Abstract:
A jet propelled watercraft having an improved extension assembly for dampening pulsations from the impeller of the jet propulsion unit and also for mounting the jet propulsion unit. The structure simplifies the overall assembly and permits individual tuning with conventional units.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation in part of the application of the same title, U.S. Ser. No. 09/630,668, filed Aug. 2, 2000 and assigned to the assignee hereof. 
    
    
     BACKGROUND OF INVENTION 
     This invention relates to a jet propulsion system for a watercraft and more particularly to an improved device for minimizing the sounds and vibrations generated by the jet propulsion unit. 
     Jet propulsion units are quite popular in connection with the propulsion of watercraft and especially a particular type of watercraft referred to as a “personal watercraft”. These types of watercraft generally are designed to be operated by a rider who may carry no more than one to three additional passengers. Frequently these passengers are seated in straddle, tandem fashion on a longitudinally extending seat that is formed at the rear of the watercraft with the propulsion unit being disposed beneath the seat. 
     One problem particular with this type of construction can be best understood by reference to the aforenoted copending application. As noted therein in conventional constructions the water inlet passage through the lower part of the watercraft hull curve upwardly from their inlet opening and directly registered with the impeller housing of the jet pump in close proximity to its impeller. It has been found that this causes pulsations in the water that is transmitted back through the forward wall of the bulkhead that separates the jet pump from the engine compartment and can create unpleasant vibrations in the watercraft and sounds that are undesirable. 
     It is, therefore, a first principal feature of this invention to provide an improved and low cost jet propulsion unit for a personal watercraft that avoids these pulsations. 
     It is a further object of this invention to provide an arrangement for utilizing this feature in conjunction with conventional type jet pumps so as to not require a redesign in either the hull or the jet pump in order to use the feature of the invention. 
     The copending application presents a solution to this problem, but further improvements are desirable. It is therefore another object of this invention to provide such further improvements. 
     SUMMARY OF INVENTION 
     This invention is adapted to be embodied in a personal watercraft that is comprised of a hull having an undersurface including a vertically extending bulkhead defining in part a rear portion of an engine compartment containing a prime mover. The hull undersurface defines at least in part a downwardly facing water inlet opening through which water may be drawn and a curved discharged path that curves upwardly from said water inlet opening toward the bulkhead. A support plate is fixed to the rear side of the bulkhead. An extension housing is affixed to the support plate at one end thereof. A jet propulsion system is carried by the other end of the extension housing. The jet propulsion system is comprised of an outer housing having an impeller portion, an impeller rotatably journalled about an impeller axis in the impeller portion and driven by the prime mover and a discharge nozzle portion positioned rearwardly of the impeller though which the water pumped by the impeller is discharged for propelling the personal watercraft. The support plate and the extension housing defining a water opening path leading in a direction parallel to the impeller axis and having a shape that constitutes generally an extension of the opening of an inlet to the impeller housing portion so as to isolate the pulsations generated by the impeller. The water opening path has a length greater than the axial length of the impeller. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a side elevational view of a personal watercraft constructed in accordance with an embodiment of the invention. 
     FIG. 2 is an enlarged broken away view showing the construction of the jet pump arrangement of embodiment shown in FIG.  1 . 
     FIG. 3 is an enlarged front elevational view showing the front or inlet face of the support plate for the jet propulsion unit in accordance with this embodiment of the invention. 
     FIG. 4 is a cross sectional view taken along the line  4 — 4  of FIG.  3  and shows the attached components. 
     FIG. 5 is a bottom plan view of the components shown in FIG.  2  and which comprise generally the underlying units of the jet propulsion system. 
     FIG. 6 is a cross sectional view in part similar to FIG. 2, but showing a further embodiment of the invention. 
     FIG. 7 is a further enlarged cross sectional view of a portion of the structure shown in FIG.  6 . 
    
    
     DETAILED DESCRIPTION 
     Referring in detail first to FIG. 1, a personal watercraft constructed in accordance with an embodiment of the invention is shown and identified generally by the reference numeral  11 . It is to be understood that, although the invention is described in conjunction with a personal watercraft, certain of the features herein disclosed may be utilized with other types of watercraft. However, the invention has particular utility in conjunction with personal watercraft due to their small size, compact nature and due to the increased demand for providing quieter operating watercraft of this type. 
