Abstract:
A seal adapter for reducing the escape of exhaust gases between an outboard motor and a propeller includes a substantially hollow cylindrical connecting member ( 71 ) having a shoulder ( 84 ) for dividing the connecting member ( 70 ) into a plurality of sections. A seal ring ( 80 ) is associated with one of the sections for engaging with an annular recess ( 76 ) located within the propeller hub ( 74 ) to provide a substantially tight seal.

Description:
This application claims priority from U.S. Provisional Patent Application No. 60/350,471, filed Nov. 13, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to seals, and particularly to labyrinth seals for marine propulsion out-drives, and more particularly to reduce the flow of engine exhaust between the outdrive stationary housing and the rotating propeller hub. 
     2. Description of the Related Art 
     A substantial number of marine craft outboard motors, and perhaps an equal number of marine craft using inboard/outboard drives, the engine exhaust is ducted through the lower unit of the outdrive and out through the hub of the propeller. The dimensions of the lower unit housings vary from manufacturer to manufacturer and often require specific dimensioned propellers to provide the proper fit between the propeller hub and the outdrive or lower unit housing. This seal is crucial to prevent exhaust gases from being discharged on the suction side of the propeller blades which reduces propeller efficiency. In the industry, this seal between the propeller hub and the lower unit housing is referred to as a labyrinth seal. Because this seal is important to performance, a large number of propeller models are required to fit the various out-drives. The end result is retailers must invest in substantial inventory to supply replacement propellers. Moreover, purchasers often encounter difficulties finding the proper replacement propeller for their particular drive model. 
     SUMMARY OF THE INVENTION 
     The purpose of this invention is to provide an adapter for properly creating the labyrinth seal between a propeller hub and the lower unit of an outdrive. That is to say, for a given propeller, the proper labyrinth seal may be provided by an inexpensive adapter specially configured to match that particular propeller to the outdrive. 
     The labyrinth seal adapter includes a polymeric ring adapted to be attached to the end of the propeller hub and is configured to seal with the lower unit of the outdrive. In one embodiment, the adapter may be configured to be received over the end of the propeller hub, and alternatively in another embodiment, be received within the end of the propeller hub. The profile of the adapter is such that it provides a transition from the propeller hub end to just inside the end of the outdrive lower unit to direct engine exhaust gases through the propeller hub rather than upstream of the propeller blades. 
     The advantage is a substantial cost savings achieved by a reduction in inventory. The labyrinth seal adapter is matched with the desired universal propeller to provide the proper seal to a specific manufacturer&#39;s lower unit housing configuration. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     FIG. 1 is a perspective view of a portion of a boat outdrive lower unit and propeller; 
     FIG. 2 is a fragmentary section view of the lower unit and propeller shown in FIG. 1; 
     FIG. 3 is a fragmentary section view of a lower unit and a propeller having the labyrinth seal adapter of the instant invention; 
     FIG. 4 is a fragmentary section view illustrating one embodiment of the invention and how it is attached to the propeller hub; and 
     FIG. 5 is a fragmentary section view illustrating another embodiment of the invention and an alternate attachment method to the propeller hub. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For purposed of the following description, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal” and derivatives thereof shall relate to the invention as oriented in FIG.  3 . However, it is to be understood that the invention may assume various alternative orientations except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the specification and any appended claims. Specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. 
     Referring to the drawing figures, a lower unit  10  of a marine propulsion unit  12  is shown having a propeller  14  attached thereto. An engine (not shown) is provided at an opposite end of the marine propulsion unit  12  for driving the propeller  14  through a transmission (not shown). Driving rotation of the propeller  14  is selectively reversible by means of the transmission to provide for operation of the craft in forward and reverse directions as desired. The exhaust gases from the engine are conducted downwardly though passage  16  in the lower unit  10  for discharge underwater through the hub  18  of the propeller  14 . As generally shown in the drawing figures, the propeller  14  is carried by the generally horizontal propeller shaft  20  which is journaled in the exhaust passage  16  contained within housing  22 , and projects rearwardly through the opening  24 . The horizontal propeller shaft  20  is splined to provide a positive rotational coupling with the propeller hub. 
     The propeller  14  is separable or independently replaceable relative to the horizontal propeller shaft  20  and includes an outer hub sleeve member  26  which carries the blades  28  and an inner hub sleeve member  30  spaced radially inwardly from and connected to the outer hub sleeve member  26  by one or more circumferentially spaced vanes  32 . A number of different mechanisms are now available to couple the inner hub sleeve member to the propeller shaft and will not be discussed in any detail here. However, general reference is made to a semirigid coupling available through Michigan Wheel Corporation which allows the propeller hub to slip with respect to the propeller shaft when the propeller strikes a solid object during rotation. In the alternative, the inner hub sleeve member  30  may have a central cylindrical opening having internal splines configured to mate with and be received along the horizontal propeller shaft  20 . For the purposes of completeness, this more rigid and conventional coupling is illustrated. 
