Abstract:
A marine jet drive with a wall structure forming an intake duct forward of a rotatable impeller, a drive shaft extending across part of the intake duct and coupling an engine to the impeller, a shaft sleeve secured to the wall structure, and a seal at the rear end of the shaft sleeve, the shaft sleeve and seal isolating the drive shaft from water and debris. Certain preferred embodiments include: a seal cartridge between the shaft sleeve and the impeller hub; a cooling feature; an annular-groove-and-pin cartridge-retention arrangement; a readily-releaseable sealing connection to the shaft sleeve; and a debris-cutting device.

Description:
RELATED APPLICATIONS 
     This is a divisional of Ser. No. 09/028,735, filed Feb. 24, 1998, now U.S. Pat. No. 6,045,418 which in turn is a divisional of Ser. No. 08/456,188, filed May 31, 1995, now U.S. Pat. No. 5,720,635, which in turn is a divisional of Ser. No. 07/699,336, filed May 13, 1991, now U.S. Pat. No. 5,421,753. 
    
    
     FIELD OF THE INVENTION 
     This invention is related generally to propulsion units for boats and, more particularly, to marine jet drives. 
     BACKGROUND OF THE INVENTION 
     Marine jet drives which propel vessels by means of water jets have long been known and used, and have certain significant advantages over the traditional external propeller units. A typical marine jet drive includes an engine-driven impeller which rotates inside an impeller housing. The impeller pumps water from below the vessel through an intake duct, and then pressurizes and expels the water through a diffusor housing and a nozzle behind the vessel. 
     Marine jet drives of the prior art have a number of problems and shortcomings, including as set forth below: 
     Design of marine jet drives involves many engineering considerations, such as: overall weight; tensile strength, compression, shear strength, elasticity, expansion and corrosivity of materials; operational tolerances; alignment considerations; and effective use of vessel space. Under the varying loads of operation of any marine jet drive, the propulsion system undergoes varying amounts of deformations. Engines, by virtue of the fact that they are typically mounted on resilient motor mounts, also produce movement which must be accommodated. Given these factors, it is necessary that marine jet drive systems accommodate such movements and deformations in one way or another. 
     Conventional jet drives need impeller tip clearances which are sufficient to allow for various deformations (including intake-duct deformation), engine-mount movement, shaft flexing and relative bearing movement under operational loads. In marine jet drive systems, the requirement of a water intake between the engine and the impeller typically means that the drive shaft, which extends across a portion of the intake duct, have considerable length. It is known that long unsupported spans of drive shafts require greater impeller-tip clearances than a shorter and/or supported spans of drive shafts. Larger impeller-tip clearances dramatically reduce the efficiency of jet drives. 
     The conventional jet drive, which has a drive shaft exposed to water in the intake duct, requires a shaft seal where the drive shaft passes through the transom (from the intake duct into the engine compartment within the vessel) in order to prevent ingress of water into the vessel. However, to avoid compromising such seals, drive shaft movement due to resilient motor mounts or deformation must be controlled. Drive shaft movement is typically restrained by a bearing and support structure between the engine and shaft seal assembly. Such bearing and seal assembly take up valuable vessel space by requiring that the engine be placed farther forward than would otherwise be necessary. 
     Use of metal structures has been considered favorable for reasons of strength and deformation resistance. However, use of metal parts in water, particularly sea water, produces electrolysis and corrosion, which have deleterious effects on longevity of conventional jet drives, on efficiency of operation, and in various other ways. Use of metal parts also contributes to high weight which has negative implications for performance. 
     Another prior art problem is the tendency of waterborne debris, particularly long-stranded debris, to become wrapped around exposed rotating drive shafts and impellers of conventional jet drives. This tends to reduce efficiency of operation, and can immobilize and endanger a vessel, particularly when its engine is turned off to clear the debris. 
     Another problem in various conventional marine jet drives is that they require frequent servicing and repair, and their disassembly is time-consuming. 
