Abstract:
A propeller for a trolling motor has an inner hub and an outer hub. The inner hub is made of a synthetic elastomer so that relative rotational movement between the outer hub and a propeller shaft is permitted. This relative movement dampens the reactive forces during an impact between blades of the propeller and submerged objects, such as weeds. The elastic deformability of the inner hub also reduces noise that can be caused by imbalances contained in the propeller.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is generally related to a trolling motor propeller and, more specifically, to a trolling motor propeller which is provided with an elastically deformable central hub which decreases reactive forces when the propeller strikes an object. 
         [0003]    2. Description of the Related Art 
         [0004]    Many different types of propellers are known to those skilled in the art. Some marine propellers are intended for use with trolling motors. These propellers are typically made of a relatively hard plastic material or metal. Trolling motors typically use electric motors, in the range of 0.26 horsepower to 1.18 horsepower, to drive the propeller. 
         [0005]    One desirable quality of a trolling motor is to provide motive force for a marine vessel without generating significant noise. Noise can be generated by the trolling motor when the blades of its propeller strike underwater objects, such as weeds. 
         [0006]    U.S. Pat. No. 4,311,470, which issued to Blanchard on Jan. 19, 1982, describes a trolling motor which includes a shaft extending vertically under normal operating conditions and having a lower end. The shaft is supported by a boat hull. An electric motor is fixedly connected to the lower end of the vertical shaft and includes an output shaft. 
         [0007]    U.S. Pat. No. 4,482,298, which issued to Hannon et al. on Nov. 13, 1984, describes a weedless propeller. The propeller, which is intended for use with a trolling motor, comprises a major hub having a plurality of propeller blades. The rearward end of the major hub is bluntly terminated immediately aft the trailing edge of the blades at the root of the blades. A secondary hub is connected to the forward end of the primary hub. The junction between the forward end of the secondary hub and the shroud of the engine or motor driving the propeller is spaced a substantial distance from the major hub and blades. 
         [0008]    U.S. Pat. No. 4,861,313, which issued to Zeiser et al. on Aug. 29, 1989, describes an elastomeric shaft coupling for concentric shafts. A dual concentric shaft coupling arrangement is provided with both inner and outer rotatable assemblies. An inner assembly comprises an inner rotatable driving member, an inner rotatable driven member and an inner rotatable intermediate member that is connected therebetween. An outer assembly comprises an outer rotatable driving member, an outer rotatable driven member and an outer rotatable intermediate member connected therebetween. 
         [0009]    U.S. Pat. No. 5,352,093, which issued to Hannon et al. on Oct. 4, 1994, describes a weedless propeller. The propeller is intended for use on low power motors, such as two horsepower or less electric trolling motors, and is provided with three or more blades on a hub wherein the hub diameter to the blade length is in the ratio of at least 1.250 to 1. The hub diameter to blade length ratio is such as to produce a propeller having increased performance and is substantially weedless. 
         [0010]    U.S. Pat. No. 5,372,480, which issued to Van Meter et al. on Dec. 13, 1994, describes a replaceable and foldable blade boat propeller. The blades are easily removable from the propeller hub on an individual basis to permit quick replacement for repair and/or for substituting blades of different pitch comprising a hub adapted to fit over and attach to a driveshaft. It also comprises a plurality of removable blades positioned around the hub and extending radially therefrom. Each of the blades comprises a water engaging blade portion and a rigid tang extending from the base and of such blade portion. 
         [0011]    U.S. Pat. No. 6,024,615, which issued to Eichinger on Feb. 15, 2000, discloses a vibration absorbing apparatus for a rotating system. The system incorporates an inertia mass that is disposed within a hollow portion of an impeller structure. The inertia mass is attached to one or more elastomeric members which are, in turn, attached to an inside surface of a tubular portion of the impeller structure. The annular inertia mass and its elastomeric legs are particularly designed to dampen and counteract a particular frequency at which the propulsion system vibrates when the internal combustion engine is operated at idle speed. 
