Patent Publication Number: US-6708659-B2

Title: Four cycle engine for marine drive

Description:
PRIORITY INFORMATION 
     This application is based on and claims priority to Japanese Patent Application No. 2001-223982, filed Jul. 25, 2001, the entire contents of which is hereby expressly incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a four-cycle engine for a marine drive, and more particularly to a four-cycle engine for a marine drive that has a vertically extending camshaft. 
     2. Description of Related Art 
     Marine drives such as an outboard motors include a marine propulsion device powered by an engine. The propulsion device typically is a propeller and is submerged when an associated watercraft rests on a body of water. The outboard motor can employ either a two-cycle engine or a four-cycle engine. Recently, however, many outboard motors have been offered with four-cycle engines because they provide better emissions control. 
     Typically, a four-cycle engine includes one or more intake and exhaust valves moving between an open position and a closed position within a cylinder head member. One or more camshafts can be provided to actuate the valves in a timed manner. When the intake valves are open, air is introduced into combustion chambers of the engine through the intake ports. When the exhaust valves are open, exhaust gases are discharged from the combustion chambers through the exhaust ports. 
     The camshafts typically extend vertically within the engine of an outboard motor. The camshafts are driven by a crankshaft of the engine which also extends vertically. The camshafts and the crankshaft can be provided with sprockets or pulleys around which a timing chain or belt is wound so that the crankshaft drives the camshafts through the timing chain or belt. 
     The camshafts can be disposed within a single camshaft chamber or separate camshaft chambers. A camshaft cover member or members together with the cylinder head member define the chamber or chambers. Normally, some lubricant oil collects in the camshaft chambers after lubricating other engine portions. 
     During certain maintenance and repair procedures, the sprockets or pulleys need to be removed from the camshafts and then re-attached afterwards. However, during such procedures, the camshafts should be prevented from rotating. Thus, the camshaft cover member typically is disconnected from the cylinder head member so a tool can be connected to the camshaft so as to prevent rotation thereof. Accordingly, the oil within the camshaft chambers can spill out when the covers are removed, and thereby stain the engine. Thus, the repairperson should pay special attention not to stain the engine with the oil. 
     Additionally, in some arrangements, the camshaft cover member can be nested in a space defined between the sprocket or pulley and the camshaft so as to shorten the outboard motor in height. If the camshaft cover member is necessary to be removed in this arrangement, the sprocket or pulley should be disassembled first. The camshaft is required not to rotate for the disassembling service of the sprocket or pulley. For instance, the timing chain or belt can be fixed by a certain tool so that the camshaft does not rotate. However, the service is extremely difficult because the outboard motor can only afford a limited space for the service. 
     SUMMARY OF THE INVENTION 
     A need therefore exists for an improved four-cycle engine for a marine drive that can provide good serviceability of a camshaft and/or components around the camshaft. 
     In accordance with one aspect of the present invention, an internal combustion engine for a marine drive comprises an engine body. A movable member is movable relative to the engine body. The engine body and the movable member together define a combustion chamber. The engine body defines intake and exhaust ports communicating with the combustion chamber. An air induction system communicates with the combustion chamber through the intake port. An exhaust system communicates with the combustion chamber through the exhaust port. An intake valve is arranged to move between an open position and a closed position. An exhaust valve is arranged to move between an open position and a closed position. A camshaft is configured to actuate either the intake valve or the exhaust valve. The camshaft extends generally vertically. A member is arranged to enclose the camshaft together with the engine body. The member defines an opening through which a tool is capable to pass. The tool is adapted to prevent the camshaft from rotating. 
     In accordance with another aspect of the present invention, a marine drive comprises an internal combustion engine. A cowling assembly is configured to surround the engine. The engine comprises an engine body. A movable member is movable relative to the engine body. The engine body and the movable member together define a combustion chamber. The engine body defines intake and exhaust ports communicating with the combustion chamber. An air induction system communicates with the combustion chamber through the intake port. An exhaust system communicates with the combustion chamber through the exhaust port. An intake valve is arranged to move between an open position and a closed position. An exhaust valve is arranged to move between an open position and a closed position. A camshaft is configured to actuate either the intake valve or the exhaust valve. The camshaft extends generally vertically. A member is arranged to enclose the camshaft together with the engine body. The member defines an opening. The cowling assembly comprises top and bottom cowling members. The top cowling member is detachably coupled with the bottom cowling member. The opening is disposed above a top end of the bottom cowling member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects and advantages of the present invention are described below with reference to the drawings of several preferred embodiments, which are intended to illustrate and not to limit the invention. The drawings comprise eleven figures. 
     FIG. 1 is a side elevational view of an outboard motor configured in accordance with a preferred embodiment of the present invention. An engine and drive train are illustrated in phantom. 
     FIG. 2 is an enlarged partial sectional and port side elevational view of a power head of the outboard motor. A camshaft drive mechanism is omitted in this figure except for an intake camshaft sprocket. 
     FIG. 3 is a top plan view of the power head. A cowling assembly is shown in section. The engine is partially illustrated in section. 
     FIG. 4 is a rear elevational view of the power head. The cowling assembly is shown in section. 
     FIG. 5 is an enlarged, partial sectional and top plan view of the engine illustrating part of an intake system, part of a fuel injection system and a fuel pump assembly of the fuel injection system. 
     FIG. 6 is an enlarged, partial sectional and side elevational view of the engine illustrating a VVT mechanism thereof. 
     FIG. 7 is a sectional view of the VVT mechanism taken along the line  7 — 7  of FIG.  6 . 
     FIG. 8 is a sectional view of the VVT mechanism taken partially along the line  8 — 8  of FIG.  6 . 
     FIG. 9 is a schematic view of a control system of the VVT mechanism. 
     FIG. 10 is an enlarged, partial sectional and top plan view of the engine illustrating an arrangement of a camshaft angle position sensor. 
     FIG. 11 is an enlarged, partial sectional and top plan view of the engine illustrating a preferred arrangement of a maintenance service slot. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     With reference to FIGS. 1-6, an overall construction of an outboard motor  30  that employs an internal combustion engine  32  configured in accordance with certain features, aspects and advantages of the present invention is described below. The engine  32  has particular utility in the context of a marine drive, such as the outboard motor, and thus is described in the context of an outboard motor. The engine  32 , however, can be used with other types of marine drives (i.e., inboard motors, inboard/outboard motors, jet drives, etc.) and also certain land vehicles. In any of these applications, the engine  32  can be oriented vertically or horizontally. Furthermore, the engine  32  can be used as a stationary engine for some applications as is apparent to those of ordinary skill in the art in light of the description herein. 
     The outboard motor  30  generally comprises a drive unit  34 , a bracket assembly  36 , and a marine propulsion device  41 . The bracket assembly  36  supports the drive unit  34  on a transom  38  of an associated watercraft  40  and places the marine propulsion device  41  in a submerged position when the watercraft  40  rests on a surface of a body of water WL. The bracket assembly  36  preferably comprises a swivel bracket  42 , a clamping bracket  44 , a steering shaft and a pivot pin  46 . 