     OBJECTS OF THE INVENTION 
     It is accordingly a primary object of the present invention to provide a marine jet drive propulsion system that overcomes problems and shortcomings of the prior art, including those set forth above. 
     Another object of the invention is to provide an improved marine jet drive which more effectively utilizes vessel space by allowing engine placement in a position which is farther aft. 
     Another object of the invention is to provide an improved marine jet drive in which the drive shaft is protected from exposure to water. 
     Another object of the invention is to provide an improved marine jet drive which is protected from entanglement of long-stranded debris with the drive shaft. 
     Another object of the invention is to provide an improved marine jet drive which protects the impeller from entanglement with long-stranded debris. 
     Another object of the invention is to provide an improved marine jet drive allowing a wider selection of materials, including drive-shaft materials. 
     Still another object of this invention is to provide an improved marine jet drive having a reduced unit weight. 
     Another object of the invention is to provide an improved marine jet drive which is easily and quickly serviced. 
     Another object of the invention is to provide an improved marine jet drive which readily accommodates a substantial degree of misalignment due to movements and deformations during system operation and a greater variation in engine placement. 
     These and other objects of the invention will be apparent from the following descriptions and from the drawings. 
     SUMMARY OF THE INVENTION 
     This invention is an improved marine jet drive which overcomes various problems and shortcomings of the prior art including those referred to above. The marine jet drive of this invention is of the type which has forward and rearward ends and includes a rotatable impeller, a wall structure defining an intake duct forward of the impeller, the impeller being coupled to an engine via a drive shaft extending across a portion of the intake duct. 
     The improved marine jet drive includes a shaft sleeve secured with respect to the duct-forming wall structure and having front and rear sleeve ends, and a seal assembly at the rear end of the shaft sleeve, such that the drive shaft is isolated from water and debris. 
     The seal assembly preferably includes a seal cartridge between the shaft sleeve and the impeller. 
     In certain of such preferred embodiments, the impeller includes an impeller hub and a rotating outer housing member secured with respect to the impeller hub, and the seal assembly includes such outer housing member and the seal cartridge which is within the outer housing member. The seal cartridge preferably includes: a rotating seal element; a static seal element contacting the rotating seal element, the rotating and static seal elements have sealing faces engaged with one another; an inner housing member adjacent to and enclosing a portion of the static seal element and in releaseable sealing engagement with the shaft sleeve; and a spring extending between the inner housing member and the static seal element to urge the static seal element against the rotating seal element. 
     In highly preferred embodiments of the type just described, the inner housing member is retained within the outer housing member by an annular-groove-and-pin arrangement which allows free rotation of the outer housing member about the inner housing member but prevents the inner housing member from being axially separated from the outer housing member, thus retaining the seal cartridge in position during installation or disassembly of the drive unit from the vessel. Such annular-groove-and-pin arrangement most preferably involves the inner housing member having an outer surface with an annular groove on it, and at least one (and preferably more than one) retaining pin through the outer housing member and extending part way into the annular groove. The retaining pin or pins can be withdrawn from the annular groove to allow removal of the seal cartridge from the outer housing member. 
     In certain preferred embodiments, the shaft sleeve has a rear recess and the inner housing member referred to above has a forward portion which is removably inserted into the rear recess, the forward portion having a compressible seal engaging the shaft sleeve within the rear recess. This serves to provide sealing engagement while permitting release of the seal cartridge when an axial pull is applied to quickly and easily separate the inner housing from the shaft sleeve. 
     In highly preferred embodiments, the rotating outer housing member in which the seal cartridge is located has one or more radially-disposed ports therethrough which are adjacent to the static seal element. This allows the centrifugal action caused by rotation of the outer housing member to cause water to be drawn past the static seal element and out through the ports to facilitate cooling of the sealing surfaces. It is most preferred that the static seal element include cooling fins to facilitate heat transfer from the seal elements to the flowing water. This helps to keep the interfacing rotating and static seal elements from overheating. 
