Marine propulsion – Screw propeller – Shafting
Reexamination Certificate
2000-03-31
2002-04-02
Swinehart, Ed (Department: 3617)
Marine propulsion
Screw propeller
Shafting
Reexamination Certificate
active
06364725
ABSTRACT:
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 engagem
Jansson & Shupe & Munger Ltd.
Swinehart Ed
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