Abstract:
A watercraft has an engine that is controlled to reduce the likelihood of engine stall when the watercraft engine speed is rapidly decreased while the watercraft is in a planing mode. The engine is controlled by a method that detects a rapid engine speed decrease when the watercraft is believed to be in the planing mode. A operational characteristic of the engine is adjusted to increase the engine speed such that, after the engine reaches a stable engine speed, the stable engine speed is higher than a desired idle speed. The operational characteristic can be an advance in ignition timing or an increase in airflow to the engine.

Description:
PRIORITY INFORMATION  
         [0001]    This application is based on and claims priority to Japanese Patent Application No. 2000-230968, filed Jul. 31, 2000, the entire contents of which is hereby expressly incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present application generally relates to an engine control arrangement for controlling a four-stroke watercraft, and more particularly relates to an engine management system that prevents engine stalling under rapid deceleration.  
           [0004]    2. Description of the Related Art  
           [0005]    Watercraft, including personal watercraft and jet boats, are often powered by an internal combustion engine having an output shaft arranged to drive a water propulsion device. Occasionally, rapid deceleration occurs at high watercraft speeds and, because watercraft do not have brakes, water resistance experienced along the sides of the hull are the primary source of deceleration.  
           [0006]    Watercraft often operate within three modes of operation: displacement mode, transition mode and planing mode. During lower speeds, the hull displaces water to remain buoyant; this is the displacement mode. At a particular watercraft speed relative to the water, a portion of the hull rises up from the water and the watercraft begins planing across the water; this is the planing mode. Of course, the transition mode occurs between the displacement mode and the planing mode and involves the range of watercraft speeds that cause a transition between the planing and displacement modes.  
           [0007]    Importantly, while the watercraft is planing (i.e., up on plane), the wetted surface area of the watercraft is decreased and the water resistance is substantially reduced. On the other hand, once the watercraft slows to a speed that brings the watercraft off plane (i.e., transition mode and/or displacement mode), the wetted surface area of the watercraft is significantly increased and the water resistance dramatically increases. Because the water resistance is higher in non-planing modes, the rate of deceleration of the watercraft is also higher in the non-planing modes than in the planing mode.  
           [0008]    To move from the planing mode to either the transition mode or the displacement mode, a throttle valve often is rapidly closed to cause the watercraft to decelerate. In some instances, the throttle valve is allowed to close almost entirely under the biasing force of a return spring that acts against a throttle valve control cable and operation (i.e., finger or thumb paddle). This rapid closure of the throttle valve can induce a rapid deceleration state.  
           [0009]    In a rapid deceleration state, the air supplied to the cylinder bores of the engine decreases at a much faster rate than the control system controlling a set of fuel injectors can react. Thus, the amount of fuel being injected into the cylinders is excessive with respect to the amount of air entering the cylinders; a rich air-fuel mixture results. An overly rich mixture tends to cause an engine to stall. In addition, because the speed of the water passing the propulsion device tends to affect engine speed, the move from planing mode can cause the engine speed to decrease even more rapidly once the watercraft moves out of the planing mode and into the displacement mode. Thus, the engine is susceptible to stalling during rapid deceleration.  
           [0010]    An additional problem in watercraft is irregularity in engine idle speed caused by variances in the air/fuel ratio. The variances generally are caused by condensation of the fuel within the combustion chamber and/or the induction system. In particular, when the engine is operated below a certain temperature, the fuel in the air/fuel mixture tends to condense on the walls of the intake manifold, the intake port and the cylinder walls. Such condensation increases the air/fuel ratio, which adversely affects engine performance.  
         SUMMARY OF THE INVENTION  
         [0011]    Accordingly, an engine control arrangement has been developed to better control engine speed during rapid deceleration in order to prevent stalling. In addition, the engine control arrangement can be configured to maintain the air/fuel mixture at a desired ratio by adding more fuel at lower temperatures to return the air/fuel ratio to a desired level.  
           [0012]    Thus, one aspect of the present invention involves a method of controlling a marine engine associated with a watercraft. The method comprises sensing a rapid deceleration when the watercraft is in a planing mode, altering an engine operating parameter to increase the engine speed when the rapid deceleration occurs when the watercraft is in the planing mode, sensing when an engine speed has attained a stabilized engine speed lower than an engine speed associated with the planing mode and returning the engine operating parameter to normal after then engine speed has attained the stabilized engine speed.  
