Patent Publication Number: US-6213826-B1

Title: Outboard motor, and engine thereof

Description:
This application is a div. of Ser. No. 09-361,611 filed Jul. 27, 1999 now U.S. Pat. No. 6,079,384 which is a div of Ser. No. 08/932,171 filed Sep. 17, 1997 now U.S. Pat. No. 5,964,197 which is a con of Ser. No. 08-344,648 filed Nov. 18, 1994 now aband. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an outboard motor detachably mounted at a stern for use to propel a boat or ship, as well as an engine mounted in the outboard motor. The engine according to the present invention can be utilized not only as an engine for the outboard motor, but also as a general-purpose engine. 
     2. Description of the Related Art 
     In a common type of the outboard motor of the related art, an engine (a vertical engine) having a flywheel provided at an upper end of a vertically directed crankshaft protruding from an engine block is mounted in an outboard motor body case which is mounted to a boat body through an antivibration mount. Such types of the outboard motors are disclosed, for example, In Japanese Patent Application Laid-open Nos.191610/87, 192917/88 and 192918/88. 
     In these outboard motors, a ring gear is mounted around an outer periphery of the flywheel, and a starter motor is mounted above a side of the engine and meshed with the ring gear. A driving pulley of a valve-operating belt drive transmission is provided at an end of the crankshaft adjacent below the flywheel. 
     Typically, an ignition power source coil and a charging power source coil are accommodated in the flywheel to form a dynamo and hence, the flywheel has a downwardly-turned bowl-like shape. 
     In such a prior art outboard motor, the heavy flywheel having a large inertial moment, which largely influences the determination of the gravity of the position of the center of engine, is spaced farther upwardly from the antivibration mount. The crankshaft end opposite from the flywheel is coupled to a driving shaft for transmitting a driving force to a propeller. Therefore, torsional vibrational effects exert a great influence on the selection of the antivibration mount and hence, the selection of the antivibration mount must be taken into special consideration. 
     In addition, not only the flywheel but also a starter must be mounted above the engine. Therefore, the position of the center of gravity of the engine is high, which increases the moment required during tilting-up of the outboard motor, and also limits the freedom of the disposition of other auxiliaries, especially, in the case of a multi-cylinder engine the disposition of an electrical equipment box for accommodating a CDI unit plurality of coils, other auxiliaries such as and intake system auxiliaries or the like. 
     Further, in a 4-cycle engine used in the outboard motor, the driving Pulley of the wrapping type transmission is provided as a valve operating device at the crankshaft end adjacent the flywheel. The crankshaft end however requires a large diameter for mounting the flywheel. Therefore, the diameter of the driving pulley must be increased and as a result, a driven pulley adjacent a camshaft also increased in size and has a shape occupying an area near an upper portion of a cylinder head, bringing about an increase in size of an upper portion of a rear end of an engine cover spaced from a tilting shaft. However, this portion of the engine cover is liable to interfere with a boat body structure, when the outboard motor is turned upwardly about the tilting shaft and hence, the unnecessary increase in size of this portion is undesirable and inconvenient even in respect of a moment required for the turning of the outboard motor. 
     A lower portion of the outboard motor body case is formed to be narrow in order to reduce the underwater resistance of a submerged portion of the case to the utmost and to provide a reduction in weight. Therefore, an engine having a good mountability to such outboard motor body case is desired. 
     In Japanese Utility Model Application Laid-open Nos.21509/91 and 23609/91, there has been proposed an engine in which a crankshaft is oriented vertically and a flywheel is provided at a lower end of the crankshaft protruding from an engine block. Such an engine includes a transmission connected to that lower end of the crankshaft which is provided with the flywheel. Thus, this engine cannot be applied directly as an engine for use in the outboard motor, and such prior art devices not suggest any means capable of solving problems inherent in the engine of the above-described type for use in the outboard motor. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a first object of the present invention to provide an outboard motor a low center of gravity, which is easy to tilt up and is less susceptible to torsional vibration. 
     It is a second object of the present invention to provide an engine which is excellent in mountability to the outboard motor body case. 
     To achieve the first object, according to the present invention, there is provided an outboard motor comprising an engine mounted at an upper portion of an outboard motor body case which is swingable about a tilting shaft, with a crankshaft of the engine being directed in a vertical direction, wherein the crankshaft is provided, with a flywheel, at a lower end thereof which protrudes downwardly from an engine body of the engine. 
     With the above construction, since the flywheel is provided at the lower end of the crankshaft, i.e., at a lower portion of the engine, the position of the center of gravity of the engine is lowered, so that a moment required for swinging the outboard motor upwardly (i.e., tilted up) about the tilting shaft is reduced. Therefore, the effort required of a person when the outboard motor is manually tilted up is reduced. Even when the outboard motor is tilted up by a tilting device such as a hydraulic device or the like, a prompt tilting-up operation can be achieved by a relatively small-sized tilting device. In addition, the flywheel is provided at the lower portion of the engine and moreover, can be accommodated by utilizing a space between a connecting member for supporting the outboard motor body case and the engine body. Therefore, the entire height of the outboard motor is relatively low. Further, the flywheel does not exist above a driving pulley of a valve operating device provided at an upper portion of the engine and therefore, even if the driving pulley is of a sufficiently small diameter, there is no problem for handling the pulley. Consequently, a driven pulley can also be of a small diameter (in a 4-cycle engine, the diameter of a driven pulley is twice the diameter of a driving pulley) and thus, it is possible to reduce the size of the engine and outboard motor because the height can also be lowered. Yet further, a driving force is derived from a crankshaft end on the same side as the flywheel and therefore, it is possible to reduce the torsional vibration of the crankshaft. 
