Abstract:
An outboard engine has an internal combustion engine as a prime mover, a throttle valve device including a valve element and a valve shaft supporting the valve element, and combined with the internal combustion engine, a driven unit combined with the throttle valve device, and a drive unit for driving the driven unit. The drive unit is capable of smoothly transmitting an external throttle-operating force to the driven unit regardless of its position. A throttle valve operating mechanism connects an operating lever included in the driven unit, and a throttle-operating Bowden cable included in the drive unit. The throttle valve operating mechanism is a linkage including plural links. Joints joining the adjacent joining parts of those links are ball-and-socket joints, respectively. The valve shaft has one end connected to the operating lever and the other end connected to a throttle position sensor. The valve shaft is inclined to a horizontal plane.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. 119, based on each of the following patent applications: 
     Japanese Patent Application No. 2003-181794, filed on Jun. 25, 2003; 
     Japanese Patent Application No. 2003-181795, filed on Jun. 25, 2003; 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an outboard engine provided with an internal combustion engine having a throttle valve device capable of being easily operated from outside the outboard engine and of being neatly arranged inside an engine cover covering the internal combustion engine. 
     2. Description of the Related Art 
     A prior art outboard engine provided with an internal combustion engine and a throttle valve device combined with the internal combustion engine, and disclosed in JP 8-91297 A uses a push-pull cable, namely, a Bowden cable, for transmitting a throttle operating force to a driven part of the throttle valve device. 
     In the outboard engine disclosed in JP 8-91297 A, the inner cable of the Bowden cable is connected to a control lever disposed in a front part of the outboard engine, another cable is extended between a drive pulley combined with the control lever, and a driven pulley combined with the throttle valve device disposed in a rear part of the outboard engine. The inner cable of the Bowden cable is moved relative to the outer cable of the Bowden cable to turn the driven pulley in a desired direction for opening or closing the throttle valve device by the drive pulley. 
     Since the drive and the driven pulley respectively having certain diameters are used for transmitting the sliding motion of the inner cable of the Bowden cable to the valve shaft of the throttle valve device, a comparatively large space available for placing the drive and the driven pulley must be formed around the throttle valve device and hence the size of the engine cover needs to be increased. 
     In most conventional outboard engines, a vertical internal combustion engine is disposed with its crankshaft extended in a vertical position in a front part of the outboard engines, an intake duct connected to the intake port of the internal combustion engine is extended on the right or the left side of the internal combustion engine, and the intake duct and a throttle valve device connected to the intake duct are placed inside an engine cover covering the internal combustion engine. In the following description, terms qualifying directions and sides, such as right, left, front, rear, longitudinal and lateral, are used to qualify directions and sides with respect to the advancing direction of a ship provided with the outboard engine. 
     In most cases, a valve shaft holding the throttle valve of the throttle valve device is vertically extended, a throttle lever for turning the throttle valve has a base part connected to the upper or the lower end of the valve shaft and a free end connected directly or through links to an operating member, such as a push-pull wire. 
     In the outboard engine of this type, the valve shaft is supported in an upper bearing part and a lower bearing part, and water collects in the lower bearing part and, in some cases, the water collected in the lower bearing part hinders the light operation of the throttle valve device. 
     An outboard engine disclosed in JP 11-34985 A is provided with a throttle valve device having a throttle valve supported on a valve shaft, and placed in an intake duct with the valve shaft extended in a horizontal position. 
     In the outboard engine disclosed in JP 11-34985 A, a throttle lever connected to the valve shaft supporting the throttle valve, and a link connecting the throttle lever to a push-pull wire are arranged outside the intake duct, and a throttle position sensor for measuring the angular position of the throttle valve is connected to an outer end, lying outside the intake duct, of a shaft supporting a turning lever connecting the throttle lever and the push-pull wire. When the throttle lever, the link and the throttle position sensor are arranged outside the intake duct, the engine cover covering the internal engine of the outboard engine needs to be formed having a bulge and it is difficult to form the outboard engine in a compact construction. 
