Abstract:
An engine control system and a method control the engine speed of a watercraft that is propelled by a stream of water generated by propulsion unit driven by an engine. The system and method detect whether the propulsion unit is generating the stream of water. The system and method limit the maximum engine speed to a first speed when the propulsion unit is generating the stream of water and limit the maximum engine speed to a second speed, lower than the first speed, when the propulsion unit is not generating the stream of water.

Description:
PRIORITY INFORMATION 
     This invention is based on Japanese Patent Application No. 2000-169273, filed Jun. 6, 2000, the entire contents of which is hereby expressly incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present application relates to an engine control arrangement for controlling a watercraft, and more particularly relates to an engine management system that controls engine speed in order to reduce noise. 
     2. Description of the Related Art 
     Watercraft, including personal watercraft and jet boats, are often powered by at least one internal combustion engine having an output shaft arranged to drive one or more water propulsion devices. Occasionally, engine revving is conducted out of the water in order to test the engine or to use exhaust pressure to drain salt water that has entered the engine during cruising. 
     Unfortunately, since there is no water resistance applied to the propulsion device when revving the engine out of the water, the engine speed may easily reach or exceed a maximum safe speed when the throttle is slightly applied, which causes extremely loud noise. 
     SUMMARY OF THE INVENTION 
     The present application is directed to an engine control arrangement of the type used to power a watercraft, which controls the engine speed and prevents the engine from revving too high when out of the water, thus preventing excessively loud noise. 
     One aspect of the preferred embodiments is an engine speed control system for a watercraft that is propelled by a stream of water generated by a propulsion unit driven by an engine. The engine control system comprises means for detecting whether the propulsion unit is generating a stream of water. The system also comprises a controller responsive to the means for detecting, the controller limiting the maximum engine speed to a first speed when the propulsion unit is generating the stream of water, the controller limiting the maximum engine speed to a second speed, lower than the first speed, when the propulsion unit is not generating the stream of water. 
     In one preferred embodiment of this first aspect, the means for detecting comprises a first sensor that senses ambient atmospheric pressure and a second sensor that senses a pressure responsive to the movement of the stream of water. The means for detecting compares the ambient atmospheric pressure and the pressure responsive to the movement of the stream of water to determine whether the stream of water is being generated by the propulsion unit. 
     In one particularly preferred embodiment, the propulsion unit includes an inlet that receives water, and the second sensor is positioned in the inlet such that the pressure sensed by the second sensor decreases with increasing water flow and increases with decreasing water flow. 
     In an alternative particularly preferred embodiment, the propulsion unit includes an outlet that conveys the stream of water generated by the propulsion unit, and the second sensor is positioned in the outlet such that the pressure sensed by the second sensor increases with increasing water flow and decreases with decreasing water flow. 
     In an alternative embodiment, the means for detecting comprises a sensor that responds to the speed of the watercraft to determine whether the stream of water is being generated by the propulsion unit. 
     In accordance with a particular aspect of the preferred embodiment, the controller reduces the engine speed to the second speed only after the controller determines that the propulsion unit is not generating the stream of water for a predetermined time duration. For example, the predetermined time duration is advantageously at least 5 seconds. 
     In one exemplary embodiment, the first speed is 7,000 revolutions per minute, and the second speed is 4,000 revolutions per minute. 
     A second aspect of the preferred embodiments is a method for reducing engine speed and thereby reducing engine noise of a watercraft propelled by a stream of water generated by a propulsion unit driven by an engine when the watercraft is out of the water. The method comprises sensing whether the watercraft is out of the water, controlling the engine speed to a first maximum speed when the watercraft is in the water, and controlling the engine speed to a second maximum speed when the watercraft is out of the water, the second maximum speed lower than the first maximum speed. 
     In one preferred embodiment of this second aspect, the sensing step comprises comparing a first pressure with a second pressure to determine whether water is flowing through the propulsion unit. In a particularly preferred embodiment, the first pressure is ambient atmospheric pressure, and the second pressure is determined by the flow of water through the propulsion unit. 
     In a first alternative of this particularly preferred embodiment. the second pressure is measured at an inlet to the propulsion unit, the second pressure decreasing with increasing flow of water and decreasing with increasing flow of water. 
     In a second alternative of this particularly preferred embodiment, the second pressure is measured at an outlet to the propulsion unit, the second pressure decreasing with decreasing flow of water and increasing with increasing flow of water. 
     In an alternative embodiment, the sensing step comprises sensing the speed of the watercraft to determine whether water is flowing through the propulsion unit. 
     In particular aspects of the method, the engine speed is controlled to the second speed only after the method determines that the propulsion unit is not generating the stream of water for a predetermined time duration. In an exemplary embodiment of the method, the predetermined time duration is at least 5 seconds. 
