Abstract:
A personal watercraft and engine therefor are provided. The engine typically is mounted in a personal watercraft and configured to discharge an exhaust gas through a water muffler. The engine typically includes a cylinder head forming a combustion chamber, wherein the cylinder head is provided with an exhaust port configured to draw the exhaust gas from the combustion chamber to the water muffler, and an air passage configured to allow the exhaust port and an outside of the engine to communicate with each other, and the air passage is provided with a valve configured to restrict a flow of air within the air passage.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an engine mounted in a personal watercraft and configured to discharge an exhaust gas through a water muffler, and the personal watercraft configured to drive a propulsion mechanism thereof by the engine.  
           [0003]    2. Description of the Related Art  
           [0004]    In recent years, jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. A typical personal watercraft includes an engine mounted in a space surrounded by a hull and a deck. The personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a bottom surface of the hull and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.  
           [0005]    The personal watercraft includes an exhaust system configured to discharge an exhaust gas from the engine outside the watercraft. Typically, the exhaust system includes a water muffler that serves to muffle a noise of the exhaust gas. The water muffler is provided at a location in a flow passage of the exhaust gas ranging from an exhaust port of the engine to an exhaust outlet provided in a body of the watercraft. In the case of the exhaust system including the water muffler, some cooling water is supplied to the exhaust gas from the engine and vaporized into a steam by heat of the exhaust gas. The energy of the exhaust gas containing the steam is reduced while the exhaust gas is flowing within the water muffler and the noise thereof is muffled.  
           [0006]    In general, an exit of the exhaust system leading outside the watercraft is provided under a waterline of the watercraft. The exhaust gas is discharged into water, thereby allowing the noise of the exhaust gas to be further reduced.  
           [0007]    When the watercraft finishes cruising and its engine is in a stopped state, some water droplets reside on an inner wall of the exhaust port through which a combustion chamber of the engine communicates with an outside of the engine. Possible causes of this problem are described below.  
           [0008]    First, the exhaust gas flowing within the exhaust port during an operation of the engine has a negative pressure intermittently due to pulsation of the exhaust gas, and under this negative-pressure condition, the exhaust gas containing the steam within the water muffler flows back toward the exhaust port.  
           [0009]    Second, the steam is filled in the exhaust system after the engine stops. Specifically, in the case of the watercraft in which a four-cycle engine is mounted, under the condition in which an exhaust valve is closed while the engine is in a stopped state, an inner space of the exhaust system ranging from the exhaust valve to the exhaust outlet submerged in water is closed. And, immediately after the engine stops, the water supplied to an inside of the exhaust system remains as the steam. The steam is filled within the exhaust system, and condenses on the inner wall of the exhaust port.  
           [0010]    Third, when the engine is in the stopped state, the steam within the exhaust system flows back toward an exhaust passage due to movement of a piston within a cylinder. Specifically, in the case of the four-cycle engine, when the engine stops while any of the cylinders is under a condition of compression stroke, a compressed gas within the combustion chamber sometimes causes the piston to be slightly pushed back toward a bottom dead center. Therefore, when the engine stops with the exhaust valve opened, and the piston moves toward the bottom dead center as described above, the steam remaining within the exhaust system flows back toward the exhaust port.  
           [0011]    Due to one or a plurality of the above described causes, the steam might condense on the inner wall of the exhaust passage. Undesirably, the water droplets on the inner wall of the exhaust port might cause rust. In particular, it is undesirable that the steam condenses on a portion of the exhaust port which is near the combustion chamber, whose temperature tends to become relatively high, and on the exhaust valve.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention addresses the above described conditions, and an object of the present invention is to provide an engine capable of inhibiting a steam in an exhaust gas from condensing on an inner wall of an exhaust port of the engine, and a personal watercraft configured to drive a propulsion mechanism of the watercraft by the engine.  
           [0013]    According to one aspect of the present invention, there is provided an engine mounted in a watercraft and configured to discharge an exhaust gas through a water muffler, comprising a cylinder head forming a combustion chamber, wherein the cylinder head is provided with an exhaust port configured to draw the exhaust gas from the combustion chamber to the water muffler, and an air passage configured to allow the exhaust port and an outside of the engine to communicate with each other, and the air passage is provided with a valve configured to restrict a flow of air flowing within the air passage.  