     Certain preferred embodiments of this invention include a debris-cutting device which serves to sever and reduce long-stranded incoming debris in order to prevent deleterious interactions with the impeller. The debris-cutting device includes one or more rotating blades which are secured to the outer housing member and at least one fixed blade secured with respect to the shaft sleeve in position such that the rotating blade or blades rotate past the fixed blade(s) to sever debris. 
     Highly preferred embodiments of this invention include a rear flexible coupling flexibly connecting the drive shaft to the impeller, and a front flexible coupling flexibly connecting the drive shaft to the engine. In such highly preferred embodiments, it is most preferred that the front flexible coupling be inside the vessel and directly coupled to the engine. 
     The marine jet drive includes, of course, an impeller housing around the impeller and a diffusor housing attached with respect to the impeller housing. In one embodiment of the dual-flexible-coupling marine jet drives of preferred embodiments of this invention, a bearing support structure which is disposed inside the diffusor housing and rotatively supports the impeller has the rear flexible coupling disposed within such bearing support structure. The bearing support structure is preferably rigidly attached to the diffusor housing by a plurality of radially disposed stator vanes. 
     In certain embodiments of the dual-flexible-coupling marine jet drives described above, the rear flexible coupling includes a drive shaft tube having at least one key for connection to the impeller, and the drive shaft is flexibly connected to the drive shaft tube by the rear flexible coupling. 
     The shaft sleeve and rearward seal assembly of the improved marine jet drive of this invention serve to isolate the drive shaft from the water in the intake duct across which the drive shaft extends. This provides a number of important advantages. The preferred embodiments of this invention which have front and rear flexible couplings provide additional important advantages. These varying advantages include those set forth below. 
     For example, the need for placement of a shaft seal assembly at the point of entry of the drive shaft into the vessel (i.e., through the transom) is eliminated, and this allows the engine to be farther aft—freeing valuable vessel space for other purposes. Furthermore, eliminating the need for a forward seal assembly (at the transom) facilitates use of a flexible coupling between the drive shaft and the engine. Use of a front flexible coupling becomes feasible because there is no forward seal assembly which would be compromised by the off-axis drive-shaft movements accommodated by use of a front flexible coupling. This in turn allows a wider choice of drive-shaft sizes and materials, which facilitates weight reduction. 
     The preferred embodiments with dual flexible couplings provide are particularly excellent in their accommodation of substantial deformation and movements which occur in jet drive operation, allowing a jet drive to accommodate a variety of vessels and engines. Jet drive systems in accordance with this invention may have many parts made of composites (plastics) rather than metals, and such systems provide excellent performance and exhibit excellent durability. 
     Another important advantage of the shaft sleeve and rearward seal assembly of this invention is that isolation of the drive shaft from the water eliminates any entanglement of debris with the drive shaft, and all the related problems. This arrangement also facilitates the mounting of a debris-cutting device to protect the impeller from such debris. 
     Among the other important advantages of the marine jet drive of this invention is the fact that it significantly facilitates assembly and disassembly of the drive unit with respect to the engine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view, taken along the drive-train centerline, of a marine jet drive in accordance with a preferred embodiment of this invention, showing its interior construction. 
     FIG. 2 is an enlarged fragmentary view of FIG. 1, showing additional details. 
     FIG. 3 is a further enlarged fragmentary view of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1-3 illustrate a marine jet drive according to this invention, located generally at the transom T of a vessel and generally above the keel line K, the direction of the jet stream J being rearward to propel the vessel forward as indicated by arrow F. 