     The present invention has been made in view of the foregoing problems and it is therefore an object of the present invention to provide an outboard engine provided with a throttle valve device requiring a small space for installation, and a small engine cover that does not need to be formed having a bulge. 
     SUMMARY OF THE INVENTION 
     An outboard engine in a first aspect of the present invention includes: an internal combustion engine; a throttle valve device for controlling intake air to be taken in by the internal combustion engine; a driven unit combined with the throttle valve device; a drive unit for producing a throttle-driving force corresponding to an external throttle-operating force applied thereto; and a throttle valve operating mechanism for transmitting the throttle-operating force of the drive unit to the driven unit; wherein the throttle valve operating mechanism is a linkage including a plurality of component members, and the plurality of component members are joined by ball-and-socket joints. 
     In the outboard engine according to the present invention, the driven unit combined with the throttle valve device, and the drive unit capable of producing the throttle-operating force are interlocked by the throttle valve operating mechanism, and the throttle-operating mechanism is the linkage. Therefore, the throttle-operating force of the drive unit can be smoothly transmitted to the driven unit regardless of the distance between the drive unit and the driven unit. 
     Since the throttle-operating mechanism is a linkage, the throttle-operating force of the drive unit can be surely transmitted to the driven unit. 
     Since the throttle operating mechanism is a linkage, and the links of the linkage are joined by the ball-and-socket joints, respectively, the throttle-operating force of the drive unit can be surely transmitted to the driven unit regardless of the positional relation between the driven unit and the drive unit, and regardless of the difference between a direction in which the throttle-operating force of the drive unit acts and a direction from which the driven unit receives the throttle-operating force. 
     Preferably, the throttle valve device is disposed with the valve shaft inclined to a horizontal plane. The throttle valve device may be disposed such that the valve shaft slopes down from its front end toward its rear end. 
     When the throttle valve device is disposed in the foregoing position, collection of water in bearing parts supporting the valve shaft can be prevented and the throttle valve device can be lightly operated. 
     Preferably, the linkage including the throttle valve device is disposed such that the valve shaft slopes down from a front end thereof toward its rear end. 
     Preferably, the linkage includes a swing arm pivotally supported so as to be turned by the throttle-operating force of the drive unit, a bell crank, a link connecting the swing arm to the bell crank to transmit the swing motion of the swing arm to the bell crank, and a first connecting rod for transmitting motions of the bell crank to the driven unit. 
     Preferably, the arm, the bell crank and the link are supported on a single bracket. 
     Preferably, a second connecting rod for transmitting the throttle-operating force of the drive unit to the arm is longitudinally extended, and the first connecting rod for transmitting the motion of the bell crank to the driven unit is laterally extended. 
     Joints joining adjacent joining parts of the arm, the bell crank, the link and the two connecting rods may be ball-and-socket joints, respectively. 
     An outboard engine in a second aspect of the present invention includes: an internal combustion engine, an engine cover covering the internal combustion engine; and a throttle valve device disposed inside the engine cover and provided with a throttle valve for controlling intake air to be taken in by the internal combustion engine; wherein the throttle valve is supported on a valve shaft, a driven unit to be driven by an external throttle-operating force is combined with one end of the valve shaft, a throttle position sensor is combined with the other end of the valve shaft, and the valve shaft is inclined to a horizontal plane. 
     In this outboard engine, a dimension of the throttle valve along the valve shaft is small and the throttle valve device is compact and can be neatly disposed inside the engine cover. 
     Since the valve shaft of the throttle valve is inclined at a small angle to a horizontal plane, collection of water in bearing parts supporting the valve shaft can be prevented and the throttle valve device can be lightly operated. 
