Patent Publication Number: US-6220906-B1

Title: Marine propulsion assembly

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for Governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The invention relates to marine propulsion systems including drive shafts and propellers, and is directed more particularly to a marine propulsion system in which there is only a single drive shaft and two counter rotatable propellers. 
     (2) Description of the Prior Art 
     The use of counter-rotating propellers in marine propulsion systems is known. In particular, and referring to FIG. 1, such arrangements of propellers  10 ,  12  have found utility in torpedoes and unmanned undersea vehicles  14 , and are favored in view of their efficiency, quiet operation, and the fact that they are torque balanced. 
     Known systems, as shown in FIG. 2, include two propeller drive shafts  16 ,  18 , one for each propeller. Inasmuch as the two propellers  10 ,  12  typically are in axial alignment with each other, one of the drive shafts  18  is nested inside the other  16 . A drive source  20 , such as a motor or engine, drives the two shafts  16 ,  18 . Bearings  22  are required between the two shafts, as well as between the outer shaft  16  and the vehicle body, or other support structure  24 . Seals (not shown) are also required between the two shafts. 
     When an electric motor is used for the drive source  20 , the use of two counter-rotating shafts requires a relatively complex motor, typically requiring a hole through the motor in which the inner shaft is disposed, or a secondary outer case which allows the field to rotate as well as the outer shaft. 
     There is a need for a simpler structure with respect to the drive shaft component of the assembly and a structure which permits use of an ordinary electric motor. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a marine propulsion assembly wherein two propellers rotate in opposite directions and are driven by a single drive shaft. 
     With the above and other objects in view, as will hereinafter appear, a feature of the present invention is the provision of a marine propulsion assembly which includes a drive shaft, a first propeller fixed to the drive shaft and turnable therewith in a first direction, and an annular array of gear teeth disposed on the first propeller and turnable therewith. The assembly further includes a second propeller aligned with the first propeller, and an annular array of gear teeth disposed on the second propeller. Bevel gears are disposed between the first and second propellers and are each provided with a single array of teeth engaged with the first and second annular arrays of gear teeth. The bevel gears transmit rotation of the drive shaft and the first propeller to the second propeller, such that the second propeller turns in an opposite direction relative to the first propeller. 
     The above and other features of the invention, including various novel details of construction and combinations of parts, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular devices embodying the invention are shown by way of illustration only and not as limitations of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference is made to the accompanying drawings in which are shown illustrative embodiments of the invention, from which its novel features and advantages will be apparent, wherein corresponding reference characters indicate corresponding parts throughout the several views of the drawings and wherein: 
     FIG. 1 is a side elevational view of a prior art underwater vehicle having counter-rotating propellers; 
     FIG. 2 is a diagrammatic illustration of a prior art propulsion assembly; 
     FIG. 3 is a diagrammatic view, partly in section and partly in elevation, of one form of propulsion assembly illustrative of an embodiment of the invention; 
     FIG. 4 is an end view of the assembly of FIG. 3; 
     FIG. 5 is a perspective and partly sectional view of the assembly of FIGS. 3 and 4; and 
     FIG. 6 is a diagrammatic illustration, in section, of an alternative embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 3-5, it will be seen that an illustrative embodiment of the invention includes a drive shaft  30  rotatable by a drive source  20  (FIG.  2 ). The drive shaft  30  extends into a rigid cage  32  which includes fore-and-aft struts  34  and athwartships struts  36 . Water readily flows through the cage  32 . 
     Fixed to the drive shaft  30  is a first propeller  40  including a first propeller hub  42  to which are fixed propeller blades  44 . The outboard tips of the propeller blades  44  are fixed to a first ring  46  having thereon an annular array of gear teeth  48 . 
     Rotatably mounted on opposed struts  34  are spindles  50 ,  52  having fixed thereon bevel gears  54 ,  56 , respectively. The bevel gears  54 ,  56  are each provided with a single array of gear teeth  58 , which are complementary to, and engaged with, the first propeller gear teeth  48 . 
     A shaft  60  is rotatably mounted in the first propeller hub  42  and in athwartships struts  36 . Fixed to the shaft  60  is a second propeller  62  including a second propeller hub  64  to which are fixed propeller blades  66 . The outboard tips of the propeller blades  66  are fixed to a second ring  68  having thereon an annular array of gear teeth  70 . The gear teeth  70  are complementary to, and engaged with, the bevel gear teeth  58 . 
     Referring to FIG. 5, it will be seen that rotation of the drive shaft  30  in a first direction F causes rotation of the first propeller  40  in the same direction. Rotative movement of the first propeller gear teeth  48  induces rotation of the bevel gears  54 ,  56  with which the gear teeth  48  are meshed. Rotation of the bevel gears  54 ,  56 , meshed also with the gear teeth  70  of the second propeller  62 , causes rotation of the second propeller and shaft  60  in a second direction S opposite to the first direction F. 
     Thus, the single drive shaft  30  imparts counter rotational movement to the two propellers  40 ,  62 . 
     Referring to FIG. 6, it will be seen that in an alternative embodiment, the gear teeth  48  of the first propeller  40  are disposed on the first propeller hub  42 . The cage  32  includes an aft athwartships strut  36  comprising a support structure  74  from which extends a stationary central rod  72  in which the bevel gear spindles  50 ,  52  are rotatably mounted. The bevel gears  54 ,  56  are fixed on the outboard ends of the spindles  50 ,  52 , respectively. The bevel gear single arrays of teeth  58  are complementary to, and engaged with, the first propeller gear teeth  48 . The second propeller hub  64  is rotatably mounted on the rod  72  and the gear teeth  70  thereof are meshed with the gear teeth  58  of bevel gears  54 ,  56 . 
     In operation, the rotational movement of the first propeller  40  is transmitted, through the bevel gears  54 ,  56 , to the second propeller  62  which turns in a direction opposite, or counter, to the direction in which the first propeller  40  turns. 
     Thus, as in the above-described first embodiment, the alternative embodiment features a single drive shaft  30  for imparting counter rotational movement to two propellers  40 , 62 . 
     It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principles and scope of the invention as expressed in the appended claims.