Abstract:
A watercraft has an engine that is controlled to reduce the likelihood of engine damage when the watercraft engine speed is rapidly increased due to a lack of load on the propulsion unit. The engine is controlled by a method that detects engine speed and reduces the power output of the engine by varying degrees depending on the speed of the engine relative to plural predetermine speeds.

Description:
PRIORITY INFORMATION 
     This application is based on and claims priority to Japanese Patent Applications No. 2001-112641, filed Apr. 11, 2001, and No. 2001-288522, filed Sep. 21, 2001 the entire contents of which is hereby expressly incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present application generally relates to an engine control arrangement for a watercraft, and more particularly relates to an engine management system that prevents engine damage due to excessive engine speeds. 
     DESCRIPTION OF THE RELATED ART 
     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, watercraft may leave the water at speed due to waves, thus causing sudden decreased load on the propulsion unit, which can raise the engine RPM to a damaging speed. 
     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. The transition mode occurs between the displacement mode and the planing mode and involves the range of watercraft speeds between the planing and displacement modes. 
     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, increasing the likelihood that the propulsion unit will leave the water. 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 likelihood of air entering the propulsion unit is dramatically decreased. 
     One way of protecting the engine against over-revving is to limit the spark plugs from firing, allowing the engine to slow down. In two cycle engines since the spark plugs are fired every stroke, if one firing cycle of a spark plug is stopped in order to slow down the engine, engine smoothness is not significantly compromised. However, in a four cycle engine the spark plugs are fired every second stroke, so when the firing of a spark plug is omitted a noticeable compromise in engine smoothness occurs. Additionally, in any exhaust system where an exhaust catalyst is used, the exhaust catalyst may be damaged due to unburned fuel entering the exhaust system since the fuel injectors continue to operate when the ignition spark is interrupted. 
     SUMMARY OF THE INVENTION 
     Accordingly, an engine control arrangement has been developed to better control engine speed during a decreased load on the propulsion unit in order to prevent engine damage as well as maintaining a smooth ride. In addition, the engine control arrangement can be configured to maintain a safe engine speed by controlling the fuel injection to varying individual cylinders or to all cylinders gradually. 
     Thus, one aspect of the present invention is directed to a method of controlling a marine engine associated with a watercraft. The method includes sensing a first engine speed and comparing the first sensed engine speed with a first predetermined speed. Fuel supply to the engine is reduced by a first delivery amount if the first sensed engine speed is above the first predetermined engine speed. The method also includes sensing a second engine speed after reducing fuel delivery by a first fuel amount and restoring fuel delivery by the first fuel amount if the second sensed engine speed is below a second predetermined engine speed that is greater than the first predetermined engine speed. 
     One aspect of the invention includes the realization that there are operating conditions under which a speed-limiting device can cut engine power when the engine exceeds a first speed, then restore engine power before the engine speed falls below the first speed, without over-revving the engine. This control scenario can allow the engine to operate at an elevated engine speed during a period of reduced load, such as for example but without limitation, when the watercraft jumps slightly out of the water at high speed. By allowing the engine to operate at the elevated speed, the re-entry of the watercraft into the water can be more smooth. 
     Another aspect of the present invention is directed to a watercraft comprising a hull and an engine disposed within the hull. The engine includes an engine body defining plural cylinders. An engine speed sensor is configured to detect a speed of the engine. The watercraft also includes a controller connected to the engine speed sensor and configured to control a power output of the engine. The controller is configured to detect a first engine speed and to reduce the power output of the engine if the first engine speed is greater than a first predetermined engine speed. Additionally, the controller is configured to detect a second engine speed, and restore the power output of the engine if the second engine speed is less than a second predetermined engine speed, which is greater than the first predetermined engine speed. 
     Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing features, aspects, and advantages of the present invention will now be described with reference to the drawings of a preferred embodiment that is intended to illustrate and not to limit the invention. The drawings comprise fifteen figures in which: 
     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; 
     FIG. 2 is a top plan view of the watercraft of FIG. 1; 
     FIG. 3 is a front, starboard, and top perspective view of the engine removed from the watercraft illustrated in FIG. 1; 
     FIG. 4 is a front, port, and top perspective view of the engine removed from the watercraft illustrated in FIG. 1; 
     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; 
     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; 
     FIG. 7 is a cross-sectional view of the induction system of the engine. Portions of the intake manifold are illustrated partially in section; 
     FIG. 8 is a block diagram showing a control routine arranged and configured in accordance with certain features, aspects and advantages of the present invention; 
     FIG. 9 is a block diagram showing another control routine arranged and configured in accordance with certain features, aspects and advantages of the present invention; 
     FIG. 10 a  is a diagram of a graph illustrating engine speed characteristics during a small jump out of the water of a watercraft; 
     FIG. 10 b  is a diagram of a graph illustrating engine speed characteristics during a medium jump out of the water of a watercraft; 
     FIG. 10 c  is a diagram of a graph illustrating engine speed characteristics during a large jump out of the water of a watercraft; 
     FIG. 11 a  is a diagram illustrating a procedure for a fuel injection cut-off sequence arranged and configured in accordance with certain features, aspects and advantages of the present invention; and 
     FIG. 11 b  is a diagram illustrating another procedure for a fuel injection cutoff sequence arranged and configured in accordance with certain features, aspects and advantages of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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 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 with 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. 
     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 . 
     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. 
     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. 
     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). 
     The seat  28  extends rearwardly from a portion just rearward of the bow portion  30 . The seat  28  is disposed atop a pedestal  35  defined by the deck  18  (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. 
     Foot areas  36  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  36  are formed generally flat but may be inclined toward a suitable drain configuration. 
     The seat  28  preferably is configured to close an access opening  38  formed within the pedestal  35 . The access opening  38  generally provides suitable access to the internal cavity  20  and, in the illustrated arrangement, to the engine  12 . Thus, when the seat  28  is removed from the pedestal  35 , the engine  12  can be accessed through the opening  38 . In the illustrated embodiment, the upper hull section  18  or pedestal  35  also encloses a storage box  40  that is disposed under the seat  28 . 
     A fuel tank  42  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  42  with a fuel inlet port positioned at a top surface of the bow  30  of the upper hull section  18 . A closure cap  44  (see FIG. 2) closes the fuel inlet port to inhibit water infiltration. 
     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). In general, the engine compartment is defined within the cavity  20  by a forward and rearward bulkhead. Other configurations, however, are possible. 
     A pair of air ducts  46  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. 
     A jet pump unit  48  propels the illustrated watercraft  10 . Other types of marine drives can be used depending upon the application. The jet pump unit  48  preferably is disposed within a tunnel  50  formed on the underside of the lower hull section  16 . The tunnel  50  has a downward facing inlet port  52  opening toward the body of water. A jet pump housing  54  is disposed within a portion of the tunnel  50 . Preferably, an impeller (not shown) is supported within the jet pump housing  54 . 
     An impeller shaft  56  extends forwardly from the impeller and is coupled with a crankshaft  58  of the engine  12  by a suitable coupling device  60 . The crankshaft  58  of the engine  12  thus drives the impeller shaft  56 . The rear end of the housing  54  defines a discharge nozzle  61 . A steering nozzle  62  is affixed proximate the discharge nozzle  61 . The steering nozzle  62  can be pivotally moved about a generally vertical steering axis. The steering nozzle  62  is connected to the handle bar  32  by a cable or other suitable arrangement so that the rider can pivot the nozzle  62  for steering the watercraft. 
     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  64  with four cylinder bores  66  formed side by side. 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. Many orientations of the engine are also possible (e.g., with a transversely or vertically oriented crankshaft). 
     With continued reference to FIG. 5, a piston  68  reciprocates in each of the cylinder bores  66  formed within the cylinder block  64 . A cylinder head member  70  is affixed to the upper end of the cylinder block  64  to close respective upper ends of the cylinder bores  66 . The cylinder head member  70 , the cylinder bores  66  and the pistons  68  together define combustion chambers  72 . 
     A lower cylinder block member or crankcase member  74  is affixed to the lower end of the cylinder block  64  to close the respective lower ends of the cylinder bores  66  and to define, in part, a crankshaft chamber. The crankshaft  58  is journaled between the cylinder block  64  and the lower cylinder block member  74 . The crankshaft  58  is rotatably connected to the pistons  68  through connecting rods  76 . Preferably, a crankshaft speed sensor  77  is disposed proximate the crankshaft to output a signal indicative of engine speed. In some configurations, the crankshaft speed sensor  77  is formed, at least in part, with a flywheel magneto. The speed sensor  77  also can output crankshaft position signals in some arrangements. 
     The cylinder block  64 , the cylinder head member  70  and the crankcase member  74  together generally define an engine block of the engine  12 . The engine  12  preferably is made of an aluminum-based alloy. 