     The driven unit and the throttle position sensor combined with the opposite ends of the inclined valve shaft of the throttle valve can be inclined so as to be substantially parallel to the inclined surfaces and curved surfaces of the engine cover and can be disposed close to the engine cover covering the internal combustion engine. Consequently, the internal combustion engine can be neatly disposed inside the engine cover. 
     Preferably, the internal combustion engine has a crankshaft disposed in a crankcase on the front side of the center of the outboard engine with respect to the longitudinal direction, and the throttle valve device is disposed in front of the crankcase, and the valve shaft is extended along a longitudinal surface of the outboard engine. 
     Thus, the intake duct having one end connected to intake ports formed in a cylinder head on the rear side can be extended along either the right or the left side surface of the internal combustion engine and around the front side of the crankcase. Therefore, the engine cover does not need to be formed having a bulge, the intake duct can be formed having a long length, the outboard engine can be formed having compact construction, and intake efficiency can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation of an outboard engine in a preferred embodiment according to the present invention taken from the right side of the outboard engine; 
         FIG. 2  is a partly cutaway plan view of the outboard engine shown in  FIG. 1 ; 
         FIG. 3  is an enlarged plan view of an essential part of the outboard engine shown in  FIG. 1 ; 
         FIG. 4  is a fragmentary, longitudinal sectional view taken on the line IV—IV in  FIG. 1 ; 
         FIG. 5  is a view taken in the direction of the arrow V in  FIG. 2 ; 
         FIG. 6  is an exploded perspective view of a throttle-operating mechanism; 
         FIG. 7  is a perspective view of the throttle-operating mechanism shown in  FIG. 6 ; 
         FIG. 8  is a plan view of a link; 
         FIG. 9  is a plan view of the link shown in  FIG. 8 ; 
         FIG. 10  is a cross-sectional view taken on the line X—X in  FIG. 8 ; 
         FIG. 11  is a cross-sectional view taken on the line IX—IX in  FIG. 8 ; and 
         FIG. 12  is a plan view of a joint for a connecting rod. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The construction of an outboard engine  1  in a preferred embodiment of the present invention shown in  FIGS. 1 to 12  will be described. 
     The front side of the outboard engine  1  on the side of a ship, i.e., the right side as viewed in  FIG. 1 , is supported by a support device  3  on the transom  2  of the ship. The outboard engine  1  has an extension case  4  covering a lower part of the outboard engine  1 , an under cover  5  joined to the upper end of the extension case  4 , and an engine cover  6  detachably joined to the upper end of the under cover  5 . The engine cover  6  has an air intake opening  6   a . A gear case  7  is joined to the lower end of the extension case  4 . A propeller P extends rearward from the gear case  7 . 
     An expanded upper part of the under cover  5  and the engine cover  6  define an engine chamber  8 . An inline four-cylinder four-stoke-cycle internal combustion engine  10  and auxiliary machines are placed in the engine chamber  8 . The internal combustion engine  10  is disposed with its crankshaft  9  extended in a vertical position. As shown in  FIG. 4 , a flywheel  9   a  is mounted on the lower end of the crankshaft  9 . 
     Referring to  FIG. 1 , the internal combustion engine  10  has a crankcase  11 , a cylinder block  12  and a cylinder head arranged in that order rearward and joined together. The crankshaft  9  is supported for rotation between the joining surfaces of the crankcase  11  and the cylinder block  12 . The cylinder block  12  is provided with four cylinders  14  in a vertical arrangement. As shown in  FIG. 2 , pistons  15  are fitted in the cylinders  14  for longitudinal, sliding reciprocation, and are connected to the crankshaft  9  by connecting rods  16  ( FIG. 4 ) to drive the crankshaft  9  for rotation. 