         [0012]    U.S. Pat. No. 6,478,543, which issued to Tuchscherer et al. on Nov. 12, 2002, discloses a torque transmitting device for mounting a propeller to a propeller shaft of a marine propulsion system. The device provides an adapter that is attached in torque transmitting relation with a propulsor shaft for rotation about a central axis of rotation. The first insert portion is attached in torque transmitting relation with the adapter and a second insert portion is attached in torque transmitting relation with a hub of the propulsor hub which can be a marine propeller or an impeller. A third insert portion is connected between the first and second insert portions and is resilient in order to allow the first and second insert portions, to rotate relative to each other about the central axis of rotation. 
         [0013]    U.S. Pat. D473,567, which issued to Campbell on Apr. 22, 2003, describes a trolling motor propeller. This design patent shows one particular ornamental design for a trolling motor propeller and also illustrates several concepts regarding the construction of the propeller. 
         [0014]    The patents described above are hereby expressly incorporated by reference in the description of the present invention. 
         [0015]    It would be a significant benefit if a trolling motor propeller could be provided which decreases the sound level caused by the trolling motor as a result of the propeller striking an underwater object or as a result of an imbalance of the propeller. These vibrational and impact noises detract from the enjoyment of fishing and can adversely affect the likelihood of fishing success. 
       SUMMARY OF THE INVENTION 
       [0016]    A propeller for a trolling motor, made in accordance with a preferred embodiment of the present invention, comprises an outer hub made of a first material, a plurality of blades attached to the outer hub, and an inner hub made of a second material. The outer hub is configured to be rotatable about a central axis. The inner hub is disposed radially inwardly of the outer hub and is shaped to receive a propeller shaft therethrough. The inner hub is configured to be rotatable about the central axis in synchrony with the outer hub. 
         [0017]    The second material, of the inner hub, is more elastically deformable than the first material, of the outer hub, in a preferred embodiment of the present invention. The second material can be an elastomeric material such as a natural or synthetic rubber compound. The first material, in a preferred embodiment of the present invention, can be plastic or metal. 
         [0018]    The inner hub can be alternatively configured to be removably inserted into the outer hub or co-molded with the outer hub. When the propeller is attached to a trolling motor, the propeller shaft can be inserted through a central opening of the inner hub. The propeller shaft can be generally coaxial with the central axis. In some embodiments of the present invention, the inner hub can be provided with a plurality of discontinuities that are formed on a generally cylindrical outer surface of the inner hub. These discontinuities are shaped to be received in symmetrical discontinuities formed on an inner cylindrical surface of the outer hub. In applications where the inner hub is configured to be removably inserted into the outer hub, these matching discontinuities increase the gripping effect between the inner and outer hubs. When the inner and outer hubs are co-molded, on the other hand, the outer surface of the inner hub firmly adheres to the inner surface of the outer hub. However, in certain applications of the present invention, discontinuities can also be provided in order to enhance the degree of adherence between these meeting surfaces. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The present invention will be more fully and completely understood from a reading of the description of the preferred embodiment in conjunction with the drawings, in which: 
           [0020]      FIG. 1  is a side section view of a propeller for a trolling motor made in accordance with a preferred embodiment of the present invention; 
           [0021]      FIG. 2  shows an inner hub with a central opening formed therethrough; 
           [0022]      FIG. 3  shows the inner hub of  FIG. 2  with a propeller shaft extended through the central opening; 
           [0023]      FIG. 4  is an end view of the inner hub with a plurality of discontinuities formed on an outer surface of the inner hub; 
           [0024]      FIG. 5  is a side view of the inner hub shown in  FIG. 4 ; and 
           [0025]      FIGS. 6 and 7  illustrate an advantage of the present invention during an impact between propeller blades and a submerged object. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    Throughout the description of the preferred embodiment of the present invention, like components will be identified by like reference numerals. 