           [0014]    With the above construction, since ambient air is introduced into the exhaust port of the cylinder head through the air passage, it is possible to inhibit the steam generated within the exhaust system including the water muffler located downstream in a flow passage of the exhaust gas from flowing back toward the exhaust port. As a result, it is possible to inhibit the steam from condensing to form droplets on the inner wall of the exhaust port.  
           [0015]    The valve may be configured to permit the flow of air from the outside of the engine toward the exhaust port when a pressure within the exhaust port is lower than a pressure outside the engine, and may be configured not to permit the flow of the air from the exhaust port toward the outside of the engine when the pressure within the exhaust port is higher than the pressure of the outside of the engine. In such a configuration, when the exhaust port has a negative pressure due to pulsation of the exhaust gas, or due to movement of the piston after the engine stops, the ambient air is introduced into the exhaust port. Thereby, the steam generated within the exhaust system can be inhibited from flowing back toward the exhaust port.  
           [0016]    The valve may be configured to permit the flow of the air within the air passage when the engine is in a stopping or stopped state. For example, the engine may further comprise a sensor configured to detect an engine speed of the engine, wherein the valve may be an electromagnetic valve configured to be driven based on a detection signal from the sensor. Based on the detection signal from the sensor, it can be judged whether or not the engine is in the stopping or stopped state. Then, based on this judgment, the electromagnetic valve can be opened after the engine stops. Since the ambient air is introduced into the exhaust port through the air passage or the steam remaining within the exhaust system can be discharged through the air passage after the engine stops, the steam is inhibited from condensing to form droplets on the inner wall of the exhaust port. As the sensor, a crank position sensor configured to detect the number of rotations of a crankshaft may be used.  
           [0017]    The air passage may be configured to be connected to the exhaust port in the vicinity of an end of the exhaust port on the combustion chamber side. In such a configuration, the steam is inhibited from condensing to form droplets on a portion of the exhaust port in the vicinity of the combustion chamber or on the exhaust valve. Also, while the engine is operating, the negative pressure tends to be generated due to pulsation of the exhaust gas at a location of the exhaust port which is closer to the combustion chamber. So, by connecting the air passage to this location of the exhaust port, the ambient air is reliably introduced utilizing the negative pressure.  
           [0018]    The cylinder head, the exhaust port, and the air passage may be associated with one of a plurality of cylinders of the engine; the air passage may be divided into a plurality of sub-passages; each of the plurality of cylinders may include the exhaust port; and the air passage may be configured to fluidically connect each exhaust port to the outside of the engine, through the corresponding sub-passage. In such a construction, the steam is inhibited from condensing to form droplets on the inner wall of the exhaust port of each cylinder.  
           [0019]    The sub-passages may be merged at a location thereof into a merged portion of the air passage, and the valve may be provided so as to be closer to the outside of the engine than to the location where the sub-passages are merged. In such a construction, it is not necessary to provide the valve in each of the sub-passages. By merging all the sub-passages, one valve is sufficient. This leads to a reduced cost.  
           [0020]    According to another aspect of the present invention, there is provided a personal watercraft comprising an engine mounted within a body of the watercraft, and a water muffler equipped within the body and configured to be connected to the engine to allow an exhaust gas from the engine to flow within the water muffler, wherein the engine includes a cylinder head forming a combustion chamber, the cylinder head is provided with an exhaust port configured to draw an exhaust gas from the combustion chamber to an outside of the cylinder head, and an air passage configured to allow the exhaust port and the outside of the engine to communicate with each other, and the air passage is provided with a valve configured to restrict a flow of air within the air passage.  
           [0021]    With the above construction, the personal watercraft equipped with the exhaust system including the water muffler can have the engine capable of inhibiting the steam in the exhaust gas from condensing to form droplets on the inner wall of the exhaust port.  