     As shown in  FIG. 2 , ignition plugs, not shown, are attached to the cylinder head  13  so as to be exposed to combustion chambers  17  defined by the cylinders  14 , the pistons  15  and the cylinder head  13 , respectively. An intake port  18  and an exhaust port  19  for each of the cylinders  14  are formed in a lateral arrangement in the cylinder head  13  so as to open into the combustion chamber  17 . An intake valve  20  and an exhaust valve  21  are seated on the inner open ends, on the side of the combustion chamber  17 , of the intake port  18  and the exhaust port  19  of each cylinder  14 , respectively. A fuel injection valve, not shown, is placed in the intake port  18 . The intake valves  20  and the exhaust valves  21  are opened and closed by valve trains, not shown. 
     An intake vessel  22  defining an intake chamber is disposed in an upper right-hand region (a right region in  FIG. 2 ) of a front part of the engine chamber  8 . The inlet ends (right ends in  FIG. 2 ) of the intake ports  18  are connected through an intake manifold  23  and a throttle valve device  34  to the intake box  22 . A fuel injector i is provided at the downstream end of the intake manifold  23 . The intake box  22  is opened through an intake duct  33  into the atmosphere as shown in  FIG. 4 . 
     The support device  3  has a main support  24  including a swivel case  25 . A shaft, not shown, attached to a mount frame is supported for turning in a horizontal plane on the swivel case  25 . An upper mount frame  26  of the mount frame is connected to a mount case  30  formed integrally with a lower part of the internal combustion engine  10  by an upper mount rubber  28 . A lower mount frame  27  of the mount frame is attached to the extension case  4  by a lower mount rubber  29 . A steering arm  31  formed in the mount frame is turned in a horizontal plane to turn the outboard engine  1  laterally for steering on the swivel case  25 . 
     The main support  24  is supported on the transom  2  by a horizontal tilt shaft  32  and can be turned in a vertical plane on the tilt shaft  32 . 
     Referring to  FIGS. 2 and 3 , the throttle valve device  34  has a cylindrical valve case  35 , and a longitudinal valve shaft  36  supported for turning on the valve case  35 . The valve shaft  36  is slightly inclined at an angle θ ( FIG. 4 ) to a horizontal plane such that its front end is at a level higher than that of its rear end. The throttle valve device  34  has a disk-shaped valve element  37  attached to the valve shaft  36 , an operating lever  38  supported for turning on a rear part of the valve case  35 , and an interlocking mechanism  39  interlocking the valve shaft  36  and the operating lever  38 . The interlocking mechanism  39  turns the valve shaft  36  such that a turning angle through which the operating lever  38  needs to be turned to turn the valve element  37  through a unit angle when the valve element  37  is near its fully closed position is greater than a turning angle through which the operating lever  38  needs to be turned to turn the valve element  37  through the same unit angle when the valve element  37  is near its fully open position. A throttle position sensor  57  is disposed on a front part of the valve case  35 . The front end of the valve shaft  36  is connected to a movable member  57   a  of the throttle position sensor  57 . 
     Although the interlocking mechanism  39  in this embodiment is a cam mechanism, the interlocking mechanism  39  may be any suitable mechanism, such as a linkage or an elliptic-gear mechanism, provided that the mechanism has the same characteristics as the interlocking mechanism  39 . 
     A throttle valve operating mechanism  40  for operating the throttle valve device  34  will be described. 
     Referring to  FIG. 5 , the operating lever  38  of the throttle valve device  34  is provided at its free end with a ball-ended connecting member  38   a . The ball-ended connecting member  38   a  deviates from a shaft  38   b  on which the operating lever turns. The ball of the ball-ended connecting member  38   a  is engaged in a socket  41   a  of a socket-ended connecting member  41  provided with an internally threaded hole  41   b  ( FIG. 12 ). The ball of the ball-ended connecting member  38   a  and the socket  41   a  constitute a ball-and-socket joint. An externally threaded part  42   a  of a rod  42  is screwed in the internally threaded hole  41   b , and a locknut  43  put on the externally threaded part  42   a  is screwed down firmly against the end of the socket-ended connecting member  41  to connect the socket-ended connecting member  41  securely to the left end of the rod  42 . The socket-ended connecting member  41  is able to turn in all planes passing the center of the ball of the ball-ended connecting member  38   a  attached to the free end of the operating lever  38 . As shown in  FIGS. 2 and 3 , a socket-ended connecting member  58  similar to the socket-ended connecting member  41  is attached to the right end of the rod  42 . 