     Engine mounts  78  preferably extend from both sides of the engine  12 . The engine mounts  78  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  78  so that the engine  12  is greatly inhibited from conducting vibration energy to the hull section  16 . 
     The engine  12  preferably includes an air induction system to guide air to the combustion chambers  72 . In the illustrated embodiment, the air induction system includes four air intake ports  80  defined within the cylinder head member  70 . The intake ports  80  communicate with the four combustion chambers  72 , respectfully. Other numbers of ports can be used depending upon the application. 
     Intake valves  82  are provided to open and close the intake ports  80  such that flow through the ports  80  can be controlled. A camshaft arrangement that can be used to control the intake valves  82  is discussed below. 
     The air induction system also includes an air intake box  84  for smoothing intake airflow and acting as an intake silencer. The intake box  84  in the illustrated embodiment is generally rectangular and, along with an intake box cover  86 , defines a plenum chamber  88 . The intake box cover  86  can be attached to the intake box  84  with a number of intake box cover clips  90  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. 
     With reference now to FIG. 5, in the illustrated arrangement, air is introduced into the plenum chamber  88  through a pair of airbox inlet ports  92  and a filter  94 . With reference to FIG. 6, the illustrated air induction system preferably also includes an idle speed control device (ISC)  96  that may be controlled by an Electronic Control Unit (ECU)  98  discussed in greater detail below. 
     In one advantageous arrangement, the ECU  98  is a microcomputer that includes a micro-controller having a CPU, a timer, RAM, and ROM. Of course, other suitable configurations of the ECU also can be used. Preferably, the ECU  98  is configured with or capable of accessing various maps to control engine operation in a suitable manner. 
     In general, the ISC device  96  comprises an air passage  100  that bypasses a throttle valve assembly  102 . Air flow through the air passage  100  of the ISC device  96  preferably is controlled with a suitable valve  104 , which may be 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 is discussed below. 
     Throttle bodies  106  slant downwardly toward the port side relative to the center axis of the engine  12 . Respective top ends  108  of the throttle bodies  106 , in turn, open upwardly within the plenum chamber  88 . Air in the plenum chamber  88  thus is drawn through the throttle bodies  106 , through individual intake passages  110  and the intake ports  80  into the combustion chambers  72  when negative pressure is generated in the combustion chambers  72 . The negative pressure is generated when the pistons  68  move toward the bottom dead center position from the top dead center position during the intake stroke. 
     With reference to FIG. 7, a throttle valve position sensor  112  preferably is arranged proximate the throttle valve assembly  102  in the illustrated arrangement. The sensor  112  preferably generates a signal that is representative of either absolute throttle position or movement of the throttle shaft. Thus, the signal from the throttle valve position sensor  112  corresponds generally to the engine load, as may be indicated by the degree of throttle opening. In some applications, a manifold pressure sensor  114  can also be provided to detect engine load. Additionally, an induction air temperature sensor  116  can be provided to detect induction air temperature. The signal from the sensors  112 ,  114 ,  116  can be sent to the ECU  98  via respective data lines. These signals, along with other signals, 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. 
     The engine  12  also includes a fuel injection system which preferably includes four fuel injectors  118 , each having an injection nozzle exposed to the intake ports  80  so that injected fuel is directed toward the combustion chambers  72 . 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. 
     With reference again to FIG. 6, fuel is drawn from the fuel tank  42  by a fuel pump  120 , which is controlled by the ECU  98 . The fuel is delivered to the fuel injectors  118  through a fuel delivery conduit  122 . A fuel return conduit  124  also is provided between the fuel injectors  118  and the fuel tank  42 . Excess fuel that is not injected by the fuel injector  118  returns to the fuel tank  42  through the conduit  124 . The flow generated by the return of the unused fuel from the fuel injectors aids in cooling the fuel injectors. 
     In operation, a predetermined amount of fuel is sprayed into the intake ports  80  via the injection nozzles of the fuel injectors  118 . The timing and duration of the fuel injection is dictated by the ECU  98  based upon any desired control strategy. In one presently preferred configuration, the amount of fuel injected is based upon the sensed throttle valve position and the sensed manifold pressure, depending on the state of engine operation. The fuel charge delivered by the fuel injectors  118  then enters the combustion chambers  72  with an air charge when the intake valves  82  open the intake ports  80 . 
     The engine  12  further includes an ignition system. In the illustrated arrangement, four spark plugs  128  are fixed on the cylinder head member  70 . The electrodes of the spark plugs  128  are exposed within the respective combustion chambers  72 . The spark plugs  128  ignite an air/fuel charge just prior to, or during, each power stroke, preferably under the control of the ECU  98  to ignite the air/fuel charge therein. 