           [0013]    Another aspect of the present invention involves a personal watercraft comprising a hull adapted for at least two modes of operation: a planing mode and a displacement mode. An engine is disposed within the hull. The engine comprises a cylinder defined by a cylinder wall. A piston is reciprocally mounted within the cylinder. A combustion chamber is at least partially defined by the piston. The piston is drivingly connected to a crankshaft. A crankshaft sensor is adapted to sense a speed of the crankshaft. An induction system supplies air to the combustion chamber. A throttle valve is disposed within the induction system. An induction sensor is adapted to sense an airflow into the combustion chamber. An ignition system comprises an igniter that is disposed within the combustion chamber to ignite an air-fuel charge within the combustion chamber. A controller is in electrical communication with the crankshaft sensor and the induction system. The controller is adapted to adjust an engine operating parameter if the watercraft is in the planing mode and if the engine undergoes a rapid decrease in engine speed. The engine operating parameter is adjusted such that a rate of engine speed decrease is slowed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    These and other aspects of the present invention are described in detail below with reference to the accompanying drawings. The drawings comprise 13 figures.  
         [0015]    [0015]FIG. 1 is a side elevational view of a personal watercraft of the type powered by an engine controlled in accordance with certain features, aspects and advantages of the present invention. Several of the internal components of the watercraft (e.g., the engine) are illustrated in phantom.  
         [0016]    [0016]FIG. 2 is a top plan view of the watercraft of FIG. 1.  
         [0017]    [0017]FIG. 3 is a perspective view of the engine viewed from a slightly forward location on the starboard side.  
         [0018]    [0018]FIG. 4 is a perspective view of the engine viewed from a slightly forward location on the port side.  
         [0019]    [0019]FIG. 5 is a schematic, cross-sectional rear view of the watercraft and the engine. A profile of a hull of the watercraft is shown schematically. Portions of the engine and an opening of an engine compartment of the hull are illustrated partially in section.  
         [0020]    [0020]FIG. 6 is a schematic view showing the engine control system, including at least a portion of the engine in cross-section, an ECU, and a simplified fuel injection system.  
         [0021]    [0021]FIG. 7 is a block diagram showing a control routine arranged and configured in accordance with certain features, aspects and advantages of the present invention.  
         [0022]    [0022]FIG. 8 is a block diagram showing another control routine arranged and configured in accordance with certain features, aspects and advantages of the present invention.  
         [0023]    [0023]FIG. 9 a  is a diagram illustrating a throttle valve position over time.  
         [0024]    [0024]FIG. 9 b  is a diagram illustrating the amount of fuel being injected into the engine as a percentage when the throttle valve is moved in the manner shown in FIG. 9 a.    
         [0025]    [0025]FIG. 9 c  is a diagram illustrating ignition timing or ISC device position over time.  
         [0026]    [0026]FIG. 9 d  is a diagram illustrating the speed of the engine in revolutions per minute (RPM) when the engine is operated in the manner shown in FIGS. 9 a  through  9   c.    
         [0027]    [0027]FIG. 10 is a block diagram showing another control routine arranged and configured in accordance with certain features, aspects and advantages of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]    With reference to FIGS.  1  to  6 , an overall configuration of a personal watercraft  10  and its engine  12  will be described. The watercraft  10  employs the internal combustion engine  12 , which preferably is configured in accordance with a preferred embodiment of the present invention. The described engine configuration and the associated control routine have particular utility for use within the personal watercraft, and thus, are described in the context of personal watercraft. The engine configuration and the control routine, however, also can be applied to other types of watercraft, such as, for example, small jet boats and other vehicles that feature marine drives.  
         [0029]    With reference initially to FIG. 1, the personal watercraft  10  includes a hull  14  formed with a lower hull section  16  and an upper hull section or deck  18 . The lower hull section  16  and the upper hull section  18  preferably are coupled together to define an internal cavity  20  (see FIG. 5). A bond flange  22  defines an intersection of both of the hull sections  16 ,  18 .  
         [0030]    With reference to FIGS. 2 and 5, an imaginary center plane CP extends generally vertically from bow to stem through the watercraft  10 . Along the center plane CP, the illustrated upper hull section  14  preferably comprises a hatch cover  24 , a control mast  26  and a seat  28 , which are arranged generally in seriatim from fore to aft.  
         [0031]    In the illustrated arrangement, a forward portion of the upper hull section  18  defines a bow portion  30  that slopes upwardly. An opening can be provided through the bow portion  30  so the rider can access the internal cavity  20 . The hatch cover  24  can be detachably affixed (e.g., hinged) to the bow portion  30  to resealably cover the opening.  
         [0032]    The control mast  26  extends upwardly to support a handle bar  32 . The handle bar  32  is provided primarily for controlling the direction of the watercraft  10 . The handle bar  32  preferably carries other mechanisms, such as, for example, a throttle lever  34  that is used to control the engine output (i.e., to vary the engine speed).  
         [0033]    The seat  28  extends rearwardly along the center plane CP from a portion just rearward of the bow portion  30 . In some configurations, the seat  28  is disposed atop a pedestal  29  (see FIG. 1). In the illustrated arrangement, the seat  28  has a saddle shape. Hence, a rider can sit on the seat  28  in a straddle fashion and the illustrated seat  28  often is referred to as a straddle-type seat.  