     In particular embodiments of the method, the first speed is 7,000 revolutions per minute, and the second speed is 4,000 revolutions per minute. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects of the preferred embodiment of the invention are described in detail below in connection with the accompanying drawings in which: 
     FIG. 1 is a side view of a personal watercraft of the type powered by an engine having an engine control arrangement in accordance with the present invention, the engine and other watercraft components positioned within the watercraft illustrated in phantom; 
     FIG. 2 is a cross-sectional end view of the watercraft taken along the line  2 — 2  of FIG. 1, illustrating the engine therein and a portion of the exhaust system with a catalyst in cross-section; 
     FIG. 3 is a cross sectional side view of the jet propulsion unit illustrating the pressure sensors therein; and 
     FIG. 4 id a block diagram showing a control routine constructed and operated in accordance with an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiment is an engine control arrangement for an engine of the type utilized to power a watercraft, including a personal watercraft or a jet boat. 
     FIG. 1 illustrates a watercraft  10  comprising a top portion or deck  12  and a lower portion  14 . A gunwale  16  defines the intersection of the deck  12  and the lower portion  14 . A cover  18  is provided in the front upper side of the deck  12 . A storage cover  20  is mounted on the forward side of the cover  18 . A fuel tank  22  (shown in phantom) is located in the lower portion  14 . 
     The rear portion of the deck  12  provides a seat base  24 . A seat  26  is positioned on the seat base  24 . A steering handle  28  is provided adjacent the seat  26  for use by a user in directing the watercraft  10 . 
     As illustrated in FIG. 2, a respective bulwark  30  extends upwardly along each side of the watercraft  10 . A respective footstep area  32 ,  34  is defined between the seat base  24  and each bulwark  30 . 
     As illustrated in FIGS. 1 and 2, the watercraft  10  includes an engine  36  positioned in an engine compartment  38 . The engine  36  is preferably a two-cylinder, two-cycle engine. The engine  36  may have as few as one, or more than two cylinders, as will be appreciated by one skilled in the art. 
     As illustrated in FIG. 2, the engine  36  is connected to the lower portion  14  via several engine mounts  40 . The mounts  40  are connected to upwardly extending supports  42 , which are connected to the lower portion  14  of the watercraft  10 . The engine  36  is preferably at least partially accessible through a maintenance opening  44  accessible by removing the seat  26 . 
     The engine  36  has a crankshaft  46  (see FIG. 2) which is in driving relation with an impeller shaft  48  (see FIG. 3) through a coupling  50  (see FIG.  1 ). The impeller shaft  48  rotationally drives a means for propelling water (e.g., an impeller  52 ) in a propulsion unit  54 , which unit extends out the stern portion of the watercraft  10 . 
     The propulsion unit  54  includes a propulsion passage  56  having an intake port (i.e., a water inlet  58 ). The water inlet  58  extends through the lower portion  14  of the watercraft  10 . The passage  56  also has an outlet  60  that has a discharge positioned within a nozzle  62 . The nozzle  62  is mounted for movement up and down and to the left and right, whereby the direction of the propulsion force for the watercraft  10  may be varied. 
     The engine  36  includes a cylinder block  64  having a cylinder head  66  connected thereto and cooperating therewith to define a combustion chamber  68  defined by cylinder wall  70  within the block  64  and by a recessed area  72  in the cylinder head  66 . A piston  74  is movably mounted in the combustion chamber  68 , and is connected to a crankshaft  46  via a connecting rod  76 , as is well known in the art. A second combustion chamber (not shown) is positioned in line with the first combustion chamber  68  and has similar construction. Preferably, the engine  36  is tilted so that the combustion chambers have a centerline C which is offset from a vertical axis V. As is well known in the art, this arrangement keeps the vertical profile of the engine small, such that the watercraft  10  has a low center of gravity. 
     The engine  36  includes means (e.g., an intake manifold  78 ) for providing an air and fuel mixture to each combustion chamber. The intake manifold  78  has a silencer  80  mounted on the input end. Preferably, air is drawn into the engine compartment  38  and then drawn into the silencer  80  and delivered to the combustion chambers via the intake manifold  78 . As illustrated in FIG. 2, fuel is delivered to a fuel injector  82  through a fuel rail  84 . It is contemplated that the fuel may be provided by indirect or direct fuel injection, as well as via carburation, as known in the art. 
     As shown in FIG. 2, a catalyst  88  is located in the center of an exhaust pipe  86 . The exhaust pipe  86  wraps around the front of the engine  36  and extends to the rear of the watercraft  10  where it connects to a water lock  90 . An exhaust outlet  92  is located below a water a level L 1  when the watercraft is in the stationary position. The exhaust outlet  92  is located above a water level L 2  when the watercraft is planing. 
