Patent Publication Number: US-6220907-B1

Title: Watercraft exhaust control

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a small watercraft such as a personal watercraft and more particularly to an improved exhaust system therefore. 
     There is a very popular class of watercraft referred to as “personal watercraft.” The watercraft that fall into this class are of a wide variety of types but have in common the feature that they are designed to be operated primarily by a single rider operator and which may carry no more than three additional passengers. Frequently, the operator sits in a straddle fashion and if passengers are accommodated they sit in tandem with the operator. This is not necessarily true in all cases but it does indicate the compact nature of this type of watercraft. 
     This type of watercraft is also quite sporting in nature. Because of these factors, conventional boaters have some objections to this type of watercraft. 
     One feature which is objected to by some people with this type of watercraft is the noise which they generate. The engine exhaust is generally silenced by utilizing a plurality of expansion chambers that are disposed between the exhaust ports and the point of discharge of the exhaust gases to the atmosphere. Because of the small space available, more sophisticated exhaust systems like utilize an automotive or larger power boat applications are not possible. 
     Also, it is the conventional practice with many types of water propulsion systems to silence the engine exhaust noises by cooling the exhaust gases either through water jacketing the exhaust system or by dumping cooling water from the engine cooling jacket into the exhaust system. Frequently, both of these expedients are combined. 
     These types of systems are effective for some sound frequencies, but not all of those experienced with engines, particularly of the two cycle type. Because of the fact that there may be a high quantity of water in the exhaust, this makes the use of other types of exhaust silencers difficult. 
     It is, therefore, a principal object of this invention to provide an improved silencing system for a personal watercraft. 
     Many of the silencing devices employed for silencing exhaust sounds at certain frequencies or certain running conditions provide restriction in the air flow and can reduce maximum power output. 
     It is, therefore, a further object of this invention to provide an improved exhaust silencing device that can be utilized to provide silencing under some running conditions and which silencing is accomplished by restricting the exhaust flow but which, under other running conditions, does not provide this effect. 
     SUMMARY OF THE INVENTION 
     This invention is adapted to be embodied in a personal watercraft having a hull that defines a rider&#39;s area for accommodating a rider operator and not more than three additional passengers. An engine compartment is provided within the hull and contains a powering internal combustion engine. This engine drives a propulsion device for propelling the watercraft through the body of water in which it is operated. The engine is provided with an exhaust system by which exhaust gases are discharged to the atmosphere. This exhaust system includes at least one expansion chamber device that receives the exhaust gases from the engine and which eventually transmits them to the atmosphere. A conduit extends from this water trap device to an atmospheric discharge. A silencer valve is disposed in this conduit for silencing sounds in the exhaust by restricting the flow therethrough only under certain running conditions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a personal watercraft constructed in accordance with an embodiment of the invention, with a portion of the hull broken away so as to show the engine, propulsion unit and exhaust system. 
     FIG. 2 is a top plan view of the watercraft shown in FIG. 1 with the hull being shown only in outline and the engine and propulsion system and exhaust being shown in solid lines. 
     FIG. 3 is an enlarged cross-sectional view showing the silencing device and its orientation in the hull. 
     FIG. 4 is a graphical view showing exhaust silencing valve position in relation to engine or vessel speed to explain the control strategy. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
     Referring first to FIGS. 1-3, a personal watercraft constructed in accordance with a preferred embodiment is identified generally by the reference numeral  11 . When the term “personal watercraft” is utilized, it is intended to encompass the type of watercraft defined in the preamble of this application as such watercraft. 
     The watercraft  1   1  is comprised of a hull assembly that is comprised of a hull  12  and a deck portion  13  which is affixed thereto. The hull  12  and deck portion  13  are formed from a suitable material such as a molded fiberglass reinforced resin or the like. The components are affixed together in a suitable manner and define an engine compartment  14 . 
     The deck portion  13  has provided at its forward part a control mast  15  for control of the watercraft  11 . A longitudinally extending seat  16  is formed behind this mast  15 . The seat  16  is designed so as to accommodate a single rider operator positioned immediately behind the mast  15 . Additional passengers may be carried behind the operator and they will be seated in tandem fashion. No more than three passengers normally occupy this seat  16  along with the rider operator. It should be understood that the foregoing seating arrangement is only typical of the type with which the invention may be employed. 
     An internal combustion engine, indicated generally by the reference numeral  17  is provided in the engine compartment  14  and is disposed beneath the seat  16 . Therefore, the deck portion  13  may be formed with an access opening that can be accessed through removal of the seat  16  or a part thereof it. 
     The engine  17  is, in the illustrated embodiment, mounted so that its crankshaft rotates about a longitudinally extending axis L. This facilitates coupling to a driveshaft  18  which extends rearwardly and is coupled to the impeller shaft of a jet propulsion unit, indicated generally by the reference numeral  19 . 
     This jet propulsion unit  19  includes an outer housing assembly  21  that forms a downwardly facing water inlet opening  22  through which water may be drawn from the body of water in which the watercraft  11  is operating. This water is pumped by an impeller shown schematically at  23  in FIG.  1  and is discharged rearwardly through a discharge nozzle  24  to provide a propulsion force for the watercraft  11 . 