     Referring to FIG. 2, a conventional dedicated propeller  34  is shown which is specially configured such that the outside diameter (O.D.) of propeller end  36  is adapted to be received within the inside diameter (I.D.) of the end  38  of propeller housing  40 . The distance the leading end  36  of the propeller  34  is received within and overlaps with the lower unit housing  40  may vary depending upon other characteristics of the marine propulsion unit such as  12 , but it is anticipated the end  36  of the propeller may overlap by as little as one-eighth of an inch to as much as one inch with the end  38  of the lower unit propeller housing  40 . Moreover, the distance between the O.D. of the propeller end  36 , and the I.D. of the lower unit propeller housing  40  may also vary, ranging from as little as one thirty-second of an inch up to one quarter of an inch clearance. However, it is preferred to keep the gap as small as possible in order to keep the pressure differentials up and prevent the exhaust gases from escaping there between. 
     FIG. 3 illustrates one example where a propeller  50  is not properly dimensioned to mate with the end of the lower unit housing  52 . Here, as in FIG. 2, the propeller  50  is shown partially off the propeller shaft  54  to emphasize the difference in size between the leading edge  56  of the propeller hub  58  and the opening  60  of the lower unit housing  52 . In this instance, the labyrinth seal may not be formed well enough to prevent the escape of exhaust gases from the lower unit housing  52  and impact propeller performance. One embodiment of a labyrinth seal adapter  62  is shown attached to the leading end  56  of the opening  60  to provide the proper clearances to affect the labyrinth seal function. 
     FIG. 4 illustrates one example of a labyrinth seal adapter  70  contemplated to be within the scope of the invention where a substantially hollow connecting member  71  is used with the leading end  72  of a propeller hub  74 . In this particular embodiment, the propeller hub  74  is manufactured such that an annular recess  76  is defined in the inner diameter hub wall  78  spaced a predetermined distance from the leading end  72  of the propeller hub  74 . The annular recess  76  is configured to receive an annular rim or coupling ring  80  formed at one end  82  of the connecting member  71 . Spaced a specific distance from the end of the ring  80  is a shoulder  84  configured to provide the transition from the propeller hub  74  providing the labyrinth seal with the opening  60  mentioned above. The shoulder  84  abuts against the leading end  72  to provide a minimal space between the two to restrict the escape of exhaust gases. 
     The labyrinth seal adapter is manufactured of a semi-flexible material in order to facilitate a tight mechanical seal. Although in the drawing figure it is shown to provide a larger diameter end  86  than the leading end  72  of the propeller hub  74 , it should be understood the O.D. of the large diameter end  86  could also be smaller than the leading end  72  of the propeller hub  74  to provide the labyrinth seal with a smaller I.D. of the lower unit housing. The dimensional differences and variations with the transitions may very well be different depending upon the propeller used and the manufacturer of the lower unit housing. As seen in FIG. 4, this embodiment illustrates where the labyrinth seal adapter  70  is received within the I.D. of the propeller hub  74 . 
     FIG. 5 illustrates yet another embodiment where the labyrinth seal adapter may be designed to be attached over the O.D. of the propeller hub. In this embodiment, the propeller hub  90  has a leading end  92  fashioned to have a reduced O.D. cylindrical portion  94  terminating in a truncated conical-like tapered ring or rim  96  of slightly larger O.D., similar to the end of the labyrinth seal adapter  70  described above. In a reversal of components, the labyrinth seal adapter  98  shown in FIG. 5 is preferably formed from a flexible polymeric material housing  100  and has an O.D. which is formed to provide a transition from the propeller hub  90  to the appropriate diameter at the cavity  101  to create the correct labyrinth seal with an outdrive stationary housing (not shown). The internal wall  102  of the cavity  103  of the labyrinth seal adapter  98  includes a tapered annulus  104 , located substantially between cavity  101  and cavity  103 , adapted to be received over ring  96  and retain the labyrinth seal adapter  98  on the end  92  of the propeller hub  90 . Again, as in the previous embodiment, FIG. 5 illustrates an increase in the O.D. of the labyrinth seal to fit a smaller propeller hub with a larger I.D. of the lower unit housing. However, it should again be understood the transition could be a reduction in the diameter of the labyrinth seal to accommodate a larger propeller hub. 
     As briefly mentioned above, the purpose of the invention is to reduce the number of different model propellers necessary for a dealer to keep in stock. The labyrinth seal adapter provides an inexpensive way to adapt a particular propeller to the correct outdrive unit. The labyrinth seal adapters may be injection molded from polymeric material, or depending upon the particular coupling method, may also be die-cast or formed from powdered metal. In the latter case, screw fasteners may be used to attach the adapter directly to the propeller hub. Polymeric material is at the time of this writing the preferred material as the adapter can be pressure or snap fit onto the propeller hub without the need for screws or other separate mechanical fasteners. 
     The above description is considered that of the preferred embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the doctrine of equivalents. 
     The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: