from the lower surface of engine  2 . A driven sprocket  29  is connected to the lower end of camshaft  26  which also projects from the lower surface of engine  2 . A timing chain  30  links drive sprocket  28  to driven sprocket  29 . The tension of timing chain  30  is adjusted using a chain tensioner  31  and a chain adjuster  32  disposed along the lower surface of engine  2 . Timing chain  30  is guided with a chain guide  33 . Note that the ratio of teeth between drive sprocket  28  and driven sprocket  29  is set at 1:2. 
     Referring to FIGS. 2 and 3, camshaft drive mechanism  27  fits within an accommodation chamber  35 . Accommodation chamber  35  is disposed within engine  2  and engine holder  8 . A recess  35   a  is formed within the lower surface of engine  2 . Camshaft drive mechanism  27  fits within accommodation chamber  35  and recess  35   a  located above an upper joining surface A of engine holder  8 . 
     When engine  2  operates, drive sprocket  28  rotates together with crankshaft  3 . Timing chain  30  drives driven sprocket  29  which turns camshaft  26 . Camshaft  26  rotates at half the speed of crankshaft  3 . The tension of timing chain  30  is regulated by chain adjuster  32  pressing on chain tensioner  31 . 
     An oil pump  37  is disposed at the bottom of camshaft  26 . Oil pump  37  is fixed to the lower surface of engine holder  8 . A fixing surface C is disposed between camshaft drive mechanism  27  and a lower joining surface B of engine holder  8 . A main shaft  38  of oil pump  37  extends upwards and is connected to the lower end of camshaft  26 . An oil intake pipe  39  extends downwards towards the floor of oil pan  9 . An oil strainer  40  is attached to the end of oil intake pipe  39 . Oil pools inside oil pan  9 . 
     Oil pump  37  is driven by the rotation of camshaft  26 . Oil pump  37  draws the pooled oil through oil intake strainer  40  and up oil intake pipe  39  lubricating engine  2 . After lubricating engine  2 , the oil naturally drains back into oil pan  9  through a plurality of oil returning holes  41 ,  42 ,  43  and  44 . 
     Referring to FIGS. 5,  6  and  7 , an oil seal housing  46  at the bottom of engine  2  is equipped with a fixing flange  47 . Fixing flange  47  is fixed to the bottom of engine  2 . A seal holder  48  centrally projects from fixing flange  47 . Fixing flange  47  is bolted to engine  2  by two bolt fasteners,  49  and  50  and a positioner  51 . A centrally located shaft hole  52  is disposed above seal holder  48 . Seal holder  48  is fitted with an oil seal  53  (see FIG. 4.) 
     Referring again to FIGS. 3 and 4, a pair of fastening bosses  55  and  56  project from the lower surface of cylinder block  5  and crankcase  4 , sandwiching crankshaft  3 . Fastening boss  55  is located inside the area bounded by timing chain  30 . A pair of positioning bosses  57  and  58  are disposed to the left and right of fastening boss  56 . 
     Fastening bosses  55  and  56  and positioning bosses  57  and  58  extend below camshaft drive mechanism  27  and timing chain  30 . The lower surfaces of fastening bosses  55  and  56  and positioning bosses  57  and  58  are used to attach oil seal housing  46 . Bolt fasteners  49  and  50  of oil seal housing  46  are matched respectively to fastening bosses  55  and  56 . Positioner  51  aligns with positioning boss  58  and a knock pin (not shown) is inserted. Bolt-fasteners  49  and  50  are attached to fastening bosses  55  and  56  with bolts  59  and  60 . This arrangement positions and secures oil seal housing  46  to engine  2 . 
     Oil seal housing  46  is lower than both camshaft drive mechanism  27  and the lower end of crankshaft  3 . A sleeve  28   a  is part of drive sprocket  28 . Sleeve  28   a  passes through seal holder  48  which passes through shaft hole  52  of oil seal housing  46 . Oil seal  53  fits within seal holder  48  and presses against the outer surface of sleeve  28   a . Other configurations could also be used such as having oil seal  53  press against the outer surface of the lower end of crankshaft  3 . 
     A housing recess  62  disposed on the upper surface of engine holder  8  surrounds oil seal housing  46 . The lower surface of seal holder  48  of oil seal housing  46  joins with an inner flat surface  63  of housing recess  62 . This joint is made liquid-tight using a packing material such as an O-ring  64 . 