           [0022]    The personal watercraft may further comprise a sensor configured to detect an engine speed of the engine, and a control device configured to receive a detection signal from the sensor and configured to, based on the received signal, transmit a signal indicative of whether or not the engine is in the stopping or stopped state, to the valve, wherein the valve may be an electromagnetic valve configured to be driven based on the signal from the control device. In this case, a crank position sensor may be used to detect an engine speed of the engine, and based on the detection result, the control device judges whether or not the engine is in the stopping or stopped state. When judging that the engine is in the stopping or stopped state, the control device transmits a predetermined signal to the electromagnetic valve to cause the electromagnetic valve to open. Thereby, after the engine stops, the air passage opens, so that the steam is inhibited from condensing to form droplets on the inner wall of the exhaust port.  
           [0023]    The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    [0024]FIG. 1 is a side view of a personal watercraft according to an embodiment of the present invention;  
         [0025]    [0025]FIG. 2 is a plan view of the personal watercraft in FIG. 1;  
         [0026]    [0026]FIG. 3 is a plan view showing a construction of an engine and an exhaust system mounted in the personal watercraft in FIG. 1;  
         [0027]    [0027]FIG. 4 is a cross-sectional view of the engine in FIG. 3, taken along line IV-IV;  
         [0028]    [0028]FIG. 5 is a cross-sectional view showing another construction of the engine mounted in the personal watercraft in FIG. 1; and  
         [0029]    [0029]FIG. 6 is a side view showing another construction of the engine mounted in the personal watercraft in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    Hereinafter, embodiments of a personal watercraft of the present invention will be described with reference to the accompanying drawings. The personal watercraft in FIG. 1 is a straddle-type personal watercraft provided with a seat  7  straddled by a rider. A body  1  of the watercraft comprises a hull  2  and a deck  3  covering the hull  2  from above. A line at which the hull  2  and the deck  3  are connected over the entire perimeter thereof is called a gunnel line  4 . A waterline  5  of the watercraft is located below the gunnel line  4  when the watercraft is at rest on water.  
         [0031]    As shown in FIG. 2, an opening  6 , which has a substantially rectangular shape as seen from above, is formed at a substantially center section of the deck  3  in the upper portion of the body  1  such that its longitudinal direction corresponds with the longitudinal direction of the body  1 . The seat  7  is removably mounted over the opening  6 .  
         [0032]    An engine room  8  is provided in a space defined by the hull  2  and the deck  3  below the opening  6 . An engine E is mounted within the engine room  8  and configured to drive the watercraft. The engine room  8  has a convex-shaped transverse cross-section and is configured such that its upper portion is smaller than its lower portion. In this embodiment, the engine E is an in-line four-cylinder four-cycle engine. As shown in FIG. 1, the engine E is mounted such that a crankshaft  9  extends along the longitudinal direction of the body  1 .  
         [0033]    An output end of the crankshaft  9  is rotatably coupled integrally with a pump shaft  11  of a water jet pump P provided on the rear side of the body  1  through a propeller shaft  10 . An impeller  12  is attached on the pump shaft  11  of the water jet pump P. Fairing vanes  13  are provided behind the impeller  12 . The impeller  12  is covered with a pump casing  14  on the outer periphery thereof.  
         [0034]    A water intake  15  is provided on the bottom of the body  1 . The water intake  15  is connected to the pump casing  14  through a water passage. The pump casing  14  is connected to a pump nozzle  16  provided on the rear side of the body  1 . The pump nozzle  16  has a cross-sectional area that gradually reduces rearward, and an outlet port  17  is provided on the rear end of the pump nozzle  16 .  
         [0035]    The water outside the watercraft is sucked from the water intake  15  and fed to the water jet pump P. The water jet pump P pressurizes and accelerates the water and the fairing vanes  13  guide water flow behind the impeller  12 . The water is ejected through the pump nozzle  16  and from the outlet port  17  and, as the resulting reaction, the watercraft obtains a propulsion force.  
         [0036]    The engine E according to this embodiment uses an open-looped cooling system. As shown in FIG. 1, a water-drawing hole  18  is provided at a predetermined location in an upper portion of the pump casing  14 . Some of the water being pressurized by the water jet pump P is drawn into the watercraft for use as cooling water through the water-drawing hole  18  and supplied to a cooling system equipped in the watercraft to cool the engine E or the like.  