     To achieve the second object, according to the present invention, there is provided an engine with a crankshaft directed vertically, comprising a flywheel provided at that lower end of the crankshaft which protrudes from an engine block, and an engine mount case coupled to a lower surface of the engine block for mounting the engine, the engine mount case having a peripheral wall which extends below the flywheel to surround at least a portion of the periphery of the flywheel. 
     With the above construction, notwithstanding the flywheel being provided at the lower portion of the engine, the engine can be easily placed in position through the engine mount case. Particularly, the engine is suitable for use in the outboard motor and can be easily and satisfactorily mounted to the outboard motor body case through the engine mount case. 
     The above and other objects, features and advantages of the invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 to  12  illustrate a first embodiment of the present invention, wherein 
     FIG. 1 is a side view of the entire outboard motor; 
     FIG. 2 is a right side view of an engine; 
     FIG. 3 is a left side view of the engine; 
     FIG. 4 is a cross-sectional view of the engine; 
     FIG. 5 is a diagram illustrating a fuel supply system; 
     FIG. 6 is a view of an end of an engine block on the side of a cylinder head; 
     FIG. 7 is a vertical sectional view taken along various sections of the engine including an axis of a crankshaft; 
     FIG. 8 is an enlarged view of a portion shown in FIG. 7; 
     FIG. 9 is a top view of an engine mount case; 
     FIG. 10 is a bottom view of the engine mount case; 
     FIG. 11 is a sectional view taken along a line  11 — 11  in FIG. 7; and 
     FIG. 12 is a view of an end of the cylinder head on the side of a cylinder head cover; 
     FIGS. 13 to  19  illustrate a second embodiment of the present invention, wherein 
     FIG. 13 is a side view of the entire outboard motor; 
     FIG. 14 is a vertical sectional side view of an engine; 
     FIG. 15 is a side view of the inside of an engine room taken along a vertical section of a cover member for covering the engine; 
     FIG. 16 is a sectional view taken substantially along a line  16 — 16  in FIG. 15; 
     FIG. 17 is a schematic plan view illustrating the arrangement of the engine and auxiliaries within the engine room; 
     FIG. 18 is a centrally vertical sectional view of an upper portion of an engine cover; and 
     FIG. 19 is a sideways vertical sectional view of the upper portion of the engine cover. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will be first described with reference to FIGS. 1 to  12 . 
     FIG. 1 is a side view of the entire outboard motor to which the present invention is applied. An outboard motor body  1  is mounted at a stern  3  through a mounting means  2 . 
     The outboard motor body  1  includes an outboard motor body casing  6  which comprises an engine mount case  4  and an extension case  5 . An engine  7  is mounted on an upper portion of the outboard motor body casing  6  and covered at its upper portion with an engine cover  8 . The open air is introduced into the cover  8  through an air intake port  8   a.    
     The engine  7  will be described hereinafter. A crankshaft  9  of the engine  7  is directed vertically, and a driving shaft  10  is connected to the crankshaft  9  and extends downwardly within the outboard motor body casing  6 . The driving shaft  10  is connected at its lower end to a propeller shaft  12  through a forward and backward movement changing device  11 . A propeller  13  is rotatively driven by an engine power transmitted thereto through the crankshaft  9 , the driving shaft  10 , the forward and backward movement changing device  11  and the Propeller shaft  12 . 
     The mounting means  2  includes a bracket  15  fixed to the stern through a bolts  14 , and a swivel case  17  pivotally mounted on the, bracket  15  for vertically swinging movement through a tilting shaft  16  provided at a front end of the bracket  15  to extend transversely. A swivel shaft  18  is rotatably carried in the swivel case  17  in a vertically directed manner. The outboard motor body casing  6  is connected to the swivel shaft  18  through upper and lower connecting members  19  and  19   a . Thus, the outboard motor body casing  6 , i.e ., the outboard motor body  1 , is vertically swingable about the tilting shaft  16  and turnable in counterclockwise and clockwise directions about an axis of the swivel shaft  18 . 
     FIG. 2 is a right side view of the engine  7 ; FIG. 3 is a left side view, and FIG. 4 is a cross-sectional view. The terms “left” and “right” mean left and right when the outboard motor mounted at the stern  3  is viewed forwardly from rear (rightwardly from left in FIG.  1 ). 
     An engine body of the engine  7  includes an engine block  20 , a cylinder head  21  and a cylinder head cover  22 . The engine block  20  is constructed by integrally coupling a cylinder block portion  20   a  integrally provided with a skirt forming a half of a crankcase, with the remaining crankcase portion  20   b  by a bolt  23 . Two sets of upper and lower pairs of cylinders  24 ,  24  arranged into a laterally V-shaped configuration are disposed within the engine block  20 . More specifically, the engine  7  is a V-type 4-cycle engine with pistons  25  connected to the single crankshaft  9  directed vertically through connecting rods  26 . 
     FIG. 6 is a side view of the engine block  20  on the side of the cylinder head  21 . As can be seen from FIG. 6, the cylinders  24  are four cylinders: a pair of cylinders  24   a  and  24   b  vertically arranged on the left side, and another pair of cylinders  24   c  and  24   d  vertically arranged on the right side. These cylinders are arranged in a zigzag manner such that the left cylinders  24   a  and  24   b  are higher in level than the right cylinders  24   c  and  24   d . Such arrangement of the cylinders makes it possible to reduce the lateral width of the engine block, as compared with another V-type engine and to reduce the size of the engine  7 . 
     Intake ports  28  are provided in the cylinder head  21  in correspondence to the cylinders  24 , as shown in FIG. 4 with regard to the left (left in the outboard motor, i.e., lower as viewed in FIG. 4) cylinder  24 . The intake ports  28  are connected to the corresponding cylinders  24  through intake valves  29  and open into a side surface of the cylinder head  21 . Intake pipes  30  are connected to such openings of the intake ports  28 , respectively and extend along the side surface of the engine block  20  toward a crank chamber provided ahead. The intake pipes  30   c  and  30   d  shown in FIG. 2 are those corresponding to the cylinders  24   c  and  24   d  shown in FIG.  6  and the intake pipes  30   a  and  30   b  shown in FIG. 3 are those corresponding to the cylinders  24   a  and  24   b  shown in FIG.  6 . 
     Surge tanks  31 L and  31 R are provided on the laterally opposite sides of a front portion of the engine block  20 , and the intake pipes  30   a  and  30   b  are in communication with the surge tank  31 L, while the intake pipes  30   c  and  30   d  are in communication with the surge tank  31 R. On the other hand, a throttle body  32  having a throttle valve therein is disposed on a front and central portion of the engine block  20 , and is in communication with the surge tanks  31 L and  31 R through an air passage  33  which diverges laterally from the throttle body  32 . Air is introduced from above into the throttle body  32  via an air introducing pipe  34 . 
     The air introduced from above via the air introducing pipe  34  is adjusted in flow rate within the throttle body  32  and then distributed into the left and right surge tanks  31 . From the tanks  31 , the air is supplied as combustion air through the intake pipes  30  into the corresponding cylinders  24 , wherein fuel is injected from a fuel injection valve  35  and mixed with to such air in the intake ports  28  (FIG.  4 ). In FIG. 2, reference character  32   a  is a throttle valve stem; reference character  32   b  is a link member; and reference character  32   c  is a fastener of a rubber or the like. In FIG. 3, reference character  32   d  is a throttle valve opening degree sensor, and reference character  33   b  is an intake air temperature sensor. 
     The surge tank  31  has a connection  33   a  to the air passage  33  on a side thereof, and has a capacity area extending vertically i.e., upwardly and downwardly of the connection  33   a . The volume of the capacity area is set as required, but a portion of the capacity area lying below the connection  33   a  is located out of a flow of air from the connection  33   a  to a connection with each intake pipe  30 . Hence, should water enter an intake system, such portion also acts as a separating chamber. Reference character  93  is a drain bolt. 
     FIG. 5 is a diagram illustrating a fuel supply system. Reference character  37  is a fuel receiving pipe mounted in the outboard motor, and reference character  38  is a fuel delivering pipe mounted on a boat. By connecting these pipes  37  and  38 , the fuel can be supplied from a fuel tank  39  mounted on the boat. Reference character  40  is a low-pressure filter, and reference character  41  is a low-pressure pump. The fuel pumped from the fuel tank  39  by the low-pressure pump  41  is once stored in a gas-liquid separator  42  and then supplied via a strainer  43 , a high-pressure pump  44  and a high-pressure filter  45  to the fuel injection valve  35 . These devices and pipes mounted on the outboard motor are disposed on the left side of the engine, as shown in FIG.  3 . The high-pressure pump  44  may be disposed within the gas-liquid separator  42 . 
     An exhaust valve  46  is mounted below the intake valve  29  in each of the cylinders  24  (see FIG.  4 ), and an exhaust passage  47  is defined in the cylinder head  21  to lead to each of the exhaust valves  46 . The exhaust passages  47  extend vertically through a widthwise central portion of the cylinder head  21 , i.e., through an intermediate section between the array of the left cylinders  24   a  and  24   b  and the array of the right cylinders  24   c  and  24   d  to meet together at lower ends and open into the lower surface of the cylinder head  21  (see FIGS.  7  and  12 ). A valve operating mechanism comprising a cam  89   a  and a rocker arm  90   a  for the intake valves  29 , and a cam  89   b  and a rocker arm  90   b  for the exhaust valves  46  is shown in FIG. 12 only for the cylinders  2   a  and  24   d , but of course, a similar valve operating mechanism is mounted for each of the other cylinders. 