     The steering shaft typically extends through the swivel bracket  42  and is affixed to the drive unit  34  by top and bottom mount assemblies  43 . The steering shaft is pivotally journaled for steering movement about a generally vertically extending steering axis defined within the swivel bracket  42 . The clamping bracket  44  comprises a pair of bracket arms that are spaced apart from each other and that are affixed to the watercraft transom  38 . The pivot pin  46  completes a hinge coupling between the swivel bracket  42  and the clamping bracket  44 . The pivot pin  46  extends through the bracket arms so that the clamping bracket  44  supports the swivel bracket  42  for pivotal movement about a generally horizontally extending tilt axis defined by the pivot pin  46 . The drive unit  34  thus can be tilted or trimmed about the pivot pin  46 . 
     As used through this description, the terms “forward,” “forwardly” and “front” mean at or toward the side where the bracket assembly  36  is located, and the terms “rear,” “reverse,” “backwardly” and “rearwardly” mean at or toward the opposite side of the front side, unless indicated otherwise or otherwise readily apparent from the context use. 
     A hydraulic tilt and trim adjustment system  48  preferably is provided between the swivel bracket  42  and the clamping bracket  44  for tilt movement (raising or lowering) of the swivel bracket  42  and the drive unit  34  relative to the clamping bracket  44 . Otherwise, the outboard motor  30  can have a manually operated system for tilting the drive unit  34 . Typically, the term “tilt movement”, when used in a broad sense, comprises both a tilt movement and a trim adjustment movement. 
     The illustrated drive unit  34  comprises a power head  50  and a housing unit  52 . The housing unit  52  includes a driveshaft housing  54  and a lower unit  56 . The power head  50  is disposed atop the drive unit  34  and includes the internal combustion engine  32  and a protective cowling assembly  60 . 
     Preferably the protective cowling  60  is made of plastic and defines a generally closed cavity  62  (FIGS. 2-4) in which the engine  32  is disposed. That is, the cowling assembly  60  surrounds the engine  32 . The protective cowling assembly  60  preferably comprises a top cowling member  64  and a bottom cowling member  66 . The top cowling member  64  preferably is detachably affixed to the bottom cowling member  66  by a coupling mechanism  68 . When the top cowling member  64  is detached, a user, operator, mechanic or repairperson can access the engine  32  for maintenance or for other purposes. 
     With reference to FIG. 2, the top cowling member  64  preferably has a rear intake opening  72  on its rear and top portion. A rear intake member  74  with a rear air duct  76  is affixed to the top cowling member  64 . The rear intake member  74 , together with the rear top portion of the top cowling member  64 , forms a rear air intake space  78 . With particular reference to FIG. 4, the rear air duct  76  preferably is disposed to the starboard side of a central portion of the rear intake member  74 . 
     With reference to FIG. 2, the top cowling member  64  also defines a recessed portion  82  at a front end thereof An opening  84  is defined along a portion of the recessed portion  82  on the starboard side. The opening  84  extends into the interior of the top cowling member  64 . An outer shell  86  is disposed over the recessed portion  82  to define a front air intake space  88 . A front air duct  90  is affixed to the recessed portion  82  of the top cowling member  64  and extends upward from the opening  84 . In this manner, the air flow path into the closed cavity  62  can include an elevated entrance from the front air intake space  88 . The air duct  90  preferably has a plurality of apertures  92 , each of which preferably is cylindrical. 
     A front intake opening (not shown) preferably is defined between the recessed portion  82  of the top cowling member  82  and the outer shell  86  so that the front intake space  88  communicates with outside of the cowling assembly  60 . Ambient air thus is drawn into the closed cavity  62  through the rear intake opening  72  or the front intake opening (not shown) and further through the air ducts  76 ,  90 . Typically, the top cowling member  64  tapers in girth toward its top surface, which is in the general proximity of the air intake opening  72 . 
     The bottom cowling member  66  preferably has an opening  96  (FIG. 2) through which an upper portion of an exhaust guide member  98  (FIG. 1) extends. The exhaust guide member  98  preferably is made of aluminum alloy and is affixed atop the driveshaft housing  54 . The bottom cowling member  66  and the exhaust guide member  98  together generally form a tray. The engine  32  is placed onto this tray and is affixed to the exhaust guide member  98 . The exhaust guide member  98  also has an exhaust passage through which burnt charges (e.g., exhaust gases) from the engine  32  are discharged. 
     With reference to FIGS. 2-5, the engine  32  in the illustrated embodiment preferably operates on a four-cycle combustion principle. The engine  32  has a cylinder block  102 . The presently preferred cylinder block  102  defines four in-line cylinder bores  104  which extend generally horizontally and which are generally vertically spaced from one another. As used in this description, the term “horizontally” means that the subject portions, members or components extend generally in parallel to the water line WL when the associated watercraft  40  is substantially stationary with respect to the water line WL and when the drive unit  34  is not tilted and is placed in the position shown in FIG.  1 . The term “vertically” in turn means that portions, members or components extend generally normal to those that extend horizontally. 
     This type of engine, however, merely exemplifies one type of engine on which various aspects and features of the present invention can be suitably used. Engines having other numbers of cylinders and having other cylinder arrangements (V, W, opposing, etc.) also can employ various features, aspects and advantages of the present invention. In addition, the engine can be formed with separate cylinder bodies rather than a number of cylinder bores formed in a cylinder block. Regardless of the particular construction, the engine preferably comprises an engine body that includes at least one cylinder bore  104 . 
     A moveable member, such as a reciprocating piston  106 , moves relative to the cylinder block  102  in a suitable manner. One piston  106  reciprocates within each cylinder bore  104 . 
     A cylinder head member  108  is affixed to one end of the cylinder block  102  to close one end of the cylinder bores  104 . The cylinder head member  108 , together with the associated pistons  106  and cylinder bores  104 , preferably defines four combustion chambers  110 . Of course, the number of combustion chambers can vary, as indicated above. 
     A crankcase member  112  closes the other end of the cylinder bores  104  and, together with the cylinder block  102 , defines a crankcase chamber  114 . A crankshaft or output shaft  118  extends generally vertically through the crankcase chamber  114  and can be journaled for rotation by several bearing blocks (not shown). A center vertical plane VP FIG. 3) of the outboard motor  30  extends generally vertically and fore to aft through the cylinder block  102 , the cylinder head member  108 , and the crankcase member  112 . The verticle plane VP preferably includes a longitudinal axis of the crankshaft  118 . Connecting rods  120  couple the crankshaft  118  with the respective pistons  106  in any suitable manner. Thus, the crankshaft  118  can rotate with the reciprocal movement of the pistons  106 . 
     Preferably, the crankcase member  112  is located at the forward-most position of the engine  32 , with the cylinder block  102  and the cylinder head member  108  being disposed rearward from the crankcase member  112 . Generally, the cylinder block  102  (or individual cylinder bodies), the cylinder head member  108 , and the crankcase member  112  together define an engine body  124 . Preferably, at least these major engine portions  102 ,  108 ,  112  are made of an aluminum alloy. The aluminum alloy advantageously increases strength over cast iron while decreasing the weight of the engine body  124 . 
     The engine  32  also comprises an air induction system or device  126 . The air induction system  126  draws air from within the cavity  62  to the combustion chambers  110 . The air induction system  126  preferably comprises eight intake ports  128 , four intake passages  130  and a single plenum chamber  132 . In the illustrated arrangement, two intake ports  128  are allotted to each combustion chamber  110  and the two intake ports  128  communicate with a single intake passage  130 . 
     The intake ports  128  are defined in the cylinder head member  108 . Intake valves  134  are slidably disposed at the intake ports  128  within the cylinder head member  108  to move between an open position and a closed position. As such, the valves  134  act to open and close the ports  128  to control the flow of air into the combustion chamber  110 . 
     Biasing members, such as springs  136  (FIGS.  5  and  6 ), are used to bias the intake valves  134  toward the respective closed positions by acting against a mounting boss formed on the illustrated cylinder head member  108  and a corresponding retainer  138  that is affixed to each of the valves  134 . When each intake valve  134  is in the open position, the intake passage  130  that is associated with the intake port  128  communicates with the associated combustion chamber  110 . 
     With reference to FIGS. 3 and 5, each intake passage  130  preferably is defined by an intake manifold  140 , a throttle body  142  and an intake runner  144 . The intake manifold  140  and the throttle body  142  preferably are made of aluminum alloy. The intake runner  144  preferably is made of plastic. A portion of the illustrated intake runner  144  extends forwardly alongside of and to the front of the crankcase member  112 . 
     With continued reference to FIG. 3, the respective portions of the intake runners  144 , together with a plenum chamber member  146 , define the plenum chamber  132 . Preferably, the plenum chamber member  146  also is made of plastic. 
     The plenum chamber  132  comprises an air inlet  148 . The air in the cavity  62  is drawn into the plenum chamber  132  through the air inlet  148 . The air is then passed through intake passages  130 , the throttle body  142  and the intake manifold  140 . Preferably, the plenum chamber  132  is configured to attenuate noise generated by the flow of air into the respective combustion chambers  110 , and thus act as an “intake silencer.” 
     Each illustrated throttle body  142  includes a butterfly type throttle valve  152  journaled for pivotal movement about an axis defined by a generally vertically extending valve shaft  154 . Each valve shaft  154  can be coupled with the other valve shafts to allow simultaneous movement. The valve shaft  154  is operable by the operator through an appropriate conventional throttle valve linkage and a throttle lever connected to the end of the linkage. The throttle valves  152  are movable between an open position and a closed position to meter or regulate an amount of air flowing through the respective air intake passages  130 . Normally, the greater the opening degree, the higher the rate of airflow and the higher the power output of the engine. 
     In order to bring the engine  32  to idle speed and to maintain this speed, the throttle valves  152  generally are substantially closed. Preferably, the valves are not fully closed in the idle position so as to produce a more stable idle speed and to prevent sticking of the throttle valves  152  in the closed position. As used through the description, the term “idle speed” generally means a low engine speed that achieved when the throttle valves  152  are closed but also includes a state such that the valves  152  are slightly more open to allow a relatively small amount of air to flow through the intake passages  130 . 
     The air induction system  126  preferably includes an auxiliary air device (AAD) (not shown) that bypasses the throttle valves  152  and extends from the plenum chamber  132  to the respective intake passages  130  downstream of the throttle valves  152 . Auxiliary air, primarily idle air, can be delivered to the combustion chambers  110  through the AAD when the throttle valves  152  are placed in a substantially closed or closed position. 
     The AAD preferably comprises an auxiliary air passage, an auxiliary valve and an auxiliary valve actuator. The auxiliary air passage is branched off to the respective intake passages  130 . The auxiliary valve controls flow through the auxiliary air passage such that the amount of air flow can be more precisely controlled. Preferably, the auxiliary valve is a needle valve that can move between an open position and a closed position, which closes the auxiliary air passage. The auxiliary valve actuator actuates the auxiliary valve to meter or adjust an amount of the auxiliary air. 
     The engine  32  also comprises an exhaust system that guides burnt charges, i.e., exhaust gases, to a location outside of the outboard motor  30 . Each cylinder bore  104  preferably has two exhaust ports (not shown) defined in the cylinder head member  108 . The exhaust ports can be selectively opened and closed by exhaust valves. The exhaust valves are schematically illustrated in FIG. 9, described below, and are identified by reference numeral  156 . The construction of each exhaust valve and the arrangement of the exhaust valves are substantially the same as the intake valves  134  and the arrangement thereof, respectively. 
     An exhaust manifold (not shown) preferably is disposed next to the exhaust ports (not shown) and extends generally vertically. The exhaust manifold communicates with the combustion chambers  110  through the exhaust ports to collect exhaust gases therefrom. The exhaust manifold is coupled with the exhaust passage of the exhaust guide member  98 . When the exhaust ports are opened, the combustion chambers  110  communicate with the exhaust passage through the exhaust manifold. 
     With particular reference to FIGS. 2,  3 ,  5 ,  6  and  8 , a valve cam mechanism or valve actuator  170  preferably is provided for actuating the intake valves  134  and the exhaust valves  156  (FIG.  9 ). In the illustrated arrangement, the valve cam mechanism  170  includes an intake camshaft  172  and an exhaust camshaft  174  both extending generally vertically and journaled for rotation relative to the cylinder head member  108 . In the illustrated arrangement, bearing caps  176 ,  178  (FIG. 2) journal the camshafts  172 ,  174  with the cylinder head member  108 . 
     A camshaft cover member  179  is affixed to the cylinder head member  108  by bolts  568  (FIG. 8) via a seal member  570  made of, for example, rubber to define a pair of camshaft chambers  180  together with the cylinder head member  108 . The seal member  570  not only seals but also prevents the camshaft cover member  179  from vibrating. As shown in FIG. 8, at least a portion  572  of the camshaft cover member  179  abuts the cylinder head member  108  without interposing the seal member  570 . This is advantageous because the camshaft cover member  179  is accurately positioned relative to the cylinder head member  108 . Each camshaft  172 ,  174  is enclosed within each camshaft chamber  180 . Alternatively, separate camshaft cover members can replace the single cover member  180  to separately enclose the camshafts  172 ,  174 . 
     Each camshaft  172 ,  174 , as shown in FIG. 6, has a plurality of cams  181  associated with the intake or exhaust valves  134 ,  156 . Each cam  181  defines a cam lobe  181   a  to push valve lifters  182  that are affixed to the respective ends of the intake valves  134  and exhaust valves  156  (FIG. 9) as in any suitable manner. The cam lobes  181   a  repeatedly push the valve lifters  182  in a timed manner, which is in proportion to the engine speed. The movement of the lifters  182  generally is timed by the rotation of the camshafts  172 ,  174  to actuate the intake valves  134  and the exhaust valves. 
     As shown in FIG. 6, in the illustrated arrangement, a top end of the camshaft cover member  179  is nested between an inner surface of the sprocket  188  and an outer surface of a top end of the cylinder block  108 . Thus, the camshaft cover member  179  is attached to or detached from the intake camshaft  172  with the sprocket  188  removed. This arrangement allows the total height of the engine  32  to be shorter. 
     With reference to FIG. 3, a camshaft drive mechanism  186  drives the valve cam mechanism  170 . The intake camshaft  172  and the exhaust camshaft  174  include an intake driven sprocket  188  positioned atop the intake camshaft  172  and an exhaust driven sprocket  190  positioned atop the exhaust camshaft  174 . The crankshaft  118  has a drive sprocket  192  positioned at an upper portion thereof. Of course, other locations of the sprockets also can be used. The illustrated arrangement, however, advantageously results in a compactly arranged engine. 
     A timing chain or belt  194  is wound around the driven sprockets  188 ,  190  and the drive sprocket  192 . The crankshaft  118  thus drives the respective camshafts  172 ,  174  through the timing chain  194  in the timed relationship. Because the camshafts  172 ,  174  must rotate at half of the speed of the rotation of the crankshaft  118  in the four-cycle combustion principle, a diameter of the driven sprockets  188 ,  190  is twice as large as a diameter of the drive sprocket  192 . 