         [0037]    A bar-type steering handle  20  is provided at a front portion of the deck  3 . The steering handle  20  is connected to a steering nozzle  21  provided behind the pump nozzle  16  through a cable  22  in FIG. 2. When the rider rotates the handle  20  clockwise or counterclockwise, the steering nozzle  21  is swung toward the opposite direction so that the ejection direction of the water being ejected through the pump nozzle  16  can be changed, and the watercraft can be correspondingly turned to any desired direction while the water jet pump P is generating the propulsion force.  
         [0038]    As shown in FIG. 1, a bowl-shaped reverse deflector  23  is provided on the rear side of the body  1  and on the upper side of the steering nozzle  21 . The deflector  23  is supported by a horizontally provided swinging shaft  24  of the watercraft such that it can vertically swing around the swinging shaft  24 . The deflector  23  is swung downward to a lower position around the swinging shaft  24  to deflect the ejected water from the steering nozzle  21  forward and, as the resulting reaction, the personal watercraft moves rearward.  
         [0039]    As shown in FIG. 3, in a construction of the engine E and an exhaust system  100  of the personal watercraft, the engine E is placed forward of the pump casing  14 . An end portion of each of a plurality of passages of air-intake manifold  32  is connected to a corresponding one of a plurality of air-intake inlet (entrance of the air-intake ports  60  mentioned later: see FIG. 4)  31  provided on the right side of a cylinder head  30  of the engine E, and each of a plurality of end portions of passages of exhaust manifold  34  is connected to a corresponding one of a plurality of exhaust outlets (exits of exhaust ports  61  mentioned later: see FIG. 4)  33  provided on the left side of the cylinder head  30 .  
         [0040]    An upstream muffler  40  is provided on the left side of the pump casing  14 . The exhaust manifold  34  is connected to the upstream muffler  40  through a first exhaust pipe  35 , a rubber pipe  36 , and a second exhaust pipe  37  in successive order. A downstream muffler  41  is provided on the right side of the pump casing  14  so as to be located rearward with respect to the upstream muffler  40 . The upstream muffler  40  and the downstream muffler  41  communicate with each other through a first connecting pipe  42  provided over the pump casing  14 . One end portion of a second connecting pipe  43  is connected to the downstream muffler  41  and the other end portion thereof penetrates the hull  2  and forms an exhaust outlet  45  of the exhaust system  100 . The exhaust outlet  45  is located under the waterline  5  of the watercraft (see FIG. 1). Thus, the exhaust system  100  forms a flow passage of an exhaust gas ranging from the exhaust manifold  34  to the exhaust outlet  45 .  
         [0041]    The first exhaust pipe  35  has a double-walled structure provided with a water jacket (not shown) within which the cooling water flows. A water-supply hole  46  is provided on a wall portion of the second exhaust pipe  37  to allow some of the cooling water being drawn through the water-drawing hole  18  to be supplied to the second exhaust pipe  37 . The water supplied from the water-supply hole  46  to the second exhaust pipe  37  makes contact with a high-temperature exhaust gas being discharged from the engine E, and thereby is vaporized into a steam, which flows within the upstream muffler  40  and the downstream muffler  41 . The upstream muffler  40  and the downstream muffler  41  are water mufflers, where the energy of the exhaust gas is reduced and thereby the noise of the exhaust gas is reduced.  
       Embodiment 1  
       [0042]    As shown in FIG. 4, which is a cross-sectional view of the engine E in FIG. 3, taken along line IV-IV, the engine E (E 1 ) is configured such that an upper portion of the cylinder head  30  is covered with a cylinder head cover  50  from above, and a cylinder block  51  and a crankcase  52  are provided in successive order below the cylinder head  50 . A piston  53  is provided within the cylinder block  51  and configured to reciprocate. A space defined by an upper end face of the piston  53 , the cylinder block  51 , and the cylinder head  30  form a combustion chamber  54 .  