     The engine  12  further includes an exhaust system  130  to discharge burnt charges, i.e., exhaust gases, from the combustion chambers  72 . In the illustrated arrangement, the exhaust system  130  includes four exhaust ports  132  that generally correspond to, and communicate with, the combustion chambers  72 . The exhaust ports  132  preferably are defined in the cylinder head member  70 . Exhaust valves  134  preferably are provided to selectively open and close the exhaust ports  132 . A suitable exhaust cam arrangement, such as that described below, can be provided to operate the exhaust valves  134 . 
     A combustion condition or oxygen sensor  136  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  136  preferably is delivered to the ECU  98 . The oxygen sensor  136  can be disposed within the exhaust system at any suitable location. In the illustrated arrangement, the oxygen sensor  136  is disposed proximate the exhaust port  132  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. 
     With reference now to FIG. 3, the illustrated exhaust system  130  preferably includes two small exhaust manifolds  138 ,  140  that each receive exhaust gases from a pair of exhaust ports  132  (i.e., a pair of cylinders). The respective downstream ends of the exhaust manifolds  138 ,  140  are coupled with a first unitary exhaust conduit  142 . The first unitary conduit  142  is further coupled with a second unitary exhaust conduit  144 . The second unitary conduit  144  is coupled with an exhaust pipe  146  at a location generally forward of the engine  12 . 
     The exhaust pipe  146  extends rearwardly along a port side surface of the engine  12 . The exhaust pipe  146  is connected to a water-lock  148  proximate a forward surface of the water-lock  148 . With reference to FIG. 2, a discharge pipe  150  extends from a top surface of the water-lock  148 . The discharge pipe  150  bends transversely across the center plane and rearwardly toward a stem of the watercraft. Preferably, the discharge pipe  150  opens at a stem of the lower hull section  16  in a submerged position. As is known, the water-lock  148  generally inhibits water in the discharge pipe  150  or the water-lock itself from entering the exhaust pipe  146 . 
     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 expected 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. 
     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  152  can be provided around portions of the cylinder block  64  and the cylinder head member  70  (see FIG.  6 ). 
     In some applications, the exhaust system  130  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. 
     An engine coolant temperature sensor  154  preferably is positioned to sense the temperature of the coolant circulating through the engine. Of course, the sensor  154  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. 
     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  130 . 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  130  from the air induction system. In one arrangement of the secondary air supply system, a secondary air supply device  156  is disposed next to the cylinder head member  70  on the starboard side. The air supply device  156  defines a generally closed cavity and contains a control valve in the illustrated arrangement. Air supplied from the air supply device  156  passes directly to the exhaust system  130  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. 
     With reference to FIGS. 5 and 6, the engine  12  preferably has a valve cam mechanism for actuating the intake and exhaust valves  82 ,  134 . In the illustrated embodiment, a double overhead camshaft drive is employed. That is, an intake camshaft  158  actuates the intake valves  82  and an exhaust camshaft  160  separately actuates the exhaust valves  134 . The intake camshaft  158  extends generally horizontally over the intake valves  82  from fore to aft, and the exhaust camshaft  160  extends generally horizontally over the exhaust valves  134  also from fore to aft. 
     Both the intake and exhaust camshafts  158 ,  160  are journaled in the cylinder head member  70  in any suitable manner. A cylinder head cover member  162  extends over the camshafts  158 ,  160 , and is affixed to the cylinder head member  70  to define a camshaft chamber. The secondary air supply device  156  is preferably affixed to the cylinder head cover member  162 . Additionally, the air supply device  156  is desirably disposed between the intake air box and the engine  12 . 
     The intake camshaft  158  has cam lobes each associated with the respective intake valves  82 , and the exhaust camshaft  160  also has cam lobes associated with respective exhaust valves  134 . The intake and exhaust valves  82 ,  134  normally close the intake and exhaust ports  80 ,  132  by a biasing force of springs. When the intake and exhaust camshafts  158 ,  160  rotate, the cam lobes push the respective valves  82 ,  134  to open the respective ports  80 ,  132  by overcoming the biasing force of the spring. Air enters the combustion chambers  72  when the intake valves  82  open. In the same manner, the exhaust gases exit from the combustion chambers  72  when the exhaust valves  134  open. 