     The jet drive includes the following general elements: an impeller housing  1  attached to an intake flange  2 ; a rotatable impeller  3  disposed in impeller housing  1 , its axis of rotation being aligned generally with keel line K; a diffusor housing  4  connected to impeller housing  1  and forming a water outlet port; a bearing support structure  5  disposed inside diffusor housing  4 ; a drive shaft  6  rotatively connecting impeller  3  with engine  7 ; a nozzle housing  8  attached to the diffusor housing  4  and forming a rearward-facing nozzle for jet stream J; an engine exhaust discharge tube  9  attached to bearing support structure  5 , a water intake duct  10  ahead of impeller housing  1  and attached to the vessel; and an intake grid  11  disposed in intake duct  10 . 
     Impeller  3  includes, among other things, an impeller hub  12 , an impeller bell  13  and a plurality of impeller blades  14  radially extending from the impeller bell  13  and terminating in blade tips  16 . A circular wear-ring insert  15  is inserted coaxially, snugly fitting the inside of impeller housing  1  such that impeller blade tips  16  extend to within close proximity of the inner surface  17  of wear-ring insert  15 . Blades  14  are advantageously positioned to promote fluid flow from intake duct  10  to diffusor housing  4  when impeller  3  rotates. Wear-rings of varying sizes and shapes may be selected depending on desired performance requirements of the jet-drive application. Such variations are possible without affecting the size and shape of impeller housing  1  or diffusor housing  4 . 
     Diffusor housing  4  supports bearing support structure  5  by a plurality of stator vanes  18  which are radially disposed between diffusor housing  4  and bearing support structure  5 , as seen in FIG.  1 . Stator vanes  18  are advantageously positioned to recover the rotational energy imparted by impeller  3 . 
     Impeller  3  is supported on a shaft tube  19  as shown in FIG.  2 . Impeller hub  12  accepts a split tapered bushing  20  in a tapered recess, and split tapered bushing  20  in turn fits over shaft tube  19 . An impeller lock nut (or “rotating outer housing member”)  21  is secured with respect to impeller hub  12  by threaded connection (see threads  23 ) onto shaft tube  19 , thereby wedging impeller hub  12  against split tapered bushing  20  and shaft tube  19 . Impeller lock nut  21 , which is a part of impeller  3 , also serves as the aforementioned rotating outer housing member of a seal assembly. The seal assembly also includes a seal cartridge  51 , hereafter described. An abutment  22  on shaft tube  19  prevents impeller hub  12  from moving rearward as impeller lock nut  21  is tightened. A thread  32  on tapered bushing  20 , permits the application of releasing force by means of a release nut (not shown) against impeller hub  12  to release tapered bushing  20  and free impeller hub  12  from shaft tube  19 , to provide a quick installation and release method for installing and removing impeller  3 . Impeller torque is transmitted via two or more keys, including at least one outer key  24  between impeller hub  12  and tapered bushing  20  and at least one inner key  25  between tapered bushing  20  and shaft tube  19 . Tapered bushing  20  is oriented to cause the thrust in forward direction F which is generated by the rotation of impeller  3  to force impeller  3  more tightly onto tapered bushing  20 . 
     Shaft tube  19  supports impeller  3 , as shown in FIGS. 1 and 2, and is suspended by a forward bearing  26 , a rear bearing  27 , and a thrust bearing  28 . Rear bearing  27  and thrust bearing  28  provide axial lock-up of shaft tube  19 . The thrust force of impeller  3  is transmitted via tapered bushing  20  to shaft tube  19  by thrust bearing  28  to a bearing support  29  that also supports forward bearing  26 . Bearing support  29  is affixed to bearing support structure  5  with a plurality of fasteners  30  at the interface between bearing support structure  5  and bearing support  29 . Rear bearing  27  is supported directly by a recess  31  in bearing support structure  5 . This support method fixes impeller  3  rigidly but rotatively in relation to impeller housing  1  and allows for closer tolerances between impeller tips  16  and wear-ring insert inner surface  17 , improving the efficiency of the jet drive. 
     Drive shaft  6  is coupled at its forward end to engine  7  by means of a front flexible coupling  33  inside the vessel. Drive shaft  6  is coupled at its rearward end to shaft tube  19  by means of a rear flexible coupling  34  inside a cavity  35 . 
     At the rearward end, shaft tube  19  is split perpendicularly (to the axis of rotation) at the largest diameter of cavity  35  to facilitate installation of rear flexible coupling  34 . The forward wall of cavity  35  is formed by a flange  36  of shaft tube  19 . Flange  36  transmits the thrust load to thrust bearing  28  and serves as the driven part of flexible coupling  34 . A driving flange  37  of flexible coupling  34  is suspended in cavity  35  via a flexible element  38 . Driving flange  37  is connected to flexible element  38  by a plurality of fasteners  38   a . Driving flange  37  has a hub  39  that is provided with a spline connection  40  which engages drive shaft  6 . A flexible seal  82  is placed between shaft tube  19  and drive shaft  6  to prevent water entry into coupling cavity  35 , while drive shaft  6  may move as permitted by coupling  34 . Coupling cavity  35  is further formed by a rear flange  41  with a forward protruding rim  42  engaging forward flange  36  of shaft tube  19  with a close tolerance register to maintain alignment of rear bearing  27  with forward bearing  26  and thrust bearing  28 . Rear flange  41  is connected to flexible element  38  and shaft tube  19  by a plurality of fasteners  38   b . At the other side of rear flange  41  is a hub  43  supporting rear bearing  27 . 
     At the forward end of drive shaft  6 , flexible coupling  33  is similar to rear flexible coupling  34 , with the driven flange  44  being attached to drive shaft  6  with a spline connection  40  similar to the one in hub  39 . A driving flange  45  is attached to the output shaft of engine  7 , which is placed on resilient engine supports (not shown) to limit transmission of engine vibrations to the vessel. 
     Misalignment due to various deformations and engine movements during operation are absorbed by the combination of front and rear flexible couplings  33  and  34  and front and rear spline connections  40 . All such misalignments are absorbed at the ends of drive shaft  6  via flexible couplings  33  and  34 ; no further components are necessary to accommodate misalignment. Spline connections  40  provide torque transmission and permit axial movement between each of flanges  37  and  44  and drive shaft  6 . Quick release of drive shaft  6  from flexible couplings  33  and  34  is achieved by simple extraction of drive shaft  6  from flanges  37  and  44 . 
     The marine jet drive further includes a shaft sleeve  46  in intake duct  10 . Shaft sleeve  46  encloses drive shaft  6  and is supported by an upper wall  47  of intake duct  10 . Sleeve  46  isolates rotating drive shaft  6  from water and debris that might otherwise be ingested by intake duct  10  and get wrapped around drive shaft  6 . Additionally, as no water from intake duct  10  comes in contact with drive shaft  6  by virtue of shaft sleeve  46  and seal cartridge  51 , which is located between impeller  3  and shaft sleeve  46 , drive shaft  6  may be made of materials (alloys or composites) chosen purely for their strength (or light weight) and not for corrosion protection. Higher strength materials permit smaller and lighter drive shafts. The inner bore of shaft sleeve  46  may be tapered, thereby providing a larger bore diameter toward the forward end of drive shaft  6  to allow for increased drive shaft articulation near front flexible coupling  33 . 
     The seal assembly, including rotating outer housing member (or “impeller locking nut”)  21  and seal cartridge  51 , seals shaft sleeve  46  with respect to impeller  3 . Such seal assembly prevents water in intake duct  10  from entering shaft sleeve  46  between the forward end of rotating impeller hub  12 , where rotating outer housing member  21  is located, and the end  50  of fixed shaft sleeve  46 . Thus, shaft sleeve  46  and such seal assembly serve together to keep drive shaft  6  dry and isolated from the water and any debris. Given that shaft sleeve  46  is open to the interior of the vessel, the seal assembly serves to prevent water not only from entering shaft sleeve  46 , but consequently also from entering the vessel. 