     As shown in FIG. 2, a starter motor  48  is mounted on the right side of the engine block  20  with its output shaft  49  protruding downwardly. A driving gear  50  is mounted to the output shaft  49  and meshed with a ring gear which is integrally formed around an outer periphery of a flywheel which will be described hereinafter. 
     FIG. 7 is a view of the engine  7  taken in various vertical sections including an axis of the crankshaft  9 , with a section of the cylinder  24   c  and a portion of a section of the cylinder  24   b  being shown. 
     The crankshaft  9  is directed vertically, as described above, and a camshaft  51  is disposed in the cylinder head  21  in parallel to the crankshaft  9 . Upper ends of the crankshaft  9  and the camshaft  51  are passed through the engine block  20  and the cylinder head  21 , respectively to project upwardly. Pulleys  52  and  53  are fixedly mounted at these upper ends. A belt  54  is wound around the pulleys  52  and  53 . Thus, the camshaft  51  is driven by the crankshaft  9  through the belt  54 . Since the engine  7  is a 4-cycle engine, the diameter of the pulley  53  is twice the diameter of the pulley  52  in order to set the rotational ratio of the crankshaft  9  to the camshaft  51  at 2:1. Reference characters  52   a  and  53   a  are controlling pick-up plates. 
     A lower surface of the engine block is formed into an open portion  55 , and a lower wall of the engine block  20  is formed by a closing plate  56  for sealingly closing the open portion  55 . The closing plate  56  is detachably secured to the engine block  20  by bolts  57  (FIGS.  2  and  3 ). A lower end of the crankshaft  9  is rotatably passed through to project downwardly, and a flywheel  58  is secured to such lower end. 
     FIG. 8 is an enlarged view of a portion in the vicinity of the flywheel  58  shown in FIG.  7 . An axial bore  59  is provided in the lower end of the crankshaft  9 , and a collar member  60  is fitted in the bore  59 . A circumferentially projecting annular flange  60   a  is formed at a lower end of the collar member  60 . The flywheel  58  is secured to the crankshaft  9  by fitting a circular bore centrally provided in a bottom plate Portion  58   a  thereof over the collar member  60  and sandwiching their peripheral portions between a lower end face of the crankshaft  9  and the flange  60   a  to clamp them together by a bolt  61 . The collar member  60  is also integrally fixedly secured to the crankshaft  9  by the bolt  61 . 
     The flywheel  58  has a peripheral wall  58   b  projecting upwardly along an outer peripheral edge of the bottom plate portion  58   a  and is formed into a dish-like shape as a whole. A dynamo  64  is mounted within a space surrounded by the peripheral wall  58   b  and includes a rotor  62  fixed to the flywheel  58  and a starter  63  fixed to the closing plate  56 . 
     Further, a ring gear  65  is integrally formed around an outer periphery of the peripheral wall  58   b  of the flywheel  58  by shrink-fitting of a gear portion or by another means. The ring gear  65  is meshed with the driving gear  50  provided on the output shaft  49  of the starter motor  48  (FIG.  2 ), and at the start of the engine, the crankshaft  9  is driven by the starter motor  48 . 
     The engine mount case  4  is coupled to the lower surface of the engine block  20  along with the closing plate  56  interposed therebetween by clamping thereof using bolts  57 . (In FIG. 7, reference character  91  is a shift rod, and reference character  92  is a shift rod operating member connected to the shift rod through a link system not shown, and FIG. 8 is another sectional view of these portions and the bolt  57  is shown.) The engine mount case  4  extends further rearwardly up to the vicinity of the cylinder head, and is also connected to the lower surface of the cylinder head  21  into which the exhaust passage  47  opens. FIG. 9 is a top view of the engine mount case  4 , wherein reference characters  66   a  and  66   b  are packing surfaces extending along and abutting against the peripheral edge of the closing plate  56 . A packing surface  67  is further provided to divide a space surrounded by the packing surfaces  66   a  and  66   b  into front and rear sections. The rear portion of the engine mount case  4  is in abutment against the lower surface of the cylinder head  21  through the packing surface  68  and is provided with an exhaust passage  69  communicating with the exhaust passage  47 . 
     The engine mount case  4  has peripheral walls  70   a  and  70   b  extending downwardly from the packing surfaces  66   a  and  66   b , respectively, and an enclosure wall  71  extending downwardly from the packing surface  67  (FIG.  7 ). All of the peripheral walls  70   a  and  70   b  and the enclosure wall  71  extend to positions lower than the flywheel  58 . The periphery of the flywheel  58  is surrounded by the peripheral wall  70   b  and the enclosure wall  71 . The lower end of the peripheral wall  70   a  is connected to a bottom plate  72   a , and the lower end of the peripheral wall  70   b  is connected to a bottom plate  72   b . These bottom plates  72   a  and  72   b  extend to positions below the central portion of the flywheel  58 . However, the height (i.e., depth) of the peripheral wall  70   b  as measured from the packing surfaces  66   a ,  66   b  and  67  is lower than the height (i.e., depth) of the peripheral wall  70   a  and hence, the bottom plates  72   b  and  72   a  are superposed on each other in a vertically spaced apart relation below the central portion of the flywheel  58 , and a mounting front opening  73  is defined therein to open forwardly. 