     With reference to FIGS. 3-5, the engine  32  preferably has a port or manifold fuel injection system. The fuel injection system preferably comprises four fuel injectors  198  with one fuel injector allotted for each of the respective combustion chambers  110  through suitable fuel conduits. Each fuel injector  198  preferably has an injection nozzle directed toward the associated intake passage  130  adjacent to the intake ports  128 . The fuel injectors  198  preferably are mounted on a fuel rail  199 . Preferably, the fuel rail  199  extends generally vertically and is mounted on the intake manifolds  140 . The fuel rail  199  also defines a portion of the fuel conduits. 
     A heat exchanger  200  preferably is provided to cool the fuel and extends parallel to the fuel rail  199 . The heat exchanger  200  preferably comprises a pair of fluid pipes, one of which defines part of the fuel conduits and the other defines a water passage through which cooling water can flow. 
     With reference to FIGS. 4 and 5, the illustrated fuel injection system additionally comprises a fuel pump assembly  500  that is actuated by the intake camshaft  172 . The fuel pump assembly  500  is mounted on the camshaft cover member  179  and is disposed adjacent to the intake cam  181  that actuates the intake valve  134  associated with the combustion chamber  110  positioned second from the bottom. 
     The fuel pump assembly  500  preferably comprises a bottom housing member  502 , a middle housing member  504  and a top housing member  506 . The housing members  502 ,  504 ,  506  are coupled together by bolts  508 . The bottom housing member  502  forms a projection  510 . The camshaft cover member  179  defines an opening at a support portion  512  thereof and the projection  510  is fitted into the opening so that the fuel pump assembly  500  is mounted on the cover member  179 . Fasteners such as bolts can fix the pump assembly  500  to the cover member  179 . 
     A diaphragm  516  preferably is provided with a periphery portion thereof interposed between the bottom and middle housing members  502 ,  504 . A pump rod  518  depends from the diaphragm  516 . A top portion  520  of the pump rod  518  preferably supports upper and lower plates  524 ,  526  which together sandwich the diaphragm  516  therebetween. The bottom housing member  502  defines a guide section  530  that slidably supports the top portion  520  of the pump rod  520 . A spring  532  urges the diaphragm  516  upwardly such that the lower plate  526  does not abut the guide section  530 . The guide section  530  and the projection  510  together define a recess in which a slider  534  slides. A spring  536  biases the slider  534  downwardly. The slider  534  defines a recess therein in which a lower portion of the pump rod  520  slides. A lowermost end  538  of the slider  534  protrudes downwardly. 
     An arm member  540  is journaled on a support shaft  542  for pivotal movement about an axis of the shaft  542 . The support shaft  542  is affixed to the bearing cap  178 . The lowermost end  538  of the slider  534  is biased against a top surface of the arm member  540  by the spring  536 . The arm member is thereby biased against the cam  181 . The cam  181  thus lifts the slider  534  upwardly when the cam lobe  181  a meets the arm member  540 . 
     The diaphragm  516  defines a pump chamber  546  together with the middle housing member  504 . The middle housing member  504  and the top housing member  506  in turn together define an inlet chamber  548  and an outlet chamber  550  both of which are separated from each other. The inlet chamber  548  is connected toward a fuel source such as, for example, a fuel tank, while the outlet chamber  550  is connected toward the fuel rail  199 . The inlet chamber  548  also is connected to the pump chamber  546  through an inlet path member  552  fitted into an aperture communicating with both the inlet and pump chambers  548 ,  546 . The outlet chamber  550  also is connected to the pump chamber  546  through an outlet path member  554  fitted into an aperture communicating with both the outlet and pump chambers  550 ,  546 . 
     One end of the inlet path member  552  is open to the inlet chamber  548  and another end thereof is closed but one or a plurality of side openings are formed in close proximity to this end to communicate with the pump chamber  546 . A flange  558  is provided adjacent to the side openings so as to somewhat impede fuel from moving to the pump chamber  546 . Similarly, one end of the outlet path member  554  is open to the pump chamber  546  and another end thereof is closed but one or more side openings are formed in close proximity to this end to communicate with the outlet chamber  550 . A flange  560  is provided adjacent to the side openings so as to somewhat impede fuel from moving to the outlet chamber  550 . 
     With the intake camshaft  172  rotating, the cam  181  lifts the arm member  540  at every moment when the cam lobe  181  a meets the arm member  540 . The arm member  540  thus repeatedly pivots about the axis of the support shaft  542  and reciprocally moves the slider  534  together with the spring  536 . The slider  534  pushes the pump rod  518  upwardly when the slider  534  moves upwardly and releases the pump rod  518  when the slider  534  moves downwardly so that the pump rod  518  also repeatedly moves upwardly and downwardly. The diaphragm  516 , which is affixed to the top portion  520  of the pump rod  518 , thus move upwardly and downwardly. The volume of the pump chamber  546  thus is repeatedly changed. Accordingly, the fuel in the pump chamber  546  moves into the outlet chamber  550  through the outlet path member  554  and the fuel in the inlet chamber  548  moves into the pump chamber  546  through the inlet path member  552 . The fuel pump  500  thus can deliver the fuel from the fuel tank to the fuel rail  199 . 
     The fuel injectors  198  spray fuel into the intake passages  130  under control of an ECU  201  (FIG. 9) which preferably is mounted on the engine body  124  at an appropriate location. The ECU  201  controls both the start timing and the duration of the fuel injection cycle of the fuel injectors  198  so that the nozzles spray a proper amount of the fuel for each combustion cycle. The fuel injection controller within the ECU  201  is illustrated in FIG. 9 with reference numeral  202  and is described below. Of course, the fuel injectors  198  can be disposed for direct cylinder injection and carburetors can replace or accompany the fuel injectors  198 . 
     With reference to FIGS. 2 and 4, the engine  32  further comprises an ignition or firing system. Each combustion chamber  110  is provided with a spark plug  203  that is connected to the ECU  201  (FIG. 9) through an igniter so that ignition timing is also controlled by the ECU  201 . Each spark plug  203  has electrodes that are exposed into the associated combustion chamber and are spaced apart from each other with a small gap. The spark plugs  203  generate a spark between the electrodes to ignite an air/fuel charge in the combustion chamber  110  at selected ignition timing under control of the ECU  201 . 
     In the illustrated engine  32 , the pistons  106  reciprocate between top dead center and bottom dead center. When the crankshaft  118  makes two rotations, the pistons  106  generally move from the top dead center to the bottom dead center (the intake stroke), from the bottom dead center to the top dead center (the compression stroke), from the top dead center to the bottom dead center (the power stroke) and from the bottom dead center to the top dead center (the exhaust stroke). During the four strokes of the pistons  106 , the camshafts  172 ,  174  make one rotation and actuate the intake valves  134  and the exhaust valves  156  (FIG. 9) to open the intake ports  128  during the intake stroke and to open exhaust ports during the exhaust stroke, respectively. 
     Generally, during the intake stroke, air is drawn into the combustion chambers  110  through the air intake passages  130  and fuel is injected into the intake passages  130  by the fuel injectors  198 . The air and the fuel thus are mixed to form the air/fuel charge in the combustion chambers  110 . Slightly before or during the power stroke, the respective spark plugs  203  ignite the compressed air/fuel charge in the respective combustion chambers  110 . The air/fuel charge thus rapidly burns during the power stroke to move the pistons  106 . The burnt charge, i.e., exhaust gases, then are discharged from the combustion chambers  110  during the exhaust stroke. 