     The crankshaft  58  preferably drives the intake and exhaust camshafts  158 ,  160 . The respective camshafts  158 ,  160  have driven sprockets affixed to ends thereof while the crankshaft  58  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  58  rotates, the drive sprocket drives the driven sprockets via the timing chain, and thus the intake and exhaust camshafts  158 ,  160  also rotate. 
     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  164 , as illustrated in FIGS. 3 and 4. 
     An oil delivery pump is provided within a circulation loop to deliver the oil in the reservoir  164  through an oil filter  166  to the engine portions that are to be lubricated, for example, but without limitation, the pistons  68  and the crankshaft bearings (not shown). The crankshaft  58  or one of the camshafts  158 , 160  preferably drives the delivery and return pumps. 
     In order to determine appropriate engine operation control scenarios, the ECU  98  preferably uses control maps and/or indices stored within the ECU  98  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  112 , the manifold pressure sensor  114 , the engine coolant temperature sensor  154 , the oxygen (O 2 ) sensor  136 , and a crankshaft speed sensor  77 . 
     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 . 
     During engine operation, ambient air enters the internal cavity  20  defined in the hull  14  through the air ducts  44 . As seen in FIGS. 5,  6 , and  7 , the air is then introduced into the plenum chamber  88  defined by the intake box  84  through the air inlet ports  92  and drawn into the throttle bodies  106 . The air filter element  94 , which preferably comprises a water-repellent element and an oil resistant element, filters the air. The majority of the air in the plenum chamber  88  is supplied to the combustion chambers  72 . The throttle valves  102  in the throttle bodies  106  regulate an amount of the air permitted to pass to the combustion chambers  72 . The opening angles of the throttle valves  102 , and thus, the airflow across the throttle valves  102 , can be controlled by the rider with the throttle lever  34 . The air flows into the combustion chambers  72  when the intake valves  82  open. At the same time, the fuel injectors  118  spray fuel into the intake ports  80  under the control of ECU  98 . Air/fuel charges are thus formed and delivered to the combustion chambers  72 . 
     The air/fuel charges are fired by the spark plugs  128  under the control of the ECU  98 . The burnt charges, i.e., exhaust gases, are discharged to the body of water surrounding the watercraft  10  through the exhaust system  130 . A relatively small amount of the air in the plenum chamber  88  is supplied to the exhaust system  130  so as to aid in further combustion of any unburned fuel remaining in the exhaust gases. 
     The combustion of the air/fuel charges causes the pistons  68  to reciprocate and thus causes the crankshaft  58  to rotate. The crankshaft  58  drives the impeller shaft  56  and the impeller rotates in the hull tunnel  50 . Water is thus drawn into the tunnel  50  through the inlet port  52  and then is discharged rearward through the steering nozzle  62 . The rider steers the nozzle  62  by the steering handle bar  32 . The watercraft  10  thus moves as the rider desires. 
     With reference to FIG. 8, 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  170  is configured to control operation of the fuel injection based on engine speed to prevent over-revving engine damage. As shown in FIG. 8, the control routine begins and moves to a first decision block P 2 . In the illustrated embodiment, the routine  170  can start as soon as a rider attempts to start the engine  12 , for example as soon as the start button is activated. However, it is to be understood that the routine  170  can start at any time. 
     In decision block P 2 , the engine speed R is compared to a predetermined initial engine speed A. Preferably, the predetermined initial engine speed A is an engine speed that is higher than an engine speed that corresponds to a steady-state full throttle/top speed operation where the intake duct of the jet propulsion unit is completely submerged. If the engine speed R is determined to be not greater than or equal to speed A, the program moves to the operation block P 4 . 
     In the operation block P 4 , normal fuel injection operation is established for all cylinders of engine  12 . Preferably, the control routine  170  returns to the beginning and repeats as long as the engine is running. 
     If however, at the operation block P 2 , the sensed engine speed R is not greater than or equal to A, the control routine  170  moves to operation block P 6  where the fuel injection is stopped for a single cylinder, thereby disabling that cylinder. Stopping fuel injection for a single cylinder reduces the total power output of the engine  12  by a first degree. In other words, the power output of the engine is reduced to a first state of reduced power output. Under certain conditions, such a reduction in power output will result in a reduction in engine speed. However, under other conditions, discussed in greater detail below, the engine speed may not fall. 
     After the operation block P 6 , the control routine  170  then proceeds to a decision block P 8  where it is determined if the engine has rotated N times (N corresponding to the number of revolutions needed to complete a combustion cycle, for a four cycle, N=2). If the engine has not rotated N times then the control routine  170  returns to P 8  until the number of engine revolutions N is achieved. 