     A suitable ignition system is provided for igniting the air and fuel mixture provided to each combustion chamber. Preferably, this system comprises a spark plug (not shown) corresponding to each combustion chamber. The spark plugs are preferably fired by a suitable ignition system. 
     It is contemplated that the ignition system incorporates preprogrammed ignition maps to control the ignition spark advance curve. In a similar way, both the indirect and direct fuel injection systems incorporate pre-programmed fuel delivery maps to control fuel injection timing issues. The ignition maps and the fuel delivery maps are software that are part of a control system. 
     As shown in FIG. 2, the control system includes an atmospheric pressure sensor  94 , which can be mounted in the engine compartment  38  or mounted directly on the engine  36 . As shown in FIG. 3, an inlet pressure sensor  96  is mounted at a ramp  98  at the forward side of the water inlet  58 . As further shown in FIG. 3, the inlet pressure sensor  96  can be replaced by a nozzle pressure sensor  99  mounted on the outlet  60 . The nozzle pressure sensor  99  detects nozzle pressure downstream of a set of stationary blades  100 . Furthermore both of the sensors  96  and  99  may be replaced with a watercraft speed sensor  102 . 
     The control system operates by a control routine as best seen in FIG.  4 . The program starts and then moves to a step P 1  to read the condition of the inlet pressure sensor  96  and determine if the inlet pressure is lower than the atmospheric pressure measured by the pressure sensor  94 . If the inlet pressure is lower, meaning water is traveling into the water inlet  58 , then the program moves to a step P 2  to allow the maximum engine rpm to be 7000. The program returns to the start of the control routine and repeats the reading and decision process as long as the engine is running. 
     If however, at the step P 1 , the inlet pressure measured by the sensor  96  is greater than or equal to the atmospheric pressure measured by the sensor  94 , the program moves to a step P 3 . In the step P 3  the program determines whether the inlet pressure measured by the sensor  96  has been greater than or equal to the atmospheric pressure for more than five seconds. If the measured inlet pressure has been greater than or equal to the atmospheric pressure for longer than five seconds, then the program moves to a step P 4  and limits the maximum engine rpm to 4000. The program returns to the start of the control routine and repeats the forgoing steps. 
     If, at the step P 3 , the measured inlet pressure has been greater than or equal to the atmospheric pressure for less than five seconds, then the program moves to the step P 2  to allow the maximum engine rpm to be 7000. The program returns to the start of the control routine and repeats the forgoing steps. The five-second delay period allows sufficient time for the control system to permit for short durations of out-of-water operation, caused for example, by porpoising or jumping, which commonly occurs with watercraft operation. The maximum engine speed is not reduced unless the watercraft remains out of the water for more than five seconds. 
     If the pressure sensor  96  is replaced with the nozzle pressure sensor  99 , the control sequence will determine in the step P 1  whether the nozzle pressure is higher than the atmospheric pressure measured by the sensor  94 . If the nozzle pressure is not higher than the atmospheric pressure, then in the step P 3 , the control sequence determines if the nozzle pressure was not higher than the atmospheric pressure for more than five seconds. Similarly, if a watercraft speed sensor is used instead of the pressure sensor  82 , then in step P 1 , the control sequence determines whether or not the watercraft speed is greater than a predetermined speed. If the watercraft speed is not greater than a predetermined speed, then in the step P 3 , the control sequence determines if the watercraft speed was less than the predetermined speed for more than 5 seconds before limiting the maximum engine speed. 
     In the preferred embodiment, the operational state of the watercraft can be advantageously determined using the pressure sensor  96 , the nozzle pressure sensor  99 , or the speed sensor, as long as the control sequence can determine if the watercraft is on the water or how long it is out of the water. 
     The inlet pressure sensor  96  can be advantageously located in different areas of the water passage as long as it is located in the general vicinity of the water inlet  58 . 
     If the control system regulates the engine speed using the ignition system, the firing of one or any of the cylinders may be completely or intermittently stopped, or the firing of all cylinders may be intermittently stopped. 
     Similarly, if the control system uses the fuel control to regulate engine speed, the fuel injection of one or any of the cylinders may be completely or intermittently stopped, or the fuel injection from all the cylinders may be intermittently stopped. 
     Thus, from the foregoing description, it should be readily apparent that the described embodiments very effectively control engine speed in order to reduce noise. Comparing the pressure measured in the water inlet to the atmospheric pressure in order to determine the operating condition of the watercraft accomplishes this. 
     Of course, the foregoing description is that of preferred embodiments of the invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.