     During engine operation, heat builds in the engine body  124 . The illustrated engine  32  thus includes a cooling system to cool the engine body  124 . The outboard motor  30  preferably employs an open-loop type water cooling system that introduces cooling water from the body of water surrounding the motor  30  and then discharges the water to the body of water. The cooling system includes one or more water jackets defined within the engine body  124  through which the water travels to remove heat from the engine body  124 . The foregoing heat exchanger  200  can use part of the water flowing through the cooling system. 
     The engine  32  also preferably includes a lubrication system. A closed-loop type system preferably is employed in the illustrated embodiment. The lubrication system comprises a lubricant tank defining a reservoir, which preferably is positioned within the driveshaft housing  54 . An oil pump (not shown) is provided at a desired location, such as atop the driveshaft housing  54 , to pressurize the lubricant oil in the reservoir and to pass the lubricant oil through a suction pipe toward certain engine portions, which desirably are lubricated, through lubricant delivery passages. The engine portions that need lubrication include, for example, the crankshaft bearings (not shown), the connecting rods  120  and the pistons  106 . Portions  214  of the delivery passages (FIG. 2) can be defined in the crankshaft  118 . Lubricant return passages (not shown) also are provided to return the oil to the lubricant tank for re-circulation. 
     A flywheel assembly  216  (FIG. 2) preferably is positioned at an upper end of the crankshaft  118  and is mounted for rotation with the crankshaft  118 . The flywheel assembly  216  comprises a flywheel magneto or AC generator that supplies electric power to various electrical components such as the fuel injection system, the ignition system and the ECU  201  (FIG.  9 ). A protective cover  218 , which preferably is made of plastic, extends over majority of the top surface of the engine  32  and preferably covers the portion that includes the fly wheel assembly  216  and the camshaft drive mechanism  186 . 
     The protective cover  218  preferably has a rib  219  (FIG. 4) that reduces or eliminates the amount of air flowing directly toward the engine portion that has the air induction system  126 , i.e., to the portion on the starboard side. The protective cover  218  also preferably has a rib  220  (FIG. 2) that substantially or completely inhibits air from flowing directly toward a front portion of the engine body  124 . The ribs  219 ,  222  advantageously help direct the airflow around the engine body  124  to cool the engine body  124 . As seen in FIG. 2, a bottom portion, at least in part, of the protective cover  218  desirably is left open to allow heat to radiate from the engine  32 . 
     With reference to FIG. 1, the driveshaft housing  54  depends from the power head  50  to support a driveshaft  222  which is coupled with the crankshaft  118  and which extends generally vertically through the driveshaft housing  54 . The driveshaft  222  is journaled for rotation and is driven by the crankshaft  118 . The driveshaft housing  54  preferably defines an internal section of the exhaust system that leads the majority of exhaust gases to the lower unit  56 . An idle discharge section is branched off from the internal section to discharge idle exhaust gases directly out to the atmosphere through a discharge port that is formed on a rear surface of the driveshaft housing  54  in idle speed of the engine  32 . The driveshaft  222  preferably drives the oil pump. 
     With continued reference to FIG. 1, the lower unit  56  depends from the driveshaft housing  54  and supports a propulsion shaft  226  that is driven by the driveshaft  222 . The propulsion shaft  226  extends generally horizontally through the lower unit  56  and is journaled for rotation. The propulsion device  41  is attached to the propulsion shaft  226 . In the illustrated arrangement, the propulsion device includes a propeller  228  that is affixed to an outer end of the propulsion shaft  226 . The propulsion device, however, can take the form of a dual counter-rotating system, a hydrodynamic jet, or any of a number of other suitable propulsion devices. 
     A transmission  232  preferably is provided between the driveshaft  222  and the propulsion shaft  226 , which lie generally normal to each other (i.e., at a 90° shaft angle) to couple together the two shafts  222 ,  226  by bevel gears. The transmission  232  includes a switchover mechanism (not shown) that is configured to change a rotational direction of the propeller  228  between forward, neutral or reverse. The switchover mechanism typically comprises a dog clutch and a shift unit that operates the dog clutch. At the forward and reverse positions, which are propulsion positions, the propeller  228  propels the watercraft  40  forward and backward, respectively. At the neutral position, which is a-non-propulsion position, the propeller  228  does not propel the watercraft  40  because the propulsion shaft  226  is disconnected from the driveshaft  222 . 
     Preferably, the switchover mechanism is interconnected with the throttle valve linkage. A single control lever, which is the foregoing throttle lever, is connected with not only the throttle valve but also the switchover mechanism to control both of them in an interrelationship such that the throttle valve is always closed (or almost closed) when the transmission is placed in the neutral position by the switchover mechanism, except for an engine racing operation. The throttle linkage can be released from the switchover mechanism for the racing operation. 
     The lower unit  56  also defines an internal section of the exhaust system that is connected with the internal section of the driveshaft housing  54 . At engine speeds above idle, the exhaust gases generally are discharged to the body of water surrounding the outboard motor  30  through the internal sections and then through a discharge section defined within the hub of the propeller  228 . Preferably, the outboard motor  30  also includes an idle exhaust discharge (not shown) configured to discharge exhaust gases to the atmosphere at a position above the waterline WL at idle engine speeds. 
     VVT Mechanism 
     With reference to FIGS. 2-4,  6  and  8  and with additional reference to FIG. 7, a VVT mechanism  240  is described below. 
     The VVT mechanism  240  preferably is configured to adjust the angular position of the intake camshaft  172  relative to the intake driven sprocket  188  between two limits, i.e., a fully advanced angular position and a fully retarded angular position. At the fully advanced angular position, the intake camshaft  172  opens and closes the intake valves  134  at a most advanced timing. In contrast, at the fully retarded angular position, the intake camshaft  172  opens and closes the intake valves  134  at a most retarded timing. 
     The VVT mechanism  240  preferably is hydraulically operated and thus comprises an adjusting section  242 , a fluid supply section  244  and a control section  246 . The adjusting section  242  sets the intake camshaft  172  to an angular position in response to a volume of working fluid that is allotted to two spaces of the adjusting section  242 . The fluid supply section  244  preferably supplies a portion of the lubricant, which is used primarily for the lubrication system, to the adjusting section  242  as the working fluid. The control section  246  selects the rate or amount of the fluid directed to the adjusting section  242  under control of the ECU  201  (FIG.  9 ). 
     With reference to FIG. 7, the adjusting section  242  preferably includes an outer housing  250  and an inner rotor  252 . The outer housing  250  is affixed to the intake driven sprocket  188  by three bolts  254  in the illustrated arrangement and preferably forms three hydraulic chambers  256  between the three bolts  254 . Any other suitable fastening technique and any suitable number of chambers  256  can be used. 
     The inner rotor  252  is affixed atop the intake camshaft  172  by a bolt  258  (FIG. 6) and has three vanes  260  extending into the respective chambers  256  of the housing  250 . The number of vanes  260  can be varied and the inner rotor  252  can be attached to the camshaft  172  in any suitable manners. 
     With reference to FIG. 7, the vanes  260  preferably extend radially and are spaced apart from each other with an angle of about 120 degrees. The two sides of the vane  260 , together with walls  262  of each chamber  256 , define a first space S 1  and a second space S 2 , respectively. Seal members  266  carried by the respective vanes  260  abuts an inner surface of the housing  250  and thereby substantially seal the first and second spaces S 1 , S 2  from each other. 