     If however, at the decision block P 8 , the engine has rotated N times, the control routine  170  moves to decision block P 10  where it determines if the engine speed R is greater than or equal to B. The second predetermined engine speed B is an engine speed that is higher than engine speed A. 
     If, at decision block P 10 , it is determined that the engine speed R is greater than or equal to the predetermined engine speed B, the control routine  170  moves to operation block P 12  where the fuel injection is stopped for an additional cylinder. Stopping the fuel injection for an additional cylinder will further reduce the total power output of the engine  12 , by a second degree. In other words, the power output of the engine is reduced to a second state of reduced power. Under certain conditions, such a further reduction in power output can cause the engine speed R to fall. However, under other conditions, discussed in greater detail below, the engine speed R may not fall. The control routine  170  then moves to decision block P 16 . 
     If however, in decision block P 10 , it is determined that the engine speed R is not greater than or equal to a second predetermined engine speed B, the control routine  170  moves to operation block P 14 . 
     At the operation block P 14 , the control routine  170  resumes fuel injection to the cylinder disabled at the operation block P 6 . Thus, the power output of the engine  12  is increased by a degree. In other words, the power output of the engine  12  is restored or increased by the first degree, back to the normal power output. After the operation block P 14 , the control routine  170  moves to the decision block P 16 . 
     In decision block P 16 , the control routine  170  again determines if an engine speed R is greater than or equal to the first predetermined engine speed A. If the engine speed R is not greater than or equal to the first predetermined engine speed A, the control routine  170  moves to operation block P 4  where normal fuel injection operation is resumed for all cylinders. 
     If however, in decision block P 16 , the engine speed R is greater than or equal to the first predetermined engine speed A, the control routine  170  moves to decision block P 18  where the engine speed R is compared to a third predetermined engine speed C, which is higher than the first and second predetermined engine speeds. 
     If in the decision block P 18  the engine speed R is found to be greater or equal to the third predetermined engine speed C the control routine  170  moves to operation block P 20  where the fuel injection is stopped for all cylinders. Stopping the fuel injection for all cylinders lowers the engine speed under any condition the watercraft  10  is likely to experience in operation. 
     If however, in decision block P 18  the engine speed R is not greater than or equal to the third predetermined engine speed, the control routine  170  moves to decision block P 8  and repeats. 
     With reference now to FIG. 9, a modification of the control routine  170  is shown therein and referred to by the reference numeral  172 . The control routine  172  is configured to control operation of the fuel injection based on engine speed. As shown in FIG. 9, the control routine begins and moves to a first decision block P 30 . In the illustrated embodiment, the routine  172  can start as soon as a rider attempts to start the engine  12 , for example as soon as the start button is activated. However, it is to be understood that the routine  172  can start at any time. 
     In decision block P 30 , the engine speed R is compared to the first predetermined engine speed A. If the engine speed R is not greater than or equal to speed A, the program moves to the operation block P 32 . 
     In the operation block P 32 , normal fuel injection operation is continued or reestablished for all cylinders of engine  12 . Preferably, the control routine  172  returns to the beginning and repeats as long as the engine is running. 
     If however in the decision block P 30 , the sensed engine speed R is not greater than or equal to A, the control routine  172  moves to operation block P 34  where the fuel injection for all cylinders is decreased at a predetermined rate. For example, the control routine  172  can decrease the fuel injection to all of the cylinders by 20%. i.e., for five fuel injection cycles, one is skipped. This method of reducing fuel injection is explained below in greater detail with reference to FIGS. 11 a  and  11   b . Under certain conditions, reducing fuel injection as such will cause the engine speed R to fall. However, under other conditions, discussed below in greater detail, the engine speed R may not fall. After the operation block P 34 , the control routine  170  moves to a decision block P 36 . 
     At the decision block P 36  it is determined if the engine has rotated N times (N corresponding to the number of revolutions needed to complete a combustion cycle, e.g. for a four cycle engine, N=2). If the engine has not rotated N times then the control routine  172  returns to P 36  until the number of engine revolutions N is achieved. 
     If however, the engine has rotated N times, the control routine  172  moves to decision block P 38  where it determines if the engine speed R is greater than or equal to the second predetermined engine speed B. If it is determined that the engine speed R is greater than or equal to the predetermined engine speed-B, the control routine  172  moves to an operation block P 40 . 