     The watercraft  11  is comprised of a hull that consists primarily of a hull under portion  12  and deck portion  13  that are connected to each other along their peripheral edges by a gunnel  14 . The deck portion  13  has longitudinally extending riders, area on which a straddle type seat  15  on which the rider/operator and two or three additional passengers may be seated. The seating is in straddle, tandem position and the operator and his passengers place their feet in foot wells disposed on opposites sides of the seat  15 . 
     A control handlebar  16  is positioned forwardly of the seat  15  for operation by the rider/operator so as to steer the watercraft, control it speed and other functions. 
     A prime mover such as an internal combustion engine, shown schematically at  17  is contained in an engine compartment that is formed within the hull under portion  12  and which may be accessible through removal of the seat  15  and exposure of an access opening formed in the raised part of the riders&#39; area of the deck portion  13 . This engine  17  drives a jet propulsion unit, indicated generally by the reference numeral  18 , positioned in a tunnel at the rear of the hull under portion  12  in a manner, which will be described now in connection with reference to FIGS. 1 through 5. 
     Referring now primarily to these figures, the hull under portion  12  has a portion that defines a tunnel  19  in which the conventional jet propulsion unit housing assembly is mounted. This conventional part of unit includes the impeller housing portion  21  that contains the impeller  22 , a discharge nozzle portion  23 , a steering nozzle  24  and a reverse thrust bucket  25 . In FIG. 2, the reverse thrust bucket  25  is shown in its opened or forward drive condition. 
     In this embodiment, the impeller housing portion  21  is disposed rearwardly from a bulkhead  26  formed by the hull under portion  12  forwardly of the tunnel  19  and at the rear of the compartment containing the engine  17  so as to accommodate a silencing or extension and mounting assembly, indicated generally by the reference numeral  27 . This silencing extension assembly  27  will be described in more detail later by reference to FIGS. 2-5. It is this silencing extension assembly  27  that is utilized, at least in part, to secure the jet propulsion unit impeller housing portion  21  and other attached components to the bulkhead  26 . 
     In this assembly, a ride plate, indicated generally by the reference numeral  28  and as seen in FIG. 5, is comprised of flanges that receive threaded fasteners  29  for affixing it suitably to the hull under portion  12 . 
     It will be seen from FIG. 2 that forwardly of the bulkhead  26  the hull under portion  12  has a generally curved configuration  31  that defines a water inlet passage  32  that curves upwardly and which registers with the silencing extension assembly  27  in manner to be described. However, the generally curved configuration  31  is formed with an indentation  33  which cooperates with a grill assembly  34  that has a plurality of spaced grilled bars and mounting portion  35  at its forward end. Threaded fasteners  36  connect this portion of the grill assembly  34  to a reinforcement plate formed on the inner surface of the hull generally curved configuration  31 . 
     The rear end of the grill assembly  34  is received in a recess  37  of an additional mounting plate  38  that is affixed to the hull under portion  12  by threaded fasteners  39  and further fasteners  41  that are connected to an extension piece of the mounting plate  38  that defines the recess  37 . It will be seen from FIG. 3 that this then provides a fairly wide and elongated inlet opening for the water inlet passage  32 . 
     Referring now to the construction of the silencing extension assembly  27 , by reference primarily to FIGS. 2-4, it includes a mounting flange portion, indicated generally by the reference numeral  42 . This flange portion  42  has lugs  43  that receive threaded fasteners  44  for securing the mounting bracket to a further mounting plate  45  that is fixed in a recess defined by the bulkhead  26  and the mounting plate  38 . 