     Housing recess  62  includes a cylindrical recess  65  and a shaft hole  66 . Shaft hole  66  is concentric with but smaller in diameter than cylindrical recess  65 . Shaft hole  66  aligns with a shaft chamber  67  disposed within oil pan  9  and drive housing  11  (FIG. 1.) Sleeve  28   a  of drive sprocket  28  fits within cylindrical recess  65 . Drive shaft  14  connects with sleeve  28   a  and passes through shaft hole  66  and shaft chamber  67 . An oil seal  68  fits against the inner circumference of shaft hole  66  and presses against the outer circumferential surface of drive shaft  14 . 
     The pooled oil inside oil pan  9  and the oil flowing down from engine  2  is sealed by oil seal  53  disposed in oil seal housing  46 , O-ring  64  on inner flat surface  63  of housing recess  62 , and oil seal  68  disposed within shaft hole  66 . The above combination is extremely effective at sealing the oil in and keeping the oil from leaking into cylindrical recess  65 , shaft hole  66  and shaft chamber  67 . In an outboard motor as described above, camshaft drive mechanism  27  fits within camshaft drive mechanism accommodation chamber  35  disposed within engine  2  and engine holder  8 . With this configuration, the need for a separate dedicated casing member to contain camshaft drive mechanism  27  is eliminated. This reduces the overall height and weight of engine  2 , as well as lowering production costs. 
     Camshaft drive mechanism accommodation chamber  35  includes recess  35   a  located in the lower surface of the engine  2 . Camshaft drive mechanism  27  fits within accommodating recess  35   a  and thus camshaft drive mechanism  27  is actually located above upper joining surface A of engine holder  8 . This reduces the thickness of the engine holder  8 , further lowering the overall height of engine  2 . It is to be noted that because camshaft drive mechanism  27  fits entirely within engine  2 , the bottom surface is flat. When engine  2  is removed from outboard motor  1  and placed on a work bench, it is stable and easy to work on. 
     A further reduction in height is achieved by utilizing a chain drive system camshaft drive mechanism  27 . The present invention&#39;s chain drive mechanism is thinner than conventional belt drive systems, therefore overall height is further reduced. 
     The present invention fixes oil pump  37  to engine holder  8 . This configuration reduces the overall height of engine  2  over conventional engines where the oil pump is located on the lower surface of the engine. Oil pump  37  is attached to fixing surface C. Fixing surface C is below cam shaft drive mechanism  27 , but above lower joining surface B. This allows oil pump  37  to be separate from cam shaft drive mechanism  27 . This makes it easier to lay out parts in engine  2 . It also improves the performance of oil pump  37 . Oil pump  37  is closer to oil pan  9 . This reduces the oil intake lift which improves the lubrication of engine  2 . 
     Additionally, the present invention reduces the overall height of engine  2  by locating oil seal housing  46  below camshaft drive mechanism  27  while at the same time allowing oil seal housing  46  to fit within housing recess  62  (located on the upper surface of engine holder  8 .) This configuration also allows oil seal housing  46  to be separate from camshaft drive mechanism  27  making it easier to lay out parts in engine  2 . 
     The lower surface of oil seal housing  46  is liquid-tight because O-ring  64  presses against inner flat surface  63  of housing recess  62 . This reliably seals the oil inside engine  2  side and prevents oil leaks. Also, because oil pump  37  is driven by camshaft drive mechanism  27 , oil pump  37  and oil seal housing  46  are located apart from each other. This makes it is easier to lay out parts in engine  2 . 
     Fastening bosses  55  and  56  are located in cylinder block  5  and crank case  4 , sandwiching crankshaft  3 . Bolts  59  and  60  fix oil seating housing  46  to engine  2 . Because fastening boss  55  is located within an area bounded by timing chain  30 , it remains accessible without disturbing timing chain  30 . This allows oil seal housing  46  to be attached and detached without removing timing chain  30  making maintenance easier. 
     Also, because positioning bosses  57  and  58  adjoining fastening boss  56  have a gap from fastening boss  56 , it is simpler to position oil seal housing  46 . Additionally, when outboard motor  1  is tilted up about tilt shaft  24   a  of clamp bracket  24 , oil flows between fastening boss  56  and positioning bosses  57  and  58  emptying oil seal housing  46 . Because the oil is returned to oil pan  9 , engine  2  is satisfactorily lubricated even after being tilted. This lowers mechanical losses and improves the starting ability of engine  2 . 
     Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.