     Seal cartridge  51 , which is best illustrated in FIG. 3, includes several parts housed within rotating outer housing member  21  of the seal assembly. These include a rotating seal element  54 , a static seal element  55 , an inner housing member (or “retaining member”)  56 , a coil spring  60 , and certain other elements hereafter described. Rotating seal element  54  is an annular member spaced from and encircling drive shaft  6  in a position inside outer housing member (or “impeller locking nut”)  21  and forward of shaft tube  19 . Rotating seal element  54  is sealingly secured with respect to outer housing member  21  (with which seal element  54  rotates) by an O-ring  54   a  (or other suitable sealing and securing means) in compression therebetween. 
     Static seal element  55  is an annular member immediately forward of rotating seal element  54 . Static seal element  55  has a rear sealing face  55   a  which is in compression sealing engagement with a forward sealing face  54   b  of rotating seal element  54 . Such compression sealing engagement is by virtue of spring  60  which extends axially between static seal element  55  and a rearward-facing inner ledge  56   a  of inner housing member  56 . Inner housing member  56  also includes a rearward-extending cup portion  56   b  which contains spring  60 . 
     Inner housing member  56  also includes a main portion  56   c  which is forward of cup portion  56   b , and a forward portion  56   d  which is forward of main portion  56   c . Main portion  56   c  has an outer surface  56   e  which forms an annular groove  56   f . Forward portion  56   d  is received within a rear recess  50   a  of end  50  of shaft sleeve  46 . Forward portion  56   d  of seal cartridge  51  includes a groove  56   g  on its outer surface which holds an O-ring  56   h  (or other suitable sealing and securing means) in compression fit within rear recess  50   a . More specifically, rear recess  50   a  is bounded by annular inner wall  50   b  which includes a shallow annular indent  50   c  on which O-ring  56   h  is located, in compression against inner housing member  56 . 
     Retaining pins  57  extend radially through outer housing member (or “impeller locking nut”)  21  such that their ends extend partially into annular groove  56   f.  This serves to hold seal cartridge  51  axially in place within outer housing member  21  during disassembly of the jet drive unit; however, when the jet drive is assembled and in operation, the ends of retaining pins  57  move freely around groove  56   f  as impeller  3  and outer housing member  21  rotate. 
     Main portion  56   c  of inner housing member  56  has an annular forward abutment surface  56   i  which engages the rear surface  50   d  of sleeve end  50 . This engagement defines the relative axial positions of seal cartridge  51  with respect to shaft sleeve  46 , and serves to hold seal cartridge  51  in position relative to outer housing member  21  such that retaining pins  57  are aligned with groove  56   f.    
     Spring  60  urges rear sealing face  55   a  of static seal element  55  against and in sealing engagement with forward sealing face  54   b  of rotating seal element  54 . The heat generated by friction between sealing faces  55   a  and  54   b  are conducted through static seal element  55  to cooling fins  61  which extend radially on the outer surface of static seal element  55 . Water from intake duct  10  is pulled in from the gap between outer housing member  21  and sleeve end  50 , then is pulled past cooling fins  61 , and exits by means of centrifugal force through a plurality of radially disposed holes  62  in outer housing member  21 . Rotational lock-up is provided between static seal element  55 , inner housing member  56  and sleeve end  50  to prevent the components from turning with rotating seal element  54 . 
     As best shown in FIGS. 2 and 3, a cutting device  53  is provided which includes one or more rotating blades  63  mounted on the rotating outer housing member (or “impeller lock nut”)  21 , and one or more stationary blades  64  which are mounted on shaft sleeve  46  and are further secured from rotating by one or more back stops  52 . Cutting device  53  serves to cut any long-stranded debris that has passed through intake grid  11  to prevent such debris from wrapping itself around impeller  3  and causing cavitation and/or imbalance. 
     While the principles of this invention have been described in connection with specific embodiments, it should be understood clearly that these descriptions are made only by way of example and are not intended to limit the scope of the invention.