     The respective first spaces S 1  communicate with one another through respective pathways  270  and a passage  272  that is formed on an upper surface of the rotor  252  and extends partially around the bolt  258 . The respective second spaces S 2  communicate with one another through respective pathways  274  and a passage  276  which is formed on a lower surface of the rotor  252  and extends partially around the bolt  258 . The passages  272 ,  276  generally are configured as an incomplete circular shape and can be offset from one another (e.g., a 60 degree offset may be used). 
     A pathway  278  extends from the passage  272  to a bottom portion of the rotor  252  between the ends of the passage  276 . A cover member  280  preferably is affixed to the outer housing  250  by screws  282  to cover the bolt  258 . The cover member  280  preferably is made of rubber, synthetic resin or sheet metal and can be fitted into an aperture  283  without using the screws  282 . The passages  272 ,  276  allow fluid communication with the respective pathways  270 ,  274 ,  278  during rotation of the camshaft  172 . 
     With reference to FIGS. 2 and 6, the fluid supply section  244  preferably includes a supply passage  284  and two delivery passages  286 ,  288 . The supply passage  284  and the delivery passages  286 ,  288  communicate with one another through the control section  246 . The supply passage  284  preferably has a passage portion  284   a  (FIGS. 2 and 6) defined in the cylinder head member  108  and a passage portion  284   b  (FIG. 2) defined in the bearing cap  176 . The passage portion  284   a  is connected to the lubrication system, while the passage portion  284   b  is connected to the control section  246 . Thus, the lubricant oil of the lubrication system is supplied to the control section  246  through the fluid supply passage  284 . 
     The supply passage  284  communicates with the lubrication system so that a portion of the lubricant oil is supplied to the VVT mechanism  240  as working fluid through the passage portions  284   a,    284   b.  Because the passage portion  284   a  is formed by a drilling process in the illustrated embodiment, a closure member  290  closes one end of the passage portion  284   a.  The passage portion  284   b  is branched off to a camshaft lubrication passage  284   c  (FIG. 6) which delivers lubricant for lubrication of a journal of the camshaft  172 . 
     The delivery passages  286 ,  288  preferably are defined in a top portion of the camshaft  172  and the bearing cap  176 . A portion of the delivery passage  286  formed in the camshaft  172  includes a pathway  292  that extends generally vertically and that communicates with the pathway  278  that communicates with the passage  272  of the first space S 1 . The pathway  292  also communicates with a passage  294  that is formed as a recess in the outer surface of the camshaft  172 . 
     A portion of the delivery passage  288  formed in the camshaft  172 , in turn, includes a pathway  296  that extends generally vertically and communicates with the passage  276  of the second space S 2 . The pathway  296  also communicates with a passage  298  that is formed as a recess in the outer surface of the camshaft  172 . 
     A portion of the delivery passage  286  formed in the bearing cap  176  includes a pathway  300  that extends generally vertically and generally horizontally to communicate with the passage  294 . Similarly, a portion of the delivery passage  288  formed in the bearing cap  176  includes a pathway  302  that extends generally vertically and generally horizontally to communicate with the passage  298 . The other ends of the pathways  300 ,  302  communicate with a common chamber  304  formed in the control section  246  through ports  306 ,  308 , respectively. 
     A seal member  310  (FIG. 6) is disposed between the cylinder head member  108 , the camshaft  172  and the bearing cap  176  to inhibit the lubricant from leaking out. It should be noted that FIGS. 6 and 8 illustrate the delivery passages  286 ,  288  in a schematic fashion. The passages  286 ,  288  do not merge together. 
     The control section  246  preferably includes an oil control valve (OCV)  314  (FIG.  8 ). The OCV  314  comprises a housing section  316  and a cylinder section  318 . A lower end  319  (FIG. 4) of the protective cover  218  covers the housing section  316  so that water, if any, does not to splash onto the housing section  316 . Both the housing and cylinder sections  316 ,  318  preferably are received in the bearing cap  176 . Because the sections  316 ,  318  together extend through a hole of the camshaft cover member  179 , a bellow  320  made of rubber is provided between the housing section  316  and the camshaft cover member  179  to close and seal the hole. 
     The cylinder section  318  defines the common chamber  304  that communicates with the supply passage  284  and the delivery passages  286 ,  288 . The housing section  316  preferably encloses a solenoid type actuator, although other actuators of course are available. 
     A rod  324  extends into the common chamber  304  from the actuator and is axially movable therein. The rod  324  has a pair of valves  326 ,  328  and a pair of guide portions  330 . The valves  326 ,  328  and the guide portions  330  have an outer diameter that is larger than an outer diameter of the remainder portions  331  of the rod  324  and is generally equal to an inner diameter of the cylinder section  318 . The rod  324  defines an internal passage  334  extending through the rod  324  and apertures  335  communicating with the passage  334  and the common chamber  304  to allow free flow of the fluid in the chamber  304 . 
     A coil spring  338  is retained in a spring retaining space  339  at an end of the cylinder  318  opposite to the housing section  316  to urge the rod  324  toward the actuator. The fluid can be drained to the camshaft chamber  180  through the spring retaining chamber  339  and a drain hole  340 . 
     The actuator, i.e., solenoid, actuates the rod  324  under control of the ECU  201  (FIG. 9) so that the rod  324  can take any position in the chamber  304 . More specifically, the solenoid pushes the rod  324  toward a position in compliance with commands of the ECU  201 . If a certain position designated by the ECU  201  is closer to the solenoid than a current position, then the solenoid does not actuate the rod  324  and the coil spring  338  pushes the rod  324  back to the desired position. Alternatively, the solenoid can be configured to pull the rod  324  back to the position. 
     The valve  326  can close the port  306  entirely or partially, and the valve  328  can close the port  308  entirely or partially. The size of the openings at the ports  306 ,  308  determines an amount of the fluid that is allotted to each delivery passage  286 ,  288  and to each space S 1 , S 2  in the adjusting section  242 . The amount of fluid delivered to each space S 1 , S 2  thus determines an angular position of the camshaft  172 . If more fluid is allotted to the first space S 1  than to the second space S 2 , the camshaft  172  is adjusted closer to the fully advanced position, and vise versa. 
     The oil pump pressurizes the lubricant oil to the supply passage  284  and further to the common chamber  304  of the cylinder  318 . Meanwhile, the ECU  201  (FIG. 9) controls the solenoid. The solenoid moves the rod  324  and thus adjusts the degree to which the valves  326 ,  328  allow the chamber to communicate with the ports  306 ,  308 , respectively. The ECU  201  thereby controls the angular position of the camshaft  172 . Preferably, a drain is provided to allow the working fluid to drain from the space that is being evacuated while pressurized working fluid flows into the opposing space. 
     In one mode of operation, for example, the working fluid is fed to the common chamber  304  of the cylinder  318 . Thus, the common chamber  304  has a positive pressure. To move the camshaft  172  in a first direction relative to the input sprocket  188 , the common chamber  304  is linked with the delivery passage  286  while the other of the delivery passage  288  is linked to a drain. Thus, pressurized fluid will flow into the first space S 1  while fluid will be displaced from the second space S 2 . The displaced fluid flows through the passage  334  and to the drain  340  and thereby returns to the lubrication system. Once the desired movement has occurred, the rod  324  is returned to a neutral position in which the common chamber  304  is no longer communicating with either of the delivery passages  286 ,  288 . Additionally, in the neutral position, neither of the delivery passages  286 ,  288  communicates with the drain in one particularly advantageous arrangement. Of course, by varying the placement and size of the seals, a constant flow can be produced from supply to drain while the rod  324  is in a neutral position. Also, a constant flow into the delivery lines also can be constructed. In the illustrated arrangement, however, no flow preferably occurs with the system in a neutral position. 