     The driving shaft  10  for transmitting the rotation of the crankshaft  9  to the propeller  13  is carried in the bottom plates  72   b  and  72   a  to vertically extend through the opening  73 . An upper end of the driving shaft  10  is inserted from below into an internal bore  60   b  (FIG. 8) in the collar member  60  fitted to and spline-engaged with the crankshaft  9 . 
     The connecting member  19  for connecting the swivel shaft  18  and the engine mount case  4  to each other is also inserted from front into the opening  73 . The connecting member  19  includes two left and right connecting rods  19   a  and  19   b  to extend longitudinally on opposite sides of the driving shaft  10 . Tip ends of the connecting rods  19   a  and  19   b  are connected to the engine mount case  4  through a mount rubber  74 . 
     FIG. 10 is a plan view of the engine mount case as viewed from below. A mounting surface  75  is formed into an annular shape on the lower surface of the engine mount case  4  (lower surface of the bottom plate  72   a ). Thus, the engine  7  is mounted on the extension case  5  through the engine mount case  4  by clamping the engine mount case  4  to the peripheral edge of the upper end of the extension case  5  with the mounting surface  75  interposed therebetween. 
     An annular oil pan mounting surface  76  is also formed on the lower surface of the engine mount case  4  inside the mounting surface  75 , and a peripheral edge of an upper end of an oil pan  77  is fastened to the oil pan mounting surface  76  by bolts  78 , as shown in FIG.  7 . An opening  79  in an upper surface of the oil pan  77  communicates with the inside of the engine block  20  through an oil communication passage  80  defined in the engine mount case  4  and an opening  81  provided in the closing plate  56 . Oil which is returned from the crank chamber and accumulated on the closing plate  56  is passed through the opening  81  and the oil communication passage  80  and dropped from the opening  79  Into the oil pan  77 . However, the opening  81  is provided on the side opposite from the flywheel  58  with respect to the enclosure plate  71  of the closing plate  56 . Therefore, the oil on the closing plate  56  cannot enter a portion of the flywheel  58  which is surrounded by the peripheral wall  70   b  and the enclosure wall  71 . 
     An exhaust pipe portion  77   a  is integrally formed at an upper portion of the oil pan  77  to protrude rearwardly. and an exhaust passage  82  is defined in the exhaust pipe portion  77   a  to communicate with the exhaust passage  69  in the engine mount case  4 . The exhaust passage  82  communicates with a catalytic converter  83  juxtaposed outside the oil pan  77 , and an exhaust gas purified in the catalytic converter  83  is passed through an exhaust pipe  84  and discharged from the lower portion of the extension case  5  into water. 
     The oil stored in the oil pan  77  is drawn through a strainer  85  and an intake pipe  86  into an oil pump  87  and supplied from the oil pump  87  to various portions of the engine. The oil pump  87  is driven by the crankshaft  9  through a gear train  88  (see FIG.  8 ). 
     In general, the center of gravity center of the outboard motor body is offset toward the center of the engine due to an influence of the heavy engine carried at the upper portion and is at a location higher than the tilting shaft. In the above-described embodiment, however, the flywheel  58  which was located at the uppermost portion of an engine in the prior art, is now provided at the lower end of the crankshaft  9 , i.e., at the lower portion of the engine  7 . Therefore, the gravity center of the engine  7  and thus the gravity center of the outboard motor body  1  is lowered to near the tilting shaft  16 . Therefore, only a reduced moment is required to swing the outboard motor body  1  upwardly about the tilting shaft  16 , thereby enabling an easy tilting-up or a prompt tilting-up. 
     The flywheel  58  provided at the lower portion of the engine  7  is accommodated in a space between the engine block  20  and the connecting member  19 . Therefore, the entire height of the outboard motor body  1  is relatively low. Further, the flywheel does not exist above the pulley  52  and hence, even if the pulley  52  is made sufficiently small in diameter, there is no problem in handling the pulley. Thus, the pulley  53  may have a small diameter, leading to a reduction in size of the outboard motor body  1 . 
     Notwithstanding that the flywheel  58  protrudes downwardly, the engine  7  can be easily placed at a predetermined location through the engine mount case  4  having the peripheral wall  70  extending below the flywheel  58  and particularly, can be easily and satisfactorily mounted on the outboard motor body  1 . 
     In addition, since the flywheel  58  has the upper and lower portions covered by the closing plate  56  and the bottom plate  72 , and its periphery is covered by the peripheral wall  70   b  and the enclosure wall  71  it is unlikely that, water will enter the area of the flywheel  58  from the outside and hence, the dynamo can be mounted without any influence exerted to positions around the dynamo  64 . 
     Further, the engine  7  in the present embodiment can also be utilized as a horizontal power source with the crankshaft  9  arranged horizontally, by sealing the opening  81  in the closing plate  56 , or by replacing the closing plate  56  itself and removing the oil pan  77 . 