         [0043]    The air-intake ports  60  and the exhaust ports  61  are formed in the cylinder head  30 . The air-intake ports  60  are configured to allow an outside of the cylinder head  30  to communicate with the combustion chamber  54  and the exhaust ports  61  are configured to allow the outside of the cylinder head  30  to communicate with the combustion chamber  54 . The air-intake ports  60  and the exhaust ports  61  are provided so as to correspond to four cylinders included in the engine E 1 . In such a construction, air drawn into the combustion chamber  54  through an air-intake system including the air-intake manifold  32  and the air-intake ports  60  is combusted therein and, thereafter, is discharged outside the watercraft through the exhaust system  100  (see FIG. 3) including the exhaust ports  61 , the upstream muffler  40 , and the downstream muffler  41 .  
         [0044]    A space defined by the cylinder head  30  and the cylinder head cover  50  form a cam chamber  62 . Exhaust valves  63  are each provided between the cam chamber  62  and a vicinity of an upstream end of the corresponding exhaust port  61  so as to penetrate the cylinder head  30 . The exhaust valves  63  are each comprised of a stick-shaped valve stem  64  and a valve portion (mushroom)  65  provided at a lower end of the valve stem  64 . The valve portion  65  is located at an upstream opening end of the exhaust port  61 . The exhaust valve  63  is operated in cooperation with rotation of the crankshaft  9  (see FIG. 1), thereby causing the upstream opening of the exhaust port  61  to open and close.  
         [0045]    The cylinder head  30  and the cylinder head cover  50  are provided with air passages  70  configured to penetrate the head  30  and the cover  50 . One end of each of the air passages  70  are each connected to a vicinity of an end of the corresponding exhaust port  61  on the combustion chamber  54  side, and are each configured to open toward an inside of the corresponding exhaust port  61 . The other ends of each of the air passages  70  extend through an upper portion of the cylinder head cover  50  and are configured to open outside the engine E 1 . Therefore, the air passages  70  are each configured to fluidically connect the corresponding exhaust port  61  to the outside of the engine E. One-way valves  71  are each provided at a location of the corresponding air passage  70  to regulate a flow of the air within the corresponding air passage  70 . The one-way valves  71  are each mechanically driven to open and close based on a pressure difference between one end portion and the other end portion of the corresponding air passage  70  in such a manner that, when a pressure within the exhaust port  61  is lower than a pressure outside the engine E 1 , the valve  71  opens while, when the pressure within the exhaust port  61  is higher than the pressure of outside the engine E 1 , the valve  71  closes. That is, the one-way valve  71  permits only the flow of the air from the outside the engine E 1  to the exhaust port  61 . The air passage  70  and the one-way valve  71  are provided in the same configuration in each of the exhaust ports  61 , provided respectively so as to correspond to the four cylinders included in the engine E 1 .  
         [0046]    An operation of the engine E 1  constructed as described above will be described. While the engine E 1  is operating, the exhaust valve  63  operates, thereby causing the upstream opening of the exhaust port  61  to open and close, so that density of the exhaust gas (or exhaust pressure) varies with a lapse of time. When the exhaust pressure within the exhaust port  61  is lower, ambient air is introduced into the exhaust port  61  through the air passage  70  and the one-way valve  71 . As a result, it is possible to inhibit the exhaust gas containing the steam from flowing back from a downstream side of the exhaust system  100  toward the exhaust port  61 .  
         [0047]    When the engine E 1  stops with the exhaust valve  63  opening in any one of the four cylinders, and the piston  53  moves toward the bottom dead center (see an arrow  72  in FIG. 4), the pressure within the exhaust port  61  becomes lower. Under this condition, also, the ambient air is introduced into the exhaust port  61  through the air passage  70 . Therefore, when the pressure within the exhaust port  61  becomes lower with downward movement of the piston  53 , it is possible to inhibit the steam from flowing from the downstream side of the exhaust system  100  toward the exhaust port  61 .  