     In general, the engine and the VVT mechanism are disclosed in, for example, a co-pending U.S. application filed Jun. 11, 2001, titled FOUR-CYCLE ENGINE FOR MARINE DRIVE, which Ser. No. is 09/878,323, the entire contents of which is hereby expressly incorporated by reference. 
     With reference to FIGS. 2,  4  and  11 , in the illustrated arrangement, the camshaft cover member  179  preferably defines an access opening  574  below the VVT mechanism  240  and above the fuel pump assembly  500 . Preferably, the opening  574  is disposed above the top end  70  of the bottom cowling member  66 . A closure member  576  is detachably affixed to a mount portion  578  of the camshaft cover member  179  by bolts  580  via a seal member or gasket  582  to close the opening  574 . The opening  574  preferably has a size through which a tool such as, for example, a wrench can pass through. The intake camshaft  172  preferably forms a hexagonal portion  586  at which the wrench is engageable. 
     With the closure member  576  removed, the user, operator, repairperson or mechanic can insert the wrench through the slot  574 . The wrench is engaged with the hexagonal portion  586  of the camshaft  172  to fix the camshaft  172  (i.e., to prevent the camshaft  172  from rotating). 
     The repairperson, for example, thus can easily disassemble the sprocket  188  from the camshaft  172  or assemble the sprocket  188  thereto for maintenance service or for other purposes. Because the drain oil accumulated within the camshaft chamber  180  does not spill out, the engine  32  is less likely to be stained by the oil and the repairperson does not need to pay special attention to prevent a large oil spill. 
     Because the top end of the camshaft cover member  179  is nested in the sprocket  188  in the arrangement, the illustrated sprocket  188  should be disassembled from the camshaft  172  before the cover member  179  is removed. Similarly, in this situation, the wrench inserted through the slot  574  to prevent the camshaft from rotating. The repairperson thus can work easily without the need for a special test for preventing the timing chain or belt  194  (FIG. 3) from moving or preventing the vanes  260  from rotating. Accordingly, the amount of labor needed can be reduced. 
     In addition, no large change in configuration on the camshaft or on components around the camshaft is necessary and an ordinary tool such as the wrench can be used. Thus, the outboard motor does not need to provide a large space for a special construction and does not require additional labor for the maintenance service. 
     Other polygon shaped portions can replace the hexagonal portion  586  of the camshaft  172 . For example, a triangular shape or a rectangular shape can be applied as the polygon shape. 
     In addition, the access opening  574  can be in the fan of, for example, a slot, a circular, or a rectangular configuration. 
     Control System 
     With reference to FIG. 9, a valve timing control system of the VVT mechanism  40  using the ECU  201  is described below. 
     FIG. 9 schematically illustrates the engine  32 . The illustrated ECU  201  adjusts the valve timing of the intake valves  134  by changing the angular positions of the intake camshaft  172  relative to the sprocket  188  through the VVT mechanism  40 . The ECU  201  also controls the fuel injectors  198  using the fuel injection control unit  202 . The ECU  201  is connected to the OCV  314  as the control section  246  of the VVT mechanism  40  and the fuel injectors through control signal lines. 
     In order to control the VVT mechanism  40  and the fuel injectors  198 , the ECU  201  can employ various sensors which sense operational conditions of the engine  32  and/or the outboard motor  30 . In the present system, the ECU  201  uses a camshaft angle position sensor  350 , a crankshaft angle position sensor  352 , a throttle position sensor (or throttle valve opening degree sensor)  354  and an intake pressure sensor  356 . The ECU  201  is connected to the sensors  350 ,  352 ,  354 ,  356  through sensor signal lines. 
     With reference to FIGS. 2,  4  and  10 , the camshaft angle position sensor  350  preferably is associated with the intake camshaft  172  to sense an angular position of the intake camshaft  172  and sends a camshaft angle position signal to the ECU  201  through the signal line. 
     The camshaft position sensor  350  preferably is positioned adjacent to a portion of the camshaft  172  located between the second and third cylinders of the engine  32 . That is, the sensor  350  is placed below the housing section  316  of the OCV  314  of the VVT mechanism  240 , more specifically, below the opening  574 , and above the fuel pump assembly  500 . The sensor  350  preferably is located above the top end  70  of the bottom cowling member  66 . The position sensor  350  preferably is mounted on a mount portion  600  of the camshaft cover member  179  with a flange portion  602  of the sensor  350  affixed to the mount portion  600  by a bolt  604 . A longitudinal axis  606  of the position sensor  350  preferably extends generally horizontally and generally parallel to the center vertical plane VP. 
     A projection  610  is formed on a surface of the intake camshaft  172  close proximately to a tip portion of the camshaft position sensor  350 . When the camshaft  172  rotates, the projection  610  approaches to and recedes from the tip portion of the sensor  350  for every rotation of the camshaft  172 . The sensor  350  detects the approach or receding of the projection  610  and generates the signal indicative of the camshaft angular position. 
     The positioning of the camshaft angle position sensor  350  is advantageous because the user, operator, mechanic, or repairperson can easily access the sensor  350  for maintenance or for other purposes by merely detaching the upper cowling member  64 . Nothing conceals the sensor  350 . 
     The sensor  350  is not obstructive to the VVT mechanism  240  because the sensor  350  is disposed completely below the VVT mechanism  240 . In other words, the VVT mechanism  240  can be disposed at a most preferred position without being obstructed by the sensor  350 . 
     In addition, because of using a space between the VVT mechanism  240  and the fuel pump assembly  500 , the positioning of the sensor  350  can contribute to make the outboard motor  30  compact. 
     The positioning of the sensor  350  relative to the camshaft  172  is accurate because the sensor  350  is mounted on the camshaft cover member  179  which abuts the cylinder head member  108  at least at the portion  572  without interposing the seal member  570 . 
     Further, vibration of the engine  32  is inhibited from being conducted to the sensor  350  because of the seal member  570 . 
     With reference to FIG. 9, the crankshaft angle position sensor  352  is associated with the crankshaft  118  to sense an angular position of the crankshaft  118  and sends a crankshaft angle position signal to the ECU  201  through the signal line. Any conventional crankshaft angle position sensors and any conventional arrangements thereof can be applied. 
     Both the camshaft angle position sensor  350  and the crankshaft angle position sensor  352  in the present system generate pulses as the respective signals. The pulse of the camshaft position sensor  350  can give an actual angular position of the camshaft  172 . The crankshaft position signal together with the camshaft position signal allows the ECU  201  to accurately determine the position of the camshaft  172  in relation to the crankshaft  118 . 
     With continued reference to FIG. 9, the throttle position sensor  354  preferably is disposed atop the valve shaft  154  to sense an angular position between the open and closed angular positions of the throttle valves  152  and sends a throttle valve position signal to the ECU  201  through the signal line. 
     The intake sensor  356  preferably is disposed either within one of the intake passages  130  or within the plenum chamber  132  to sense an intake pressure therein. Because the respective intake passages  130  are formed such that each generally is the same size as the others, and because the plenum chamber  132  collects a large volume of air that is supplied to each of the intake passages  130 , every passage  130  has substantially equal pressure and a signal of the intake pressure sensor  356  thus can represent a condition of the respective pressure. Thus, it should be appreciated that a single pressure sensor or multiple pressure sensors can be used. 