         [0034]    Foot areas  34  are defined on both sides of the seat  28  along a portion of the top surface of the upper hull section  18 . The foot areas  34  are formed generally flat but may be inclined toward a suitable drain configuration.  
         [0035]    The seat  28  can be formed atop a cover member (not shown) that closes an access opening  36  formed within the pedestal  29 . The access opening  36  generally provides suitable access to the internal cavity  20  and, in the illustrated arrangement, to the engine  12 . In the illustrated embodiment, the upper hull section  18  or pedestal  29  also encloses a storage box  38  that is disposed under the seat  28 .  
         [0036]    A fuel tank  40  is positioned in the cavity  20  under the bow portion  30  of the upper hull section  18  in the illustrated arrangement. A duct (not shown) preferably couples the fuel tank  40  with a fuel inlet port positioned at a top surface of the bow  30  of the upper hull section  18 . A closure cap  42  (see FIG. 2) closes the fuel inlet port to inhibit water infiltration.  
         [0037]    The engine  12  is disposed in an engine compartment defined, for instance within the cavity  20 . The engine compartment preferably is located under the seat  28 , but other locations are also possible (e.g., beneath the control mast or in the bow). The rider thus can access the engine  12  in the illustrated arrangement through the access opening  36  by detaching the seat  28 . In general, the engine compartment is defined within the cavity  20  by a forward and rearward bulkhead. Other configurations, however, are possible.  
         [0038]    A pair of air ducts  44  are provided in the illustrated arrangement such that the air within the internal cavity  20  can be readily replenished or exchanged. The engine compartment, however, is substantially sealed to protect the engine  12  and other internal components from water.  
         [0039]    A jet pump unit  46  propels the illustrated watercraft  10 . Other types of marine drives can be used depending upon the application. The jet pump unit  46  preferably is disposed within a tunnel  48  formed on the underside of the lower hull section  16 . The tunnel  48  has a downward facing inlet port  50  opening toward the body of water. A jet pump housing  52  is disposed within a portion of the tunnel  48 . Preferably, an impeller (not shown) is supported within the housing  52 .  
         [0040]    An impeller shaft  54  extends forwardly from the impeller and is coupled with a crankshaft  56  of the engine  12  by a suitable coupling member  58 . The crankshaft  56  of the engine  12  thus drives the impeller shaft  54 . The rear end of the housing  52  defines a discharge nozzle  57 . A steering nozzle  60  is affixed proximate the discharge nozzle  57 . The nozzle can be pivotally moved about a generally vertical steering axis. The steering nozzle  60  is connected to the handle bar  32  by a cable or other suitable arrangement so that the rider can pivot the nozzle  60  for steering the watercraft.  
         [0041]    The engine  12  in the illustrated arrangement operates on a four-stroke cycle combustion principal. With reference to FIG. 5, the engine  12  includes a cylinder block  62  with four cylinder bores  65  formed side by side along a single plane CA. This plane CA, however, preferably is inclined relative to the generally vertical center plane CP to lower the vertical profile of the engine. The engine  12 , thus, is an inclined L 4  (in-line four cylinder) type. The illustrated engine, however, merely exemplifies one type of engine on which various aspects and features of the present invention can be used. Engines having a different number of cylinders, other cylinder arrangements, other cylinder orientations (e.g., upright cylinder banks, V-type, and W-type), and operating on other combustion principles (e.g., crankcase compression two-stroke, diesel, and rotary) are all practicable.  
         [0042]    With continued reference to FIG. 5, a piston  64  reciprocates in each of the cylinder bores  65  formed within the cylinder block  62 . A cylinder head member  66  is affixed to the upper end of the cylinder block  62  to close respective upper ends of the cylinder bores  65 . The cylinder head member  66 , the cylinder bores  65  and the pistons  64  together define combustion chambers  68 .  
         [0043]    A lower cylinder block member or crankcase member  70  is affixed to the lower end of the cylinder block  62  to close the respective lower ends of the cylinder bores  65  and to define, in part, a crankshaft chamber. The crankshaft  56  is journaled between the cylinder block  62  and the lower cylinder block member  70 . The crankshaft  56  is rotatably connected to the pistons  64  through connecting rods  74 . Preferably, a crankshaft speed sensor  105  is disposed proximate the crankshaft to output a signal indicative of engine speed. In some configurations, the crankshaft speed sensor  105  is formed, at least in part, with a flywheel magneto. The speed sensor  105  also can output crankshaft position signals in some arrangements.  
         [0044]    The cylinder block  62 , the cylinder head member  66  and the crankcase member  70  together generally define the engine  12 . The engine  12  preferably is made of an aluminum based alloy. In the illustrated embodiment, the engine  12  is oriented in the engine compartment to position the crankshaft  56  generally parallel to the central plane CP. Other orientations of the engine, of course, are also possible (e.g., with a transversely or vertically oriented crankshaft).  