     Referring to  FIGS. 3 and 6 , a bracket  44  is fastened to the right side wall of the crankcase  11  of the internal combustion engine  10  with a bolt  45  passed through a through hole  44   a  formed in the bracket  45 . A pivot shaft  46   a  supporting a bell crank  46  is supported for rotation in bearings  47  in a vertical hole  44   b  formed in the bracket  44 . A washer  48  is put on a lower end part of the pivot shaft  46   a , and a snap ring  49  is engaged in an annular groove  46   b  formed in a lower part of the pivot shaft  46   a  to retain the bell crank  46  on the bracket  44 . A ball-ended connecting member  46   d  is attached to the front arm  46   c  of the bell crank  46  so as to extend upward. A ball-ended connecting member  46   f  is attached to the rear arm  46   e  of the bell crank  46  so as to extend downward. The ball-ended connecting member  46   d  attached to the front arm  46   c  of the bell crank  46  is engaged in the socket of the socket-ended connecting member attached to the right end of the rod  42 . The ball-ended connecting member  46   d  and the socket-ended connecting member  58  constitute a ball-and-socket joint. 
     Referring to  FIGS. 8 to 11 , a front end part  50   a  of a link  50  has substantially horizontal, parallel, flat upper and lower surfaces, and is provided with a socket  50   b . The ball-ended connecting member  46   f  attached to the rear arm  46   e  of the bell crank  46  is engaged in the socket  50   b  of the link  50 . A hole  50   c  is formed in a part of the link  50  on the front side of the socket  50   b . The sockets  50   b  and  50   c  are connected by a slit  50   d . A rear end part  50   e  of the link  50  has parallel right and left flat surfaces extending substantially along front and rear vertical planes. A socket  50   f , a hole  50   g  and a slit  50   h  similar to those fanned in the front end part  50   a  are formed in the rear end part  50   e . The ball-ended connecting member  46   f  attached to the rear arm  46   e  of the bell crank  46  is engaged in the socket  50   b  of the front end part  50   a  of the link  50  so form a ball-and-socket joint. 
     As shown in  FIG. 6 , a pivot shaft  44   c  projects rightward from a part, near the through hole  44   a  and the vertical hole  44   b , of the bracket  44 . An arm  51  is provided in the left side surface of a base part thereof with a cylindrical recess, not shown. The pivot shaft  44   c  of the bracket  44  is fitted in the cylindrical recess of the arm  51  to support the arm  51  for forward and backward turning. A holding bolt  52  passed through a through hole  51   a  formed coaxially with the cylindrical recess in the base part of the arm  51  is screwed in a center threaded hole  44   d  formed in the support shaft  44   c  of the bracket  44  to hold the arm  51  on the support shaft  44   c . A ball-ended connecting member  51   b  is attached to a middle part of the right side surface of the arm  51  so as to project rightward. The ball-ended connecting member  51   b  is engaged in the socket  50   f  of the rear end part  50   e  of the link  50  to form a ball-and-socket joint. A washer  53  is loosely put on the holding bolt  52 . 
     A connecting pin  54  is attached to the lower end of the arm  51  so as to extend rightward from the arm  51 . A connecting member  70  is swingably mounted on a free end part of the connecting pin  54 . 
     As shown in  FIG. 2 , a box  59  containing electrical equipment is disposed at a position above the right-hand side (on the left side as viewed in  FIG. 2 ) of the internal combustion engine  10 . 
     As shown in  FIG. 3 , a throttle operating Bowden cable  60  is connected to the throttle valve operating mechanism  40  to operate the throttle valve device  34 . The throttle operating Bowden cable  60  has a flexible cable  61  for transmitting operating force applied to an operating handle placed in a ship, not shown, to the throttle valve operating mechanism  40 , and a case  62  enclosing the cable  61 . A bracket  55  for holding the throttle operating Bowden cable  60  is attached to the under cover  5  in a right part of the engine chamber  8 . A holding pipe  63  having a neck  63   a  is put on a rear end part of the case  62 , and the neck  63   a  is forced into a slot  55   b  formed in a standing part  55   a  of the bracket  55  to hold case  62  of the throttle operating Bowden cable  60  on the bracket  55 . 
     A metal guide pipe  64  is connected to the rear end of the holding pipe  63 . The joint of the holding pipe  63  and the guide pipe  64  is covered with a sealing member  65 . The rear end  61   a  of the cable  61  is connected to the front end  66   a  of a connecting rod  66  in the guide pipe  64 . The connecting rod  66  extends rearward from the guide pipe  64 . A rear end part of the guide pipe  64  is covered with a sealing member  67 . An exposed part, extending forward from the under cover  5 , of the throttle operating Bowden cable  60  is covered with a rubber grommet  56  fitted in an opening  5   a  formed in the under cover  5 . 
     Referring to  FIG. 6 , the connecting rod  66  has an externally threaded rear end part  66   a . A locknut  68  is screwed on the externally threaded rear end part  66   a . The externally threaded rear end  66   a  is screwed in an internally threaded hole  71   a  formed in a body  71  of the connecting member  70 , and is fastened firmly to the connecting member  70 . 
     A sliding cover  72  is mounted on the body  71  of the connecting member  70 . The sliding cover  72  is able to slide longitudinally in a predetermined range. The connecting pin  54  attached to the lower end of the arm  51  is inserted in a hole  71   b  formed in the body  71  of the connecting member  70 , and a slot  72   a  formed in the sliding cover  72 . When the connecting rod  66  is pulled forward, the sliding cover,  72  slides forward relative to the body  71  by a predetermined stroke and thereby the connecting pin  54  is pulled forward and the arm  51  is turned forward. When the connecting rod  66  is pushed rearward, the connecting pin  54  engaged in the hole  71   b  of the body  71  is moved rearward and thereby the arm  51  is turned rearward. 
     Referring to  FIG. 7 , a shifting Bowden cable  69  for shifting a transmission is extended substantially parallel to the throttle operating Bowden cable  60  on the right side of the throttle operating Bowden cable  60 . The shifting Bowden cable  69  is held on the standing part  55   a  of the bracket  55 . When a crewman on board the ship pulls the throttle lever rearward to open the fully closed throttle valve device  34  of the outboard engine  1  embodying the present invention shown in  FIGS. 1  to  12 , the cable  61  of the throttle operating Bowden cable  60  is pulled forward. Consequently, the arm  51  having the lower end connected through the connecting member  70  and the connecting rod  66  to the rear end of the cable  61  is turned forward from a position shown in  FIG. 4  through an angle of about 90° at a maximum to turn the bell crank  46  counterclockwise, as viewed in  FIG. 3 , through an angle of 90° at a maximum. Consequently, the connecting rod  42  is moved leftward (upward, as viewed in  FIG. 3 ) to turn the operating lever  38  of the throttle valve device  34  counterclockwise, as viewed in  FIG. 5 , so that the fully closed throttle valve device  34  is opened. The angular position of the valve element  37  is measured by the throttle position sensor  57 . 
     When the operating lever  38  is turned through an angle in an opening direction with the throttle valve device  34  in a nearly fully closed state, the valve shaft  36  and the valve element  37  turn through a very small angle as compared with an angle through which the operating lever  38  is turned, owing to the agency of the interlocking mechanism  39  interlocking the valve shaft  36  and the operating lever  38 . Thus, the fine adjustment of the opening of the throttle valve device  34  is possible. 
     The cable  61  of the throttle operating Bowden cable  60  slides in a first direction, i.e., longitudinally, the rod  42  moves in a second direction, i.e., laterally to turn the operating lever  38  of the throttle valve device  34 , and the operating lever  38  is connected to the connecting rod  66  connected to the rear end of the cable  61  of the throttle operating Bowden cable  60  by the throttle valve operating mechanism  40  including the connecting member  41 , the rod  42 , the bell crank  46 , the link  50 , the arm  51  and the connecting member  70 . Although the first and second directions do not intersect, the second direction extends across the first direction when viewed in plan, as shown in  FIG. 3 . Therefore, even if the throttle valve device  34  is far off to the left from a rearward extension of the throttle operating Bowden cable  60 , the operating force can be surely transmitted through the cable  61  to the operating lever  38  and the throttle valve device  34  can be smoothly opened and closed. 
     Since the bracket  55  holding the throttle operating Bowden cable  60  is spaced a long distance apart from the arm  51 , and the rear end part of the throttle operating Bowden cable  60  is held on the bracket  55 , and the holding pipe  63  and the guide pipe  64  are easily tiltable, the cable  61  is able to slide smoothly in the case  62  and the connecting rod  66  is able to slide smoothly in the guide pipe  64  regardless of the vertical shifting of the connecting pin  54  attached to the lower end of the arm  51  even if the arm  51  is turned through a large angle and the connecting pin  54  of the arm  51  is shifted vertically by a long distance. 
     Since the bell crank  46  can be freely turned in a three-dimensional space by the tilting motion of the operating lever  38  and the longitudinal turning of the arm  51 , the swing motion of the arm  51  can be smoothly and surely transmitted to the operating lever  38 . 
     As shown in  FIGS. 3 and 4 , the operating lever  38 , i.e., a driven member of the throttle valve device  34 , is disposed at the rear end of the throttle valve device  34 , and the throttle position sensor  57  is disposed in front of the throttle valve device  34 . Therefore, the valve shaft  36  of the throttle valve device  34  is short, and hence the throttle valve device  34  can be neatly disposed in the space defined by the engine cover  6  covering the internal combustion engine  10 . 
     As shown in  FIG. 4 , the valve shaft  36  of the throttle valve device  34  is slightly inclined to a horizontal plane. Therefore, water does not collect in the bearing parts in which the valve shaft  36  of the throttle valve device  34  is supported and hence the throttle valve device  34  can be lightly operated. 
     The valve shaft  36  is inclined at an angle to a horizontal plane such that its front end is at a level higher than that of its rear end. Therefore, the operating lever  38  does not come into contact with the crankcase  11  when the valve shaft  36  is turned by the throttle valve operating mechanism  40  even though the operating lever  38  is disposed close to the front surface of the crankcase  11  of the internal combustion engine  10 . Since the front surface of the throttle position sensor  57  is substantially parallel to the front wall of the engine cover  6  and a narrow gap is formed between the throttle position sensor  57  and the engine cover  6 , the internal combustion engine  10  and the throttle valve device  34  can be neatly arranged inside the engine cover  6 . 
     In the outboard engine  1  having the crankcase  11  disposed in the front part thereof and the cylinder head  13  disposed in the rear part thereof, the throttle valve device  34  is disposed in front of the crankcase  11 , intake air flows from the left side (right side, as viewed in  FIG. 2 ) of the outboard engine  1  through the throttle valve device  34  rightward, and the upstream end of the throttle valve device  34  is connected to the intake ports  18  formed in the cylinder head  13  by the intake manifold  23  as shown in  FIG. 2 . Therefore, the intake manifold can be formed in a very long length and hence the intake efficiency of the internal combustion engine  10  can be improved. 
     Although there has been described what is the present embodiment of the invention, it will be understood by persons skilled in the art that variations and modifications may be made thereto without departing from the spirit or essence of the invention. The scope of the invention is indicated by the appended claims.