         [0027]      FIG. 1  illustrates a section view of a propeller made in accordance with a preferred embodiment of the present invention. The trolling motor propeller  10  comprises an outer hub  14  that is made of a first material and configured to be rotatable about a central axis  18 . Blades  20  are attached to the outer hub  14 . An inner hub  30 , is made of a second material. The inner hub  30  is disposed radially inwardly of the outer hub  14 , as shown in  FIG. 1 . The inner hub  30  is shaped to receive a propeller shaft  34  therethrough. The inner hub  30  is configured to be rotatable about the central axis  18 . 
         [0028]    The second material used to make the inner hub  30  is more elastically deformable than the first material used to make the outer hub  14 . As an example, the inner hub  30  can be made of a synthetic elastomer, such as rubber. The outer hub  14  is typically made of a relatively hard plastic material or a metal, such as aluminum. 
         [0029]    In certain embodiments of the present invention, the inner hub  30  is co-molded with the outer hub  14  to form an integral structure with the outer surface  40  of the inner hub  30  being permanently attached in adherence to the inner surface  42  of the outer hub  14 . Alternatively, the inner hub  30  can be configured to be removably inserted into the outer hub  14 . 
         [0030]      FIG. 1  shows the propeller shaft  34  inserted through a central opening  46  of the inner hub  30 . The propeller shaft  34  is maintained in a generally coaxial relationship with the central axis  18  by the shape and size of the central opening  46  as will be described in greater detail below. 
         [0031]    The inner hub  30  can be provided with a plurality of discontinuities formed on its generally cylindrical outer surface  40 . This will be described in greater detail below. 
         [0032]      FIG. 2  is a cross-section view of the elastomeric inner hub  30 . The central opening  46  is formed with a plurality of protrusions  50  that extend circumferentially around the internal surface of the central opening  46 . These protrusions  50  define an elongate opening that is coaxial with the central axis  18  described above. The inwardly directed outer surfaces of the protrusions  50  are shaped and sized to receive the propeller shaft  34 , which is described above in conjunction with  FIG. 1 , in a generally interference relationship. As the propeller shaft  34  is inserted into the opening  46 , along the axis  18 , the inwardly directed surfaces of the protrusions  50  cooperate with each other to maintain the propeller shaft  34  in coaxial relation with the central axis  18  and to maintain that relationship with regard to its position in the inner hub  30 . 
         [0033]      FIG. 3  shows the inner hub  30  with the propeller shaft  34  inserted into the opening along the central axis  18 . As can be seen, the inwardly facing surfaces of the protrusions  50  are disposed in interfering relation with the propeller shaft  34  to hold it in place along the central axis. These surfaces  56  are slightly distorted and disposed in frictional contact with the outer surface of the propeller shaft  34  and, as a result of the elastic deformability of the second material, a radially inward force is provided by the surfaces  56  of the protrusions  50 . 
         [0034]    With reference to  FIGS. 1 and 3 , the propeller shaft  34  is also held in place relative to the inner hub  30  by a pin  60  and a nut  64 . The attachment of a propeller shaft to a trolling motor propeller with a pin  60  and a nut  64  is generally known to those skilled in the art and will not be described in greater detail herein. 
         [0035]      FIG. 4  is an end view of the inner hub  30 , showing the central opening  46  and the central axis  18 . In the embodiment shown in  FIG. 4 , the outer surface  40  of the inner hub  30  is provided with a plurality of exemplary discontinuities  60 . In this example, the discontinuities  60  extend along the length of the inner hub  30  and are generally parallel with the central axis  18 . However, it should be understood that alternative shapes and configurations of the discontinuities  60  can be implemented in alternative embodiments of the present invention. 
         [0036]      FIG. 5  is a side view of the illustration shown in  FIG. 4 . It illustrates the positions of the discontinuities  60  on the outer surface  40  of the inner hub  30 . 