     The mounting flange portion  42  further forms an annual groove  46  in which an elastic sleeve  47  is positioned. Rearwardly of this, the mounting flange portion  42  has a recess  48  that receives an extension  49  of the impeller housing  14  (FIG.  4 ). This construction provides a continuous water flow path through the silencing extension assembly  27  best seen in FIG.  2 ). That is, the silencing extension assembly  27  and the mounting plate  45  define a continuous opening  51  extending rearwardly of the bulkhead  26 . This passageway is substantially the same diameter as that of the portion  52  of the impeller housing  14  that surrounds the impeller  22 . This has a length L 5  which is comprised of the segment L 4  which comprises the length of the portion of the continuous opening  51  in the mounting plate  45 , the length L 1  which is the combined length of the mounting flange portion  42  and the elastic sleeve  47  and the length L 3  which comprises the remainder of the length downstream of the elastic sleeve  47  and upstream of the impeller  22 . The impeller length L 2  is approximately equal to about 50 mm while the length L 5  is about 80 mm. In other words, the length L 5  is substantially greater than the length of the impeller  22  and in fact nearly double that length. This provides very, very effective silencing and isolation of pulsation damping in addition to the damping effect caused by the elastic sleeve  47 . 
     As shown in FIGS. 1 and 2 an impeller shaft  53  that extends forwardly through the water inlet passage  32  for its coupling to the output shaft of the engine  17  through a surrounding protective sleeve (not shown). 
     FIGS. 6 and 7 show another embodiment of the invention, which is similar in many regards to the embodiment thus far described. Where the same components are employed, they have been identified by the same reference numerals and will not be described in more detail. This embodiment, however, permits greater latitude in adjustment of the length of the various components leading up to the impeller  22 . 
     In this embodiment, a first mounting flange  101  is affixed to the bulkhead  26  by means of threaded fasteners comprised of studs  100  threaded into the mounting flange and nuts  102  received thereon. This mounting flange  101  has a water flow opening  103  that has substantially the same diameter as the remaining openings leading up to the impeller  22  and the inner diameter  52  of the impeller housing  21 . 
     Affixed to this mounting flange  101  is a spacer flange  104  that is fixed to the mounting flange  101  by threaded fasteners  105 . The spacer flange  104  has a stepped opening  106  in which an elastomeric sleeve  107  is received. It should be seen that this sleeve  107  actually extends forwardly within a recess  108  of the mounting flange  101  so that the elastic sleeve  107  can have a greater length than the previously described embodiment. In this embodiment the impeller housing  14  has an outer flange against which the threaded fasteners  105  act to secure the impeller housing  14  to the spacer flange  104  and thus to the mounting flange  101  and the bulkhead  26 . 
     In addition, the rear portion of the spacer flange  104  is provided with a recess  109  that receives an extending portion  111  of the impeller housing  14 . This extending portion  111  backs up the elastic sleeve  107  and holds it in place. 
     The impeller housing  14  is formed primarily from aluminum or an aluminum alloy. Therefore a suitable lining material  112  such as a stainless steel sleeve may be provided around the inner surface of the impeller housing portion  14 . This provides corrosion protection and reduced cost. The lining sleeve  112  has an inner diameter  113  that is the same as the flow opening  103  and the elastic sleeve  107  and the diameter  52  of the impeller housing  21  Therefore, there is provided a flow length consisting of the dimensions L 1  and L 3  provided by the mounting sleeve  104  and a part of the impeller housing formed by the extension  111 . This combined length is substantially greater than the length L 2  of the impeller  22 . In this particular embodiment, these lengths are equal to approximately 60 mm, which is greater than the length of the impeller, which is 55 mm (L 8 ). Of course, the length of the intake passage  103  formed in the mounting rings  101  further adds to the silencing effect. 
     These drawings further show how a nacelle and straightening vane section  114  of the jet propulsion unit  18  is connected to the impeller housing  21  by threaded fasteners  115 . A tongue  116  of the nacelle and straightening vane section  114  fits into a groove  117  in the rear of the impeller housing  21  for ease of assembly and alignment. A similar tongue and groove arrangement is provided in the connection at the rear of the nacelle and straightening vane section  114  to the discharge nozzle section  23 . The nacelle and straightening vane section  114  has a flow diameter  118  that is the same as those upstream flow diameters. 
     Thus, from the foregoing description is should be readily apparent that the features of the invention provide a very effective silencing for the jet propulsion unit for powering a watercraft that is particularly adept for use in personal watercraft. It is to be understood, however, that 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.