     The throttle valve position sensor  354  and the intake pressure sensor  356  preferably are selected from a type of sensor that indirectly senses an amount of air in the induction system. Another type of sensor that directly senses the air amount, of course, can be applicable. For example, moving vane types, heated wire types and Karman Vortex types of air flow meters also can be used. 
     The operator&#39;s demand or engine load, as determined by the throttle opening degree, is sensed by the throttle position sensor  354 . Generally, in proportion to the change of the throttle opening degree, the intake air pressure also varies and is sensed by the intake pressure sensor  356 . The throttle valve  152  (FIG. 3) is opened when the operator operates the throttle lever to increase power output of the engine  32  and thus the speed of the watercraft  40 . The intake pressure almost simultaneously decreases as the throttle valve  152  opens. 
     The engine load can also increase when the associated watercraft  40  is moving against wind. In this situation, the operator also operates the throttle lever to recover the speed that may be lost. Therefore, as used in this description, the term “acceleration” means not only the acceleration in the narrow sense but also the recovery of speed by the operator in a broad sense. Also, the term “sudden acceleration” means the sudden acceleration in the narrow sense and a quick recovery of speed by the operator in a broad sense. 
     The signal lines preferably are configured with hard-wires or wire-harnesses. The signals can be sent through emitter and detector pairs, infrated radiation, radio waves or the like. The type of signal and the type of connection can be varied between sensors or the same type can be used with all sensors which are described above and additional sensors described below. 
     Signals from other sensors or control signals also can be used for the control by the ECU  201 . In the present control system, various sensors other than the sensors described above are also provided to sense the operational condition of the engine  32  and/or the outboard motor  30 . For example, an oil pressure sensor  360 , a water temperature sensor  362 , an engine body temperature sensor  364 , a knock sensor  366 , an oxygen sensor  370  for determining a current air/fuel ratio, a transmission position sensor  372 , a transmission position change operation sensor  374 , and an intake air temperature sensor  376  are provided in the present control system. The sensors except for the transmission sensor  372  and the transmission position change operation sensor  374  can sense the operational conditions of the engine  32  and send signals to the ECU  201  through respective sensor signal lines. The transmission position sensor  372  senses whether the transmission  232  (FIG. 1) is placed at the forward, neutral or reverse position and sends a transmission position signal to the ECU  201  through the signal line. The transmission position change operation sensor  374  senses whether the transmission position change operation is conducted and sends a transmission position change operation signal to the ECU  201  through the signal line. An ignition control signal  378 , a fuel injection control signal  380 , and an AAD control signal  382  are also used by the ECU  201  for control of the spark plugs  203  (FIG.  2 ), the fuel injectors  198 , and the AAD (not shown), respectively. The foregoing sensors  350 - 376  and the control signals  378 - 382 , in a broad sense, define sensors  380  that sense operational conditions of the engine and/or the outboard motor. 
     The ECU  201  can be designed as a feedback control device using the signals of the sensors. The ECU  201  preferably has a central processing unit (CPU) and some storage units which store various control maps defining relationships between parameters such as, for example, the engine speed, the throttle valve position and the intake pressure (and/or an amount of intake air) to determine an optimum control conditions. The ECU  201  then controls the VVT mechanism  40 , the fuel injectors  198  and other actuators in accordance with the determined control condition. 
     The fuel injection control unit  202  can be in the form of a hard-wired circuit, a dedicated processor and memory, or a general purpose processor and memory running one or a plurality of control programs. Other units, described below, can also be constructed as a hard-wired circuit, a dedicated processor and memory, or a general purpose processor and memory running one or a plurality of control programs. However, for easier understanding of the reader, the units will be described as if they were discriminate and substantial units. The illustrated fuel injection control unit  202  controls the fuel injectors  198  using at least the throttle position signal from the throttle position sensor  354  and the intake pressure signal from the intake pressure sensor  356 . 
     The ECU  201  preferably comprises, other than the fuel injection control unit  202 , an actual camshaft angular position calculation (ACAPC) unit  384 , an engine speed calculation unit  386 , a target camshaft angular position calculation (TCAPC) unit  388 , and a control value calculation unit  390 . The TCAPC unit  388  and the control value calculation unit  390  together form an OCV control section  392  in the illustrated ECU configuration. 
     The ACAPC unit  384  preferably receives the actual camshaft angular position signal from the camshaft angle position sensor  350  and the crankshaft angular position signal, which gives two possible ranges of camshaft angular position, from the crankshaft angle position sensor  352 . The ACAPC unit  384  then calculates a deviation value which indicates how much the actual camshaft angular position deviates within the two possible ranges of camshaft angular position. 
     The engine speed calculation unit  386  receives the crankshaft angular position signal from the crankshaft angle position sensor  352  and calculates an engine speed using the signal versus time. 
     The TCAPC unit  388  receives the deviation value from the ACAPC unit  384 , the engine speed from the engine speed calculation unit  386  and at least one of the throttle valve opening degree signal from the throttle valve position sensor  354  and the intake pressure signal from the intake pressure sensor  356 . The TCAPC unit  388  then calculates a target camshaft angular position based upon the deviation value, the engine speed and either the throttle valve opening degree signal or the intake pressure signal. 
     The control value calculation unit  390  receives the target camshaft angular position from the TCAPC unit  388  and calculates a control value of the OCV  314  of the VVT mechanism  40 . That is, the control value calculation unit  390  determines how much fluid should be delivered to either the space S 1  or the space S 2  of the adjusting section  242  of the VVT mechanism  40  based upon the target camshaft angular position. 
     Under a normal running condition and an ordinary acceleration condition (i.e., not sudden acceleration condition), the ECU  201  preferably uses either a combination of the throttle valve opening degree signal with the engine speed signal (α-N method) or a combination of the intake pressure signal with the engine speed signal (D-j method) to calculate the target camshaft angular position. Otherwise, the ECU  201  can use a mixed combination of the α-N method and the D-j method under the normal running condition or the ordinary acceleration condition. The α-N method, the D-j method and the mixed combination thereof are disclosed in, for example, a co-pending U.S. application filed Feb. 14, 2002, titled CONTROL SYSTEM FOR MARINE ENGINE, which Ser. No. is 10/078,275, the entire contents of which is hereby expressly incorporated by reference. An air amount signal sensed by the air flow meter noted above can be applied additionally or instead either the intake pressure signal or the throttle opening degree signal. 
     Under a sudden acceleration condition, the illustrated ECU  201  uses only the throttle opening degree signal. That is, the ECU  201  always determines, at least prior to controlling the OCV  314  with the OCV control section  392 , whether the operator wishes sudden acceleration or not. The sudden acceleration condition preferably is determined when a change rate of the throttle opening degree signal, a change rate of the intake pressure signal or a change rate of the engine speed calculated by the engine speed calculation unit  386  becomes greater than a predetermined magnitude. A change rate of the air amount signal also can be used to determine the sudden acceleration condition. Theoretically, the predetermined magnitude can be set at any magnitude larger than zero. 
     Of course, the foregoing description is that of preferred controls having certain features, aspects and advantages in accordance with the present invention. Various changes and modifications also may be made to the above-described controls without departing from the spirit and scope of the invention, as defined by the claims.