         [0037]      FIGS. 6 and 7  are intended to illustrate an advantage of the present invention. In  FIG. 6 , the inner hub  30  is shown within the outer hub  14 . It should be understood that the outer surface  40  of the inner hub  30  and the inner surface  42  of the outer hub  14  are adhered to each other. If these two hubs are co-molded, these surfaces are permanently bonded to each other. If, alternatively, the inner hub  30  is disposed within the outer hub  14  in a removable manner, the shapes of the surfaces and the forces provided by the pin  60  and nut  64  maintain an intimate contact between the outer surface  40  and the inner surface  42 . These surfaces,  40  and  42 , are not intended to move relative to each other. To illustrate this beneficial effect of the present invention, two construction lines,  80  and  82 , are shown in  FIG. 6 . With no torsional force exerted on the propeller or shaft, lines  80  and  82  are collinear as shown. 
         [0038]      FIG. 7  shows the result of relative rotational movement between the outer hub  14  and inner hub  30 . Dashed lines  80  and  82  in  FIG. 7  show the original positions of these lines before relative rotational forces caused the outer hub  14  and inner hub  30  to rotate relative to each other. Solid lines  80  and  82  in  FIG. 7  show the result of this relative movement. The outer hub  14  is rotated in a clockwise direction relative to the propeller shaft located in the central opening  46 . This rotation is about the central axis  18 . The inner hub  30  remains rigidly attached to the propeller shaft and its outer surface  40  remains rigidly attached to the inner surface  42  of the outer hub  14 . This is illustrated by the point  86  which remains at its relative position with respect to the radially outer end of line  80  and radially inner end of line  82 . This also illustrates no relative movement between surfaces  40  and  42 . However, since the outer hub  14  rotated in a clockwise direction and the propeller shaft did not, elastic deformation occurs within the structure of the inner hub  30 . This is represented by the non-linear shape of solid line  80  in  FIG. 7  compared to its linear configuration in  FIG. 6 . This elastic deformation of the inner hub  30  absorbs the impact when a propeller blade  20  strikes an underwater object, such as a weed. Following that impact, the resiliency of the elastomeric material used to make the inner hub  30  elastically returns the outer hub  14  to its original position relative to the inner hub  30 . In other words, solid lines  80  and  82  in  FIG. 7  will return to the positions represented by dashed lines  80  and  82  as a function of the resilience of the elastically deformable material used to make the inner hub  30 . 
         [0039]    With reference to  FIGS. 1-7 , it can been seen that a propeller for a trolling motor made in accordance with a preferred embodiment of the present invention comprises an outer hub  14  of a first material, such as plastic or metal, and a plurality of blades  20  attached to the outer hub  14 . The outer hub  14  is configured to be rotatable about a central axis  18 . An inner hub  30  is made of a second material, such as a synthetic elastomer, and is disposed radially inwardly of the outer hub  14 . The inner hub  30  is shaped to receive a propeller shaft  34  therethrough. The inner hub is configured to be rotatable about the central axis  18  with the outer hub  14 . The second material, used to form the inner hub  30 , is more elastically deformable than the first material used to form the outer hub  14 . 
         [0040]    In certain embodiments of the present invention, the inner hub  30  is configured to be removably inserted into the outer hub  14 . However, in other embodiments of the present invention, the inner hub  30  is co-molded with the outer hub to provide a permanent adhesion between the outer surface  40  of the inner hub  30  and the inner surface  42  of the outer hub  14 . The propeller  10  is attached to a trolling motor by inserting the propeller shaft  34  through a central opening  46  of the inner hub  30 . The propeller shaft  34  is generally coaxial with the central axis  18 . In certain embodiments of the present invention, particularly when the inner hub  30  is removably attached to the outer hub  14 , a plurality of discontinuities can be formed on a generally cylindrical outer surface  40  of the inner hub  30 . This enhances the attachment between the outer surface  40  of the inner hub  30  and the inner surface  42  of the outer hub  14 . 
         [0041]    Although the present invention has been described with particular specificity and illustrated to show a preferred embodiment, it should be understood that alternative embodiments are also within its scope.