     As is also known in this art, a steering nozzle  25  is pivotally supported in communication with the discharge nozzle  24 . The pivotal position of the steering nozzle  25  is controlled by the mast  15  for steering of the watercraft  11  in a manner well known in this art. 
     It should be noted that the jet propulsion unit  19  may be accommodated in part in a tunnel formed at the rearward end of the hull portion  12 . A suitable bulkhead assembly isolates the engine compartment  14  from this tunnel. 
     The construction of the watercraft  11  as thus far described may be considered to be conventional. As has been noted above, the invention deals primarily with the exhaust system for the engine  17  and that will now be described referring initially primarily to FIGS. 1 and 2. 
     The engine  17  may be of any known type. However, in the illustrated embodiment it is depicted as being the two cylinder inline type that operates on a crankcase compression principal. The invention has particularly utility with this type of engine because such engines frequently generate noises that may be objectionable. Of course, the invention can be utilized with engines of other types and other cylinder numbers and configurations. 
     A combined expansion chamber, exhaust manifold  26  has an inlet end that is fixed to a side of the cylinder block of the engine  17  and collects the exhaust gases from the exhaust port. These exhaust gases are silenced by this expansion and then are again compressed and transferred rearwardly to a water trap device  27  that is disposed on one side of the jet propulsion unit  21  and externally of the hull tunnel portion in which part of this jet propulsion unit may be contained. 
     The water trap device  27 , as is typical in the art, has an inlet  28  at one end thereof from which the exhaust gases from the exhaust manifold  26  are delivered to an upper area of the expansion chamber formed by the water trap device  27 . An exhaust discharge pipe  29  extends from a lower portion of the outer housing of the water trap device  27  vertically upwardly and crosses over the top of the jet propulsion unit  19  and the tunnel in which it is contained. This helps to assist in water separation and to ensure that water is not likely to flow backward to the engine through the exhaust system. 
     Normally, the pipe  29  would discharge the exhaust gases to the atmosphere. In accordance with the invention, however, a silencing device  31  is provided in this exhaust pipe  29  and has a construction as best shown in FIG.  3 . The exhaust silencing device  31  is comprised of a exhaust control valve assembly which restricts the flow area of the exhaust pipe  29  under certain running conditions to provide exhaust silencing and improved performance while providing substantially no significant restrictions under other running conditions. 
     This device and its operation may be thus understood by reference to FIG.  3 . As shown in FIG. 3, the silencing device  31  includes a tubular section  30  formed at the end of the exhaust pipe  29  and which terminates in a discharge pipe  32  that extends through a portion of the hull  12  and which has a downwardly and rearwardly facing discharge opening  33 . 
     A control valve assembly, indicated generally by the reference numeral  34  is provided in the pipe section  30 . This control valve assembly  34  includes a plate-type valve  35  that is rotatably journaled in a passage  30 a of the pipe section  30  on a control valve shaft  36 . This shaft  36  extends transversely across the flow passage  30   a.    
     FIG. 3 shows in solid lines the closed position of the valve plate  35 . Actually, this figure is somewhat of an exaggeration because in this position, the valve plate  35  does not completely close the flow passage  31 . That is, there is a clearance between the outer periphery of the control valve  35  and the inner periphery of the pipe section  30  that will provide adequate air flow for engine running conditions up to a predetermined speed and load. Nevertheless, the restriction is adequate to provide a good silencing effect. 
     One end of the shaft  36  extends outwardly beyond the tubular member  30 . A pulley  37  is affixed to this extending end and a belt  38  is trained around the pulley  37 . A servo motor  39  is mounted at a convenient location and has an output shaft  41  to which a driving pulley  42  is affixed. This driving pulley  42  drives the belt  38  and, accordingly, moves the control valve plate  35  between its closed position as shown in solid lines in FIG.  3  and its open non-restricting position as shown in phantom line in this same figure. 
     An ECU  43  is provided in the watercraft and receives signals indicative of engine speed and/or load so as to adjust the position of the control valve element  35  in accordance with a control routine as best shown in FIG.  4 . 
     As seen in this figure, the control valve opening defined as a percentage of total effective flow area between closed and fully opened is varied in response to engine speed. This is done so that in normal non-planing watercraft condition, the control valve element  35  is maintained in its closed position. However, upon reaching the transition stage before planing, the control valve is rapidly opened so as to reduce the flow restriction, increase power and facilitate acceleration to a planing condition. This opening is done during the transition stage and it may begin either at the beginning of the transition stage as shown in solid lines or slightly before that as shown in phantom line. In any event, the control valve  35  is fully opened before planing condition is totally reached. 
     Thus, it should be apparent from the foregoing description that the use of the control valve arrangement as described provides this silencing when operating under lower speeds and before planing. However, the control valve is opened during the transitional stage to planing operation so as to permit good power output to be obtained and when the loss of silencing will not be significant. Of course, the foregoing description is that of the preferred embodiment 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.