     At the operation block P 40 , the fuel injection is further decreased for all cylinders by a predetermined rate. For example, the control routine  172  can further decrease the fuel injection for all of the cylinders by an additional 20%, resulting in a 40% reduction in fuel injection relative to the normal fuel injection scenario. After the operation block P 40 , the control routine  172  then moves to a decision block P 42 . 
     If however, in decision block P 38  it is determined that the engine speed R is not greater than or equal to a second predetermined engine speed B, the control routine  172  moves to operation block P 48 , where the rate of fuel injection cutoff is decreased. For example, if the fuel injection had been decreased by 20% in operation block P 34 , fuel injection can be increased by 20%. The control routine then moves to decision block P 42 . 
     In the decision block P 42 , the control routine  172  again determines if an engine speed R is greater than or equal to the first predetermined engine speed A. In decision block P 42 , if the engine speed R is not greater than or equal to the first predetermined engine speed A, the control routine  172  moves to operation block P 32  where normal fuel injection operation is established for all cylinders. 
     If however, in decision block P 42 , the engine speed R is greater than or equal to the first predetermined engine speed A, the control routine  172  moves to decision block P 44  where the engine speed R is compared to the third predetermined engine speed C. 
     If, in the decision block P 44 , the engine speed R is found to be greater or equal to the third predetermined engine speed C the control routine  172  moves to operation block P 46  where the fuel injection is stopped for all cylinders. Stopping the fuel injection for all cylinders lowers the engine speed in any condition in which the watercraft  10  is likely to be operated. 
     If however, in decision block P 44  the engine speed R is not greater than or equal to the third predetermined engine speed threshold the control routine moves to decision block P 36  and continues to repeat the control routine steps. 
     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. 
     With reference to FIGS. 10 a ,  10   b , and  10   c , graphs illustrating engine speed characteristics during various operational conditions of the watercraft  10 . In particular, FIGS. 10 a ,  10   b , and  10   c  illustrate a relationship between engine speed (vertical axis) and time (horizontal axis) when the watercraft jumps out of the water sufficiently to cause air to be drawn into the jet pump. In each figure, a solid line represents the behavior of the engine  12  during a small jump (FIG. 10 a ), a medium jump (FIG. 10 b ), and a large jump (FIG. 10 c ). Additionally, each of these figures includes a dashed line representing the theoretical behavior of a watercraft engine with no rev-limiter. 
     In the FIGS. 10 a ,  10   b , and  10   c , a steady state, constant, full throttle engine speed  198  is illustrated. At this steady state engine speed the jet pump unit  48  is experiencing a consistent load. However this engine speed  198  is not the highest allowable engine speed. At an engine speed range above the steady state engine speed  198 , the present invention is designed to limit higher engine speeds in proportion to a magnitude in reduction of load, such as that caused when the watercraft jumps partially or completely out of the water. 
     Three predetermined engine speeds, A, B, and C are used to as reference so as to create a proportional rev-limiting response in order to maintain a smooth ride. The first predetermined engine speed A represents an engine speed that is slightly higher than the optimal engine speed  198 . At the detection of the first predetermined engine speed A the control system starts to limit the engine speed. A second predetermined engine speed B is slightly above the first predetermined engine speed A. A third predetermined engine speed C represents an engine speed that can be too high for the engine to operate properly. The predetermined engine speed C corresponds to an engine speed in which the control system can rapidly lower the engine speed to an engine speed where the engine operates more efficiently. 
     With reference to FIG. 10 a  and the control routines  170  and  172 , the engine speed of the watercraft  10  during a small jump with reference to time is shown. In time increment  174 , an engine speed increase is shown approaching the first predetermined engine speed A. With reference to P 2  and P 30 , when the engine speed reaches the first predetermined engine speed A at a point  175 , the power output of the engine is lowered. Under this condition, where only a small amount of air enter the jet pump unit  48 , reducing the power output of the engine  12  to the first reduced output state is sufficient to cause the engine speed to drop below the speed A. In time increment  176 , a controlled engine speed decrease can by seen where the engine speed is initially brought down for a period of time N, which corresponds to the operation performed in the operation block P 8 , and then resumes to optimal operating speed. 
     With reference to FIG. 10 b  and the control routines  170  and  172 , the engine speed of the watercraft during a medium jump with reference to time is shown. In time increment  178 , an initial engine speed increase can be seen. As seen in time increment  180 , this speed increase reaches above the first predetermined speed A at point  179 . Thus, as dictated by operation block P 6  and P 34 , the power output of the engine  12  is initially reduced. However, because of the size of this jump, and the accompanying drop in load on the engine, the engine speed does not stop increasing until it reaches a speed between the predetermined speeds B and C. 