     In the starter motor  48  of the engine  7 , the output shaft  49  thereof protrudes downwardly from the motor body to engage, from above, the ring gear  65  formed on the flywheel  58  located below the starter motor  48  and hence, the need to water proof such portion of the motor  48  can be avoided. 
     In the engine  7 , the power take-off driving shaft  10  and the flywheel  58  are mounted at the same end of the crankshaft  9  and therefore, the vibration of the engine due to the crankshaft  9  is reduced. 
     A second embodiment of the present invention will now be described with reference to FIGS. 13 to  19 . Reference numerals used in the first embodiment are basically different from those used in the second embodiment, and the same reference numeral may not necessarily designate the same element. 
     FIG. 13 is a side view of the entire outboard motor  1  to which the present invention is applied. Reference character  1   a  is an outboard motor body casing which includes an extension case  2 , a gear case  3  and the like. An engine  4  is mounted at an upper portion of the outboard motor body casing la and has an upper portion covered with an engine cover  5 . 
     The outboard motor  1  is mounted at a stern  7  through a mounting means  6 . The mounting means  6  includes a bracket  8  fixed to the stern  7  through bolts, and a swivel case  10  pivotally mounted for vertically swinging movement to the bracket  8  through a tilting shaft  9  mounted to laterally extend over the entire length of the bracket  8 . A swivel shaft  11  is rotatably carried in the swivel case  10  in a vertically directed manner. The outboard motor  1  is connected to the swivel shaft  11  through upper and lower connecting members  12  and  12   a . Thus, the outboard motor  1  is swingable vertically about the tilting shaft  9  and turnable laterally about an axis of the swivel shaft  11 . 
     The engine  4  has a crankshaft  13  vertically directed, and a driving shaft  14  is connected to the crankshaft  13  and extends downwardly within the extension case  2  to reach the inside of the gear case  3 . The driving shaft  14  is connected at its lower end to a propeller shaft  16  through a forward and backward movement changing device  15  within the gear case  3 . A propeller  17  is rotatively driven by an engine power transmitted via the crankshaft  13 , the driving shaft  14 , the forward and backward movement changing device  15  and the propeller shaft  16 . Reference character  18  is an operating shaft for changing the forward and backward movements, which is rotatably provided to extend upwardly through the swivel shaft  11 . 
     FIG. 14 is a vertical sectional view of the engine  4 . The crankshaft  13  is directed vertically, as described above. As can be seen from FIG. 13, the engine  4  is mounted with the crankshaft  13  located toward a front portion of the outboard motor  1  (toward a boat). In FIG. 14, the right side corresponds to the front side of the outboard motor  1 . 
     An engine body of the engine  4  includes a main block  19 , a cylinder head  20  and a cylinder head cover  21 . The main block  19  is constructed by integrally connecting a cylinder block  19   a  integrally provided with a skirt forming a half of a crankcase with a remaining crankcase portion  19   b  by bolts  22   a  (FIGS.  16  and  17 ). Four cylinders  23  are arranged in a row within the main block  19 . Thus, the engine  4  is an inline 4-cylinder, 4-cycle engine, in which pistons  24  are connected to the vertically directed single crankshaft  13  through connecting rods  25 . The crankshaft  13  in rotatably carried in the main block  19  in a manner that it is fastened by bolts  22   b  mounted in the cylinder block  19   a  and crankcase portion  19   b  and is sandwiched between opposed bearings. 
     A camshaft  27  is vertically disposed within a valve operating chamber  26  defined in the cylinder head  20 . The cam shaft  27  is driven by the crankshaft  13  through a belt-drive transmission  31  which includes a driving pulley  28  mounted at an upper end of the crankshaft  13  protruding from the main block  19 , a driven pulley  29  mounted at an upper end of the cam shaft  28  protruding from the cylinder head  20 , and a belt  30  wound around the pulleys  28  and  29 . The cam shaft  27  is in engagement with intake and exhaust valves for each cylinders  23  through rocker arms to control the motions of these intake and exhaust valves. That is, the belt drive transmission  31  forms a portion of a valve operating device for the engine  4 . 
     The driving shaft  14  is connected to a lower end  13   b  of the crankshaft  13  protruding from the main block  19  and extends downwardly within the extension case  2 , as described above. A disk-like flywheel  32  is further fastened to the lower end  13   b  by screws  33  to extend parallel to a lower surface of the main block  19 . A dynamo  34  is mounted at the upper end  13   a  of the crankshaft  13  above the valve-operating driving pulley  28 , with its rotor  35  fastened to the upper end  13   a  by a screw  36 , so that it is rotated in unison with the crankshaft  13 . 
     In this embodiment, the flywheel  32  is formed into a relatively thin disk-shape, and a low-level skirt portion (an upper case portion)  37  is integrally formed at a lower portion of the main block  19  and opens downwardly. The flywheel  32  is accommodated within the skirt  37 . A mount case (lower case portion)  38  is mounted to a flat lower surface of the skirt portion  37  by bolts. The engine  4  is mounted in the extension case  2  through the mount case  38 . The skirt portion  37  is provided with an enclosure wall  37   a  which surrounds an outer periphery of the flywheel  32 . 
     The flywheel  32  basically has a required inertial mass only by itself, but is capable of distributing the inertial mass, inclusive of the rotor  35 . 
     The rotor  35  is vertically high in level, as compared with the flywheel  32 , but has a smaller diameter and has an inertial mass far less than that of the flywheel  32 . Therefore, the diameter of the crankshaft end  13   a  adjacent the rotor  35  can be reduced and as a result, the diameter of the driving pulley can be reduced. If the diameter of the driving pulley is reduced, the diameter of the driven pulley  29  requiring a diameter twice the diameter of the driving pulley can be correspondingly reduced, which is convenient for reducing the overall size of the engine. 
     The belt-drive transmission  31  and the dynamo  34  are covered from above with a cover member  40 . The cover member  40  is formed such that a portion corresponding to the dynamo  34 , i.e., a portion near the front portion of the engine  4  is raised, and a rear portion is lowered to extend along the belt-drive transmission  31 . The entire cover member  40  shown is integrally formed. The cover member  40  however may be vertically divided into a portion which covers the wrapping type transmission  31 , and a portion which covers the dynamo  34 , or longitudinally divided into a portion which covers a rear portion of the belt-drive transmission  31 , and a portion which covers a front portion of the belt-drive transmission  31  and the dynamo  34 . 
     Below the main black  19 , a portion of the skirt  37  enclosing the outer periphery of the flywheel  32  by the enclosure wall  37   a  protrudes in a circular shape on opposite sides and forwardly (FIGS.  16  and  17 ). A similar protruding portion  38   a  is also provided on an upper and front portion of the mount case  38  in a face-to-face relation to this protruding portion of the skirt  37  (FIGS.  14  and  16 ). An-opening in the protruding portion of the skirt  37  is closed from below by the protruding portion of the mount case  38 . This protruding configuration results in an enhanced rigidity of a surrounding portion. 
     An oil pan  57  is mounted in a depending or hanging-down manner on a flat lower surface of the mount case  38  formed below the protruding portion and near a rear portion, and is accommodated in the extension case  2 . The inside of the mount case  38  is divided into a portion  38   b  defining an accommodating chamber for the flywheel  32  and a portion  38   c  communicating with the oil pan  57  by a partition wall  58  abutting against an end face of the enclosure wall  37   a.    
     As shown in FIG. 16, the mount case  38  is fastened on its lower surface to an upper end of the extension case  2  by bolts  76 . More specifically, the engine  4  is mounted in the extension case  2  through the mount case  38  and accommodated in an engine room  41  having its upper portion defined by the engine cover  5 , but a lower portion of the engine room  41  is defined-by an undercase  77  (FIGS. 13,  15  and  16 ) which is supported at a peripheral edge of its lower end on the mount case  38  to cover the lower portion of the engine and which opens upwardly. FIG. 15 is a view of the inside of the engine room  41  as viewed from the opposite side from FIGS. 13 and 14 in vertical section of the cover member covering the engine  4 , wherein the lower portion of the engine  4  is shown in a sectional view similar to that of FIG.  14 . 
     The engine cover  5  is detachably mounted to the undercase  77  through a mating face  78  to cover an opening provided in an upper portion of the undercase  77 . The outer periphery of a mount case  38  and the extension case  2  in the vicinity of a connection is covered by an undercover  80  which is fastened to the undercase  77  by a screw  79  (FIG.  15 ), and the outboard motor body  1   a  has a gentle profile provided by the undercase  77 , the undercover  80  and the extension case  2 . 
     The upper surface of the engine cover  5  is formed into a shape corresponding to the cover member  40  (FIGS. 15,  18  and  19 ). More specifically, the engine cover  5  is formed in such a manner that a front portion  5   a  thereof corresponding to the dynamo  34  is higher in level, and a rear portion  5   b  of the cover  5  is lower in level. An air intake device  42  having a pair of left and right passage members  43  is disposed on this rear portion  5   b  formed at the lower level. As shown in FIG. 19, each of the passage members  43  is connected to a peripheral edge of an opening  5   c  provided in the engine cover portion  5   b  and extends upwardly, and further has a notched air introducing portion  43   a  provided at an upper opening edge. 
     The passage members  43  are covered at their upper portions with a cover member  45 . The cover member  45  is fixed to the engine cover  5  by a bolt  44  at an intermediate forward position between the left and right passage member  43 . The cover members  45  includes an upper plate portion  45   a  which covers the upper portion of the passage member  43 , and a side plate portion  45   b  pendent along laterally opposite edges of the upper plate portion  45   a . The passage member  43  raised on the lower engine cover portion  5   b  extends behind the dynamo  34  up to substantially the same level as the dynamo  34 , so that it is superposed with the dynamo  34  laterally. An upper surface of the cover member  45  rearwardly extends flush with the upper surface of the front engine cover  5   a  without protrusion from the upper surface of the front engine cover  5   a.    
     The open air is permitted to freely flow through a rear opening into a space defined above the engine cover portion  5   b  covered at its upper portion and opposite sides by the cover member  45 , and is guided via the passage members  43  into the engine room  41  as shown by an arrow a in FIG.  18 . Such air is used as an intake gas for the engine  4  to cool the periphery of the engine. 