       Embodiment 2  
       [0048]    The engine E having another construction will be described with reference to FIG. 5. An engine E (E 2 ) in FIG. 5 is provided with an electromagnetic valve  73  configured to be driven to open and close in accordance with an electric signal externally input, instead of the one-way valve  71  included in the engine E 1  in FIG. 4. A crank position sensor (hereinafter “CPS”)  74  is provided in a crankcase  52  of the engine E 2  to detect a rotational angle of the crankshaft  9 . The engine E 2  is mounted in the personal watercraft. An electric control unit (ECU)  75  is equipped in the personal watercraft and configured to control drive of the engine E 2 . And, the electromagnetic valve  73  and the CPS  74  are each electrically connected to the ECU  75 .  
         [0049]    An operation of the engine E 2  constructed as described above will be described. While a signal from the ECU  75  is not input to the electromagnetic valve  73 , the electromagnetic valve  73  maintains its closed state. The CPS  74  regularly detects the rotational angle of the crankshaft  9  and transmits the resulting signal to the ECU  75 . Upon reception of the signal from the CPS  74 , the ECU  75  judges an operating state of the engine E 2  based on the received signal.  
         [0050]    When judging that the engine E 2  is in a stopping or stopped state, the ECU  75  outputs a signal indicative of this to the electromagnetic valve  73 . Upon reception of the signal from the ECU 75 , the electromagnetic valve  73  opens. Thereby, the outside of the engine E 2  communicates with the exhaust port  61  through the air passage  70 , thereby allowing a gas to flow between the outside of the engine E 2  and the exhaust port  61 .  
         [0051]    In the engine E 2  constructed as described above, when the engine E 2  stops and the exhaust port  61  has a negative pressure, ambient air is introduced through the air passage  70 . Under this condition, the steam within the exhaust system  100  does not flow back toward the exhaust port  61 . Also, even when the exhaust system  100  is closed and the steam is filled within the exhaust system  100 , the exhaust port  61  communicates with the outside of the engine E 2  through the air passage  70  as soon as the engine E 2  stops, thereby allowing the steam filled within the exhaust system  100  to be discharged outside through the air passage  70 .  
         [0052]    In the construction of the engine E 2  in FIG. 5, the same reference numerals as those in the engine E 1  in FIG. 4 denote the same or corresponding parts, which will not be described in detail. The signal from the CPS  74  is used to judge whether or not the engine E 2  is in a stopping or stopped state, but this is only illustrative. Alternatively, this judgment may be made, based on whether or not an ignition plug of the engine E 2  has been ignited. As another alternative, the ECU  75  may be replaced by a driver configured to drive the electromagnetic valve  73  based on the signal from the CPS  74 .  
       Embodiment 3  
       [0053]    Another construction of the engine E will be described with reference to FIG. 6. An engine E 3  in FIG. 6 is provided with air passages (sub-passages)  80  as corresponding to the cylinders. As in the air passages  70  in FIGS. 4 and 5, one end of each of the air passages  80  are connected to the exhaust ports  61  and the other end thereof is placed outside of the engine E 3 .  
         [0054]    The engine E 3  in FIG. 6 differs from the engine E 1  in FIG. 4 in that the air passages  80  are merged at a location  81  to be formed into one air passage  82 . A one-way valve  83  is provided in the air passage  82  so as to be closer to the other end of the air passage  82  (or outside of the engine E 3 ) than to the location  81 .  
         [0055]    The other construction of the engine E 3  in FIG. 6 is similar to that of the engine E 1  in FIG. 4 except the air passages  80  and  82  and the one-way valve  83 , and will not be further described.  
         [0056]    In the engine E 3  constructed above, it is not necessary to provide one-way valves so as to respectively correspond to the air passages  80 . The valve (lead valve)  83  produces similar effects provided by the construction of the first embodiment and, therefore, the engine E 3  is manufactured at a low cost.  
         [0057]    The one-way valve  83  may be replaced by an electromagnetic valve. Also, other valves may be used. The electromagnetic valve may be configured to open and close based on the signal from the ECU as described in the second embodiment. In this configuration, the valve is driven to open and close properly according to an operational state of the engine E; for example, while the engine E is a stopped state.  
         [0058]    While the engine E 3  is constructed such that all the air passages  80  corresponding to the four cylinders are merged, the air passages  80  corresponding to two or three cylinders may be merged.  
         [0059]    As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the above embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.