         [0045]    Engine mounts  76  preferably extend from both sides of the engine  12 . The engine mounts  76  can include resilient portions made of, for example, a rubber material. The engine  12  preferably is mounted on the lower hull section  16 , specifically, a hull liner, by the engine mounts  76  so that the engine  12  is greatly inhibited from conducting vibration energy to the hull section  16 .  
         [0046]    The engine  12  preferably includes an air induction system to introduce air to the combustion chambers  68 . In the illustrated embodiment, the air induction system includes four air intake ports  78  defined within the cylinder head member  66 , which ports  78  generally correspond to and communicate with the four combustion chambers  68 . Other numbers of ports can be used depending upon the application. Intake valves  80  are provided to open and close the intake ports  78  such that flow through the ports  78  can be controlled. A camshaft arrangement that can be used to control the intake valves  80  is discussed below.  
         [0047]    The air induction system also includes an air intake box  82  for smoothing intake airflow and acting as an intake silencer. The intake box  82  in the illustrated embodiment is generally rectangular and, along with an intake box cover  87 , defines a plenum chamber  84 . The intake box cover  87  can be attached to the intake box  82  with a number of intake box cover clips  81  or any other suitable fastener. Other shapes of the intake box of course are possible, but the plenum chamber preferably is as large as possible while still allowing for positioning within the space provided in the engine compartment.  
         [0048]    With reference now to FIG. 5, in the illustrated arrangement, air is introduced into the plenum chamber  84  through a pair of air inlet ports  85  and a filter  83 . With reference to FIG. 6, the illustrated air induction system preferably also includes a bypass passage or an idle speed control device (ISC)  94  that can be controlled by an Electronic Control Unit (ECU)  92 . In one advantageous arrangement, the ECU  92  is a microcomputer that includes a microcontroller having a CPU, a timer, RAM, and ROM. Of course, other suitable configurations of the ECU also can be used. Preferably, the ECU  92  is configured with or capable of accessing various maps to control engine operation in a suitable manner.  
         [0049]    In general, the ISC device comprises an air passage the bypasses the throttle valve  90 . Air flow through the air passage of the ISC device preferably is controlled with a suitable valve, such as a needle valve or the like. In this manner, the air flow amount can be controlled in accordance with a suitable control routine, one of which will be discussed below.  
         [0050]    With continued reference to FIG. 5, in the illustrated arrangement, the throttle bodies  86  slant toward the port side relative to the center axis CA of the engine  12 . Respective top ends  89  of the throttle bodies  86 , in turn, open upwardly within the plenum chamber  84 . Air in the plenum chamber  84  thus is drawn through the throttle bodies  86  and the intake ports  78  into the combustion chambers  68  when negative pressure is generated in the combustion chambers  68 . The negative pressure is generated when the pistons  64  move toward the bottom dead center position from the top dead center position during the intake stroke.  
         [0051]    With reference again to FIG. 6, a throttle valve position sensor  88  preferably is arranged proximate a throttle valve shaft assembly  90  in the illustrated arrangement. The sensor  88  preferably generates a signal that is representative of either absolute throttle position or movement of the throttle shaft. In any event, the signal from the throttle valve position sensor  88  preferably corresponds generally to the engine load, as may be indicated by the degree of throttle opening. In some applications, a manifold pressure sensor  93  can be provided to detect engine load. The signal from the throttle position sensor  88  (and/or manifold pressure sensor  93 ) can be sent to the ECU  92  via a throttle position data line. The signal can be used to control various aspects of engine operation, such as, for example, but without limitation, fuel injection amount, fuel injection timing, ignition timing, ISC valve positioning and the like.  
         [0052]    The engine  12  also includes a fuel injection system which preferably includes four fuel injectors  96 , each having an injection nozzle exposed to the intake ports  78  so that injected fuel is directed toward the combustion chambers  68 . Thus, in the illustrated arrangement, the engine  12  features port fuel injection. It is anticipated that various features, aspects and advantages of the present invention also can be used with direct or other types of indirect fuel injection systems.  
         [0053]    With reference again to FIG. 6, fuel is drawn from the fuel tank  40  by a fuel pump  100 , which is controlled by the ECU  92 . The fuel is delivered to the fuel injectors  96  through a fuel delivery conduit  102 . A fuel return conduit  104  also is provided between the fuel injectors and the fuel tank  40 . Excess fuel that is not injected by the fuel injector  96  returns to the fuel tank  40  through the conduit  104 . The flow generated by the return of the unused fuel from the fuel injectors aids in cooling the fuel injectors.  
         [0054]    In operation, a predetermined amount of fuel is sprayed into the intake ports  78  via the injection nozzles of the fuel injectors  96 . The timing and duration of the fuel injection is dictated by the ECU  92  based upon any desired control strategy. In one presently preferred configuration, the amount of fuel injected is determined based, at least in part, upon the sensed throttle valve position. The fuel charge delivered by the fuel injectors  96  then enters the combustion chambers  68  with an air charge when the intake valves  80  open the intake ports  78 .  
         [0055]    The engine  12  further includes an ignition system. In the illustrated arrangement, four spark plugs  106  are fixed on the cylinder head member  66 . The electrodes of the spark plugs  106  are exposed within the respective combustion chambers  68 . The spark plugs  106  ignite an air/fuel charge just prior to, or during, each power stroke, preferably under the control of the ECU  92  to ignite the air/fuel charge therein.  
         [0056]    The engine  12  further includes an exhaust system  108  to discharge burnt charges, i.e., exhaust gases, from the combustion chambers  68 . In the illustrated arrangement, the exhaust system  108  includes four exhaust ports  110  that generally correspond to, and communicate with, the combustion chambers  68 . The exhaust ports  110  preferably are defined in the cylinder head member  66 . Exhaust valves  112  preferably are provided to selectively open and close the exhaust ports  110 . A suitable exhaust cam arrangement, such as that described below, can be provided to operate the exhaust valves  112 .  
         [0057]    A combustion condition or oxygen sensor  107  preferably is provided to detect the in-cylinder combustion conditions by sensing the residual amount of oxygen in the combustion products at a point in time very close to when the exhaust port is opened. The signal from the oxygen sensor  107  preferably is delivered to the ECU  92 . The oxygen sensor  107  can be disposed within the exhaust system at any suitable location. In the illustrated arrangement, the oxygen sensor  107  is disposed proximate the exhaust port  110  of a single cylinder. Of course, in some arrangements, the oxygen sensor can be positioned in a location further downstream; however, it is believed that more accurate readings result from positioning the oxygen sensor upstream of a merge location that combines the flow of several cylinders.  
         [0058]    With reference now to FIG. 3, the illustrated exhaust system  108  preferably includes two small exhaust manifolds  114 ,  115  that each receive exhaust gases from a pair of exhaust ports  110  (i.e., a pair of cylinders). The respective downstream ends of the exhaust manifolds  114 ,  115  are coupled with a first unitary exhaust conduit  116 . The first unitary conduit  116  is further coupled with a second unitary exhaust conduit  118 . The second unitary conduit  118  is coupled with an exhaust pipe  120  at a location generally forward of the engine  12 .  
         [0059]    The exhaust pipe  120  extends rearwardly along a port side surface of the engine  12 . The exhaust pipe  120  is connected to a water-lock  122  proximate a forward surface of the water-lock  122 . With reference to FIG. 2, a discharge pipe  124  extends from a top surface of the water-lock  122 . The discharge pipe  124  bends transversely across the center plane CP and rearwardly toward a stem of the watercraft. Preferably, the discharge pipe  124  opens at a stem of the lower hull section  16  in a submerged position. As is known, the water-lock  122  generally inhibits water in the discharge pipe  124  or the water-lock itself from entering the exhaust pipe  120 .  
         [0060]    The engine  12  further includes a cooling system configured to circulate coolant into thermal communication with at least one component within the watercraft  10 . Preferably, the cooling system is an open-loop type of cooling system that circulates water drawn from the body of water in which the watercraft  10  is operating through thermal communication with heat generating components of the watercraft  10  and the engine  12 . It is expect that other types of cooling systems can be used in some applications. For instance, in some applications, a closed-loop type liquid cooling system can be used to cool lubricant and other components.  
         [0061]    The present cooling system preferably includes a water pump arranged to introduce water from the body of water surrounding the watercraft  10 . The jet propulsion unit preferably is used as the water pump with a portion of the water pressurized by the impeller being drawn off for use in the cooling system, as is generally known in the art. Preferably, water jackets  111  can be provided around portions of the cylinder block  62  and the cylinder head member  66  (see FIG. 6).  
         [0062]    In some applications, the exhaust system  108  is comprised of a number of double-walled components such that coolant can flow between the two walls (i.e., the inner and outer wall) while the exhaust gases flow within a lumen defined by the inner wall. Such constructions are well known.  
         [0063]    An engine coolant temperature sensor  109  preferably is positioned to sense the temperature of the coolant circulating through the engine. Of course, the sensor  109  could be used to detect the temperature in other regions of the cooling system; however, by sensing the temperature proximate the cylinders of the engine, the temperature of the combustion chamber and the closely positioned portions of the induction system is more accurately reflected.  
         [0064]    With reference again to FIG. 3, the engine  12  preferably includes a secondary air supply system that supplies air from the air induction system to the exhaust system  108 . More specifically, for example, hydrocarbon (HC) and carbon monoxide (CO) components of the exhaust gases can be removed by an oxidation reaction with oxygen (O 2 ) that is supplied to the exhaust system  108  from the air induction system. In one arrangement of the secondary air supply system, a secondary air supply device  122  is disposed next to the cylinder head member  66  on the starboard side. The air supply device  122  defines a generally closed cavity and contains a control valve in the illustrated arrangement. Air supplied from the air supply device  122  passes directly to the exhaust system  108  when the engine  12  is operating in a relatively high speed range and/or under a relatively high load condition because greater amounts of hydrocarbon (HC) and carbon monoxide (CO) are more likely to be present in the exhaust gases under such a condition.  
         [0065]    With reference to FIGS. 5 and 6, the engine  12  preferably has a valve cam mechanism for actuating the intake and exhaust valves  80 ,  112 . In the illustrated embodiment, a double overhead camshaft drive is employed. That is, an intake camshaft  124  actuates the intake valves  80  and an exhaust camshaft  126  separately actuates the exhaust valves  112 . The intake camshaft  124  extends generally horizontally over the intake valves  80  from fore to aft generally in parallel to the center plane CP, and the exhaust camshaft  126  extends generally horizontally over the exhaust valves  112  from fore to aft also generally in parallel to the center plane CP.  
         [0066]    Both the intake and exhaust camshafts  124 ,  126  are journaled in the cylinder head member  66  in any suitable manner. A cylinder head cover member  128  extends over the camshafts  124 ,  126 , and is affixed to the cylinder head member  66  to define a camshaft chamber. The secondary air supply device  122  is preferably affixed to the cylinder head cover member  128 . Additionally, the air supply device  122  is desirably disposed between the intake air box and the engine  12 .  
         [0067]    The intake camshaft  124  has cam lobes each associated with the respective intake valves  80 , and the exhaust camshaft  126  also has cam lobes associated with respective exhaust valves  112 . The intake and exhaust valves  80 ,  112  normally close the intake and exhaust ports  78 ,  110  by a biasing force of springs. When the intake and exhaust camshafts  124 ,  126  rotate, the cam lobes push the respective valves  80 ,  112  to open the respective ports  78 ,  110  by overcoming the biasing force of the spring. Air enters the combustion chambers  68  when the intake valves  80  open. In the same manner, the exhaust gases exit from the combustion chambers  68  when the exhaust valves  112  open.  
         [0068]    The crankshaft  56  preferably drives the intake and exhaust camshafts  124 ,  126 . The respective camshafts  124 ,  126  have driven sprockets affixed to ends thereof while the crankshaft  56  has a drive sprocket. Each driven sprocket has a diameter that is twice as large as a diameter of the drive sprocket. A timing chain or belt is wound around the drive and driven sprockets. When the crankshaft  56  rotates, the drive sprocket drives the driven sprockets via the timing chain, and thus the intake and exhaust camshafts  124 ,  126  also rotate.  
         [0069]    The engine  12  preferably includes a lubrication system that delivers lubricant oil to engine portions for inhibiting frictional wear of such portions. In the illustrated embodiment, a dry-sump lubrication system is employed. This system is a closed-loop type and includes an oil reservoir  130 , as illustrated in FIGS. 3 and 4.  
         [0070]    An oil delivery pump is provided within a circulation loop to deliver the oil in the reservoir  130  through an oil filter  132  to the engine portions that are to be lubricated, for example, but without limitation, the pistons  64  and the crankshaft bearings (not shown). The crankshaft  56  or one of the camshafts  124 , 126  preferably drives the delivery pump. The crankshaft  56  or one of the camshafts  124 ,  126  preferably drives the return pump also.  
         [0071]    In order to determine appropriate engine operation control scenarios, the ECU  92  preferably uses these control maps and/or indices stored within the ECU  92  in combination with data collected from various input sensors. The ECU&#39;s various input sensors can include, but are not limited to, the throttle position sensor  90 , the manifold pressure sensor  93 , the engine coolant temperature sensor  109 , the oxygen (O 2 ) sensor  107 , and a crankshaft speed sensor  105 . It should be noted that the above-identified sensors merely correspond to some of the sensors that can be used for engine control and it is, of course, practicable to provide other sensors, such as an intake air pressure sensor, an intake air temperature sensor, a knock sensor, a neutral sensor, a watercraft pitch sensor, a shift position sensor and an atmospheric temperature sensor. The selected sensors can be provided for sensing engine running conditions, ambient conditions or other conditions of the engine  12  or associated watercraft  10 .  
         [0072]    During engine operation, ambient air enters the internal cavity  20  defined in the hull  14  through the air ducts  44 . The air is then introduced into the plenum chamber  84  defined by the intake box  82  through the air inlet ports  85  and drawn into the throttle bodies  86 . The air filter element  83 , which preferably comprises a water-repellent element and an oil resistant element, filters the air. The majority of the air in the plenum chamber  84  is supplied to the combustion chambers  68 . The throttle valves  90  in the throttle bodies  148  regulate an amount of the air permitted to pass to the combustion chambers  68 . The opening angles of the throttle valves  90 , and thus, the airflow across the throttle valves  90 , can be controlled by the rider with the throttle lever  34 . The air flows into the combustion chambers  68  when the intake valves  80  open. At the same time, the fuel injectors  96  spray fuel into the intake ports  78  under the control of ECU. Air/fuel charges are thus formed and delivered to the combustion chambers  68 .  
         [0073]    The air/fuel charges are fired by the spark plugs  106  under the control of the ECU. The burnt charges, i.e., exhaust gases, are discharged to the body of water surrounding the watercraft  10  through the exhaust system  108 . A relatively small amount of the air in the plenum chamber  84  is supplied to the exhaust system  108  so as to aid in further combustion of any unburned fuel remaining in the exhaust gases.  
         [0074]    The combustion of the air/fuel charges causes the pistons  64  to reciprocate and thus causes the crankshaft  56  to rotate. The crankshaft  56  drives the impeller shaft  54  and the impeller rotates in the hull tunnel  48 . Water is thus drawn into the tunnel  48  through the inlet port  50  and then is discharged rearward through the steering nozzle  60 . The rider steers the nozzle  60  by the steering handle bar  32 . The watercraft  10  thus moves as the rider desires.  
         [0075]    With reference now to FIG. 7, a control arrangement is shown that is arranged and configured in accordance with certain features, aspects and advantages of the present invention. The control routine begins and moves to a first decision block P 1  in which the engine speed is compared to a predetermined engine planing speed “A” (e.g., A can be about 6000 RPM in some applications). Preferably, the predetermined engine planing speed is an engine speed that generally corresponds to a watercraft speed that places the watercraft in the planing mode.  
         [0076]    If the speed is greater than “A”, the routine proceeds to a decision block P 2  in which the throttle position is checked to determine if the throttle position reflects a position or rate of change associated with rapid throttle closure. In the illustrated arrangement, a generally closed throttle position while the watercraft engine is operating at a high engine speed would indicate that the throttle valve has been rapidly closed. Hence, in the illustrated arrangement of FIG. 7, the sensed throttle angle is compared to a predetermined throttle angle “B”, which can be about 5 degrees in some arrangements.  
         [0077]    If the sensed throttle angle is less than “B”, then the routine proceeds to an operation block P 3  where the ignition timing is advanced to a predetermined value. After the ignition timing is advanced, the routine repeats. Preferably, the routine repeats substantially continuously during engine operation.  
         [0078]    Returning to the decision block P 1  and the decision block P 2 , if the engine speed is determined to be less than “A” or if the throttle position is greater than “B”, then the routine proceeds to a decision block P 4  where the stabilization of engine operation is checked. In one configuration, the routine checks whether a preset period of time, which can be determined empirically, has passed. After the predetermined period of time has passed, then the engine operation would be sufficiently stabilized to stop advancing the ignition timing because the fuel injector control system would adequately reflect the engine speed and the air fuel mixture would not be overly rich to the point of causing engine stall. Of course, in some applications, such as that reflected in FIG. 9, the period of time can be a period of time in which the engine speed has substantially stabilized (i.e., an absence of wide changes in engine speed) at a speed lower than the speed associated with the planing mode of the watercraft. Thus, after the engine has operated for a predetermined period of time at a substantially constant speed that is lower than the speed associated with beginning the planing mode, then the routine continues to an operation block P 5 . In the operation block P 5 , the ignition timing is retarded to normal operation (i.e., the temporary advance in ignition timing is removed). The routine then repeats.  
         [0079]    As illustrated, if, in the decision block P 4 , the engine has not had enough time to stabilize, then the routine repeats without adjusting the ignition timing.  
         [0080]    With reference now to FIG. 8, another control routine that is arranged and configured in accordance with certain features, aspects and advantages of the present invention is illustrated. After starting, this routine proceeds to decision block P 10  where the sensed engine speed is compared to a predetermined engine speed “A” (e.g., “A” can be 6000 RPM in some applications). If the sensed engine speed is greater than “A”, the routine proceeds to a decision block P 12 , where the sensed throttle position is compared to a predetermined angle “B”, which may be about 5 degrees in some applications. As discussed above, the predetermined angle in combination with the predetermined engine speed are used to determine whether a rapid throttle valve closure has occurred. In some applications, the rate of throttle valve movement can be monitored. In such applications, engine speed or watercraft speed can be used to determine whether the rapid closure of the throttle valve may pose concerns over engine stall (e.g., the watercraft or engine speed reflects a planing mode).  
         [0081]    In the decision block P 12 , if the throttle angle is less than “B”, then the routine continues to the operation block P 13  where the airflow regulating valve of the ISC device is opened to increase the flow of air to the combustion chamber. The routine then repeats as long as the engine is operating.  
         [0082]    Returning again to the decision block P 10  and the decision block P 12 , if either the sensed engine speed is less than “A” or the sensed throttle position is less than “B”, then the routine proceeds to a decision block P 14  in which stabilization of engine speed is checked in the manner set forth above in the discussion of the control routine shown in FIG. 7. If the engine speed has stabilized, then the routine continues to an operation block P 15  where the valve of the idle speed control device is closed. If, however, the engine speed has not stabilized, then the routine repeats again.  
         [0083]    With reference now to FIG. 9, the effect on engine operation of both the routine illustrated in FIG. 7 and the routine illustrated in FIG. 8 are graphically depicted. As illustrated, the throttle position change illustrated in FIG. 9 a  shows an example of a rapidly closed throttle valve (i.e., the time “a” in which the throttle valve closes is very short). As a result of the closure of the throttle valve, the engine begins to rapidly decrease from a speed above the planing mode engine speed, which is shown with a dashed line in FIG. 9 d . Once the sensed engine speed is below the planing mode engine speed (e.g., 6000 rpm) and the sensed throttle valve position is in a position substantially corresponding to idle speed operation (e.g., angle less than 5 degrees), the controller takes corrective action. In one arrangement, the corrective action comprises adjusting the ignition timing while, in another arrangement, the corrective action comprises increasing the air flow through an idle speed control passage. Of course, in some configurations, both actions can be taken simultaneously or in seriatim. The corrective action (the timing of which is indicated by the letters d and f in FIG. 9) decreases the rate of engine deceleration which allows the fuel injection control to better reflect the actual engine speed. In fact, the fuel injection amount preferably is incrementally reduced during the engine deceleration over a period of time, such as that indicated by the letter b in FIG. 9. Without taking a corrective action, the engine speed may continue to decrease until the engine stalls due to an overly rich fuel mixture (see period of time indicated by the letter c in FIG. 9 along with the accompanying dashed line). Eventually, a substantially constant but higher than idle engine speed will be attained for a predetermined period of time (i.e., the period of time indicated by the letter e in FIG. 9). After the predetermined period of time has elapsed, the corrective action is ended and the engine speed is allowed to further decrease to the desired idle speed. Thus, the routines of FIGS. 7 and 8 both return the engine to a predetermined idle speed within a desirably short period of time, which is indicated by the letter g in FIG. 9 while substantially reducing the likelihood of engine stall.  
         [0084]    With reference now to FIG. 10, another control routine is disclosed therein. In general, the control routine of FIG. 10 sets a desired engine idle speed depending at least in part on engine temperature and varies the ignition timing to achieve and/or to maintain that engine speed. With reference to FIG. 10, the illustrated routine starts and proceeds to an operation block P 20  where the engine temperature is measured. The routine continues to an operation block P 21  where an idle speed C is determined and set based upon the sensed engine temperature. The routine then continues to a decision block P 22  in which the sensed engine speed is compared to the set idle speed C. If the engine speed is less than the set idle speed C, then the routine moves to an operation block P 23  where the ignition timing is advanced in order to raise the engine speed and the routine then repeats.  
         [0085]    On the other hand, if the engine speed is not less than the set idle speed C, then the routine continues to a further decision block P 24  where the routine determines if the engine speed is greater than the set idle speed C. If the sensed engine speed is greater than the set idle speed C, then the routine proceeds to an operation block P 25  where the ignition timing is retarded in order to lower the engine speed and the routine then repeats.  
         [0086]    As illustrated, if the sensed engine speed is the same (i.e., within a preset range or identical to) the set idle speed C, then the routine repeats without adjusting the ignition timing.  
         [0087]    It is to be noted that the control systems described above may be in the form of a hard wired feedback control circuit in some configurations. Alternatively, the control systems may be constructed of a dedicated processor and memory for storing a computer program configured to perform the steps described above in the context of the flowcharts. Additionally, the control systems may be constructed of a general purpose computer having a general purpose processor and memory for storing the computer program for performing the routines. Preferably, however, the control systems are incorporated into the ECU  110 , in any of the above-mentioned forms.  
         [0088]    Although the present invention has been described in terms of a certain preferred embodiments, other embodiments apparent to those of ordinary skill in the art also are within the scope of this invention. Thus, various changes and modifications may be made without departing from the spirit and scope of the invention. For instance, various steps within the routines may be combined, separated, or reordered. In addition, some of the indicators sensed (e.g., engine speed and throttle position) to determine certain operating conditions (e.g., rapid deceleration) can be replaced by other indicators of the same or similar operating conditions. Moreover, not all of the features, aspects and advantages are necessarily required to practice the present invention. Accordingly, the scope of the present invention is intended to be defined only by the claims that follow.