     FIG. 17 is a schematic plan view illustrating the arrangement of the engine  4  and auxiliaries within the engine room  41 . Reference character  46  is an intake valve;  47  is an exhaust valve; and  48  is a rocker arm. A valve mechanism comprising these members is provided for every cylinder  2  and controlled in opening and closing by the cam shaft  27 . Reference character  49  is an intake port provided in the cylinder head  20 . An intake pipe  50  is connected to the intake port  49  and extends forwardly along the side of the engine  4 . A portion of air introduced via the passage members  43  into the engine room  41  is drawn into the Intake pipe  50  at a front end thereof and then via the intake port  49  into the cylinder  23 . Reference character  51  is a carburetor, and  51   a  is an intake silencer. Such intake pipes  50  are provided for each cylinder  23  and vertically juxtaposed along the side of the engine  4 . 
     At the other side of the engine  4 , an exhaust passage  52  extends vertically, and an exhaust port  53  corresponding to each of the cylinders  23  is in communication with the exhaust passage  52 . The exhaust passage  52  is connected to an upper end of an exhaust pipe (not shown) extending vertically within the extension case  2 , so that an exhaust gas is passed through the exhaust pipe and released at a lower end of the exhaust pipe into water. 
     On the same side of the engine as the exhaust passage  52 , an electrical equipment box  54  in which electric equipments are accommodated forwardly, and a starter motor  55  is disposed below the box  54  (see FIGS.  15  and  16 ). Reference character  54   a  is a spark plug wire which is connected to a spark plug provided in the side of the cylinder head  20 . An igniting coil  54   b , a CDI unit  54   c  and the like are accommodated in the electrical equipment box  54 , but since the engine in the present embodiment is the 4-cycle, 4-cylinder engine, ignition can be achieved with only two coils  54   b  in total, one for two cylinders. These coils are disposed reasonably in a space above the starter motor  55 , and the CDI unit  54   c  is disposed in a location closer to the front, which would not interfere with the starter motor  55 . An output shaft  55   a  of the starter motor  55  is gear-meshed with a ring gear  56  (FIGS. 14,  15  and  16 ) which is mounted around the outer periphery of the flywheel  32 . 
     As shown in FIG. 14, an oil intake pipe  60  having a strainer  59  at a lower end thereof extends upwardly from a bottom of an oil pan  57  through an oil pan communication portion  38   c  of the mount case  38  and is connected to an oil intake passage  61  defined in a lower portion of the main block  19 . The oil intake passage  61  is in communication with an intake port  63  in an oil pump  62  which is provided at the lower end of the camshaft  27  and driven by the cam shaft  27 . 
     Oil pressurized by the oil pump  62  is fed to various bearing portions around the camshaft  27  and via an oil passage (not shown) provided through the cylinder head  20 , the cylinder block  19   a  and the crankcase  19   b  to an oil filter  68  mounted to the front surface of the crankcase  19   b . The oil leaving the oil filter  68  flows into an oil passage  69  (see FIG. 17) vertically located in a laterally central portion of the front surface of the crankcase  19   b  and is further passed through an oil passage  70  to reach main bearings  39  of the crankshaft  13  to lubricate these bearings. 
     Further, the oil flows through an oil passage  72  provided in the crankshaft  13  to reach a crank pin bearing  71  and the inside of the cylinder  23  to lubricate the crank Pin bearing  71  and the inner surface of the cylinder. The cylinders  23  vertically arranged in a row are in communication with one another at locations closer to the crank chamber through oil bores  73 , so that the oil in each cylinder  23  flows down In sequence through these oil bores  73  and is discharged from the lowermost oil bore  73   a  to a portion in the vicinity of the lower end of the crank shaft  13 . However, this oil cannot flow into a chamber accommodating the flywheel  32 , and is permitted to flow through an oil passage  82  (FIG. 16) for returning of the oil between the main bearing  39  at the lower end and a crankshaft oil seal  81  and through a return oil passage  83  (FIG. 16) for returning of the oil around the outside of the flywheel accommodating chamber to the oil pan communication portion of the mount case  38  and then returned into the oil pan  57 . 
     Oil which has lubricated the portion around the cam shaft  27  is passed through an oil passage  74  to an oil return bore  65  and returned via an oil return passage  64  and an oil return pipe  66  to the oil pan  57 . The oil pan  57  extends from the mount case  38  into the extension case  2 , thereby ensuring that the height of engine  4  mounted cannot be increased. A drain plug  84  is provided at a front end of the bottom of the oil pan  57  to face a recess  85  defined in the extension case  2  as shown in FIG.  15 . Alternatively, a recess  85  may be provided in the side of the extension case  2  to face the drain plug  84 . 
     The mount case  38  is connected to the pair of left and right connecting members  12  (FIG. 13) through a rubber mount  75  which extends laterally. The rubber mount  75  includes a core member  75   a  and a rubber  75   b  which surrounds the core member  75   a , and the connecting member  12  is connected to the core member  75   a  by a bolt.