     At the end of the time period  180 , after the engine has rotated N times, it is determined that the engine speed is above speed B. Thus, as dictated by the operation blocks P 12  and P 40 , the power output of the engine  12  is further reduced, i.e., reduced to a second state of reduced power, such as for example but without limitation, two cylinders disabled or fuel injection reduced by 40%. As represented in FIG. 10 b , this power reduction is sufficient to cause the engine speed to fall. As illustrated at the beginning of the time period  182 , the engine speed falls to a speed between the speeds A and B. 
     At the end of the time period  182 , the routines  170 ,  172  then return to the decision blocks P 10  and P 38  respectively. Because the engine speed is below speed B, power output is increased by a degree. In this case, the power output is restored to the first state of reduced power output, for example but without limitation, only one cylinder disabled or fuel injection reduced by 20%. Thus, due to the magnitude of this jump, the engine speed rises to speed between the speeds B and C. 
     As the routines  170 ,  172  repeat, the engine  12  is allowed to operate at a speed above the speed A. Thus, as the jet pump unit is re-loaded, the engine speed does not drop abruptly. As noted above, abrupt drops in engine speed can make the operator and passengers uncomfortable. 
     FIG. 10 c  illustrates the behavior of the control routines  170  and  172  and their affect on the engine speed of the watercraft during a large jump. During time increments  188 ,  190 ,  192 ,  194 ,  196 , the engine speed fluctuates due to a prolonged lack of engine load by the absence of water in the jet pump unit  48 . 
     For example, as the engine speed rises above speed A, at the end of time period  188  (point  200 ), the control routines  170 ,  172  reduce power output at operation blocks P 6  and P 34 , respectively. However, due to the magnitude of this jump, the engine speed does not fall. By the time the engine speed is sensed again at decision blocks P 10  and P 38 , after the time delay produced by decision blocks P 8  and P 36  (the end of time period  190 ), the engine speed has already exceeded speed C (point  202 ). Thus, the routines quickly reach operation blocks P 20  and P 46 , cutting off all power. 
     Because the engine speed is considerable, the engine continues to rotate as it slows. As the routines reach decision block P 16  and  942 , respectively, the engine speed falls to a speed below speed A (point  204 ). Thus, normal fuel injection, and thus, full power output are restored (operation blocks P 4 , P 32 ). However, because the jet pump unit  46  is not loaded, the cycle repeats until the jet pump unit  46  is re-loaded. 
     With reference to FIGS. 11 a  and  11   b , procedures for a fuel injection cut-off sequence are shown. Both procedures represent ways to regulate a fuel injection cut-off sequence, which preserves a smooth-feeling operation for the watercraft operator. As shown in FIG. 11 a , a fuel injection sequence follows from left to right. Numbers represent which cylinder into which the fuel is being injected. A zero indicates that a normal fuel injection cycle is performed for the corresponding cylinder, and an X represents fuel injection cut-off for that cylinder. FIG. 11 a  shows a fuel injection cutoff sequence where the same cylinder is being repeatedly deprived of fuel. As such, FIG. 11 a  corresponds to fuel injection being cut-off for one cylinder of the engine  12 . 
     Such a reduction of fuel injection can also be expressed as a percentage. For example, when fuel injection to one cylinder is stopped in a four cylinder engine, one fuel injection cycle is skipped for every four fuel injection cycles of the normal mode. Thus, in the scenario illustrated in FIG. 11 a , fuel injection has been reduced by 25%. 
     As shown in FIG. 11 b , a fuel injection sequence again follows from left to right. Numbers represent which cylinder into which the fuel is being injected. A zero indicates that a normal fuel injection cycle is performed for the corresponding cylinder, and an X represents fuel injection cut-off for that cylinder. FIG. 11 b  shows a fuel injection cut-off sequence where each cylinder is being sequentially deprived of fuel. As such, FIG. 11 b  corresponds to fuel injection being cut-off for one cylinder per fuel injection cycle of the engine  12  in an alternating sequence. 
     Such a reduction of fuel injection can also be expressed as a percentage. For example, when fuel injection to one cylinder per fuel injection cycle is stopped in an alternating sequence in a four cylinder engine, one fuel injection cycle is skipped for every five fuel injection cycles of the normal mode. Thus, in the scenario illustrated in FIG. 11 b , fuel injection has been reduced by 20%. An alternating sequential fuel injection cut off prevents damage associated with repeated cylinder disablement. 
     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. 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.