Title:
MARINE PROPULSION DEVICE
Kind Code:
A1


Abstract:
A marine propulsion device such as an outboard motor includes a submersible electric motor having a propeller connected directly with the drive shaft of the motor. The motor is an efficient brushless motor having symmetrical elliptical coils connected with a stator which generate magnetic flux when current is passed through the coils to rotate a rotor for driving the drive shaft. The motor is arranged in a housing having a nozzle connected with a rear portion thereof which surrounds the propeller to reduce cavitation. Cooling fins are provided on the outer surface of the housing to assist with cooling the motor and a motor controller arranged in the housing.



Inventors:
Scott, Sean (Crownsville, MD, US)
Application Number:
12/123661
Publication Date:
11/27/2008
Filing Date:
05/20/2008
Primary Class:
Other Classes:
440/53, 440/67, 440/84, 114/162
International Classes:
B63H21/17; B63H1/18; B63H20/08; B63H21/21; B63H25/06
View Patent Images:
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Primary Examiner:
SWINEHART, EDWIN L
Attorney, Agent or Firm:
SEAN SCOTT (ANNAPOLIS, MD, US)
Claims:
What is claimed is:

1. A marine propulsion device, comprising (a) a submersible housing containing a brushless electric motor having a longitudinal drive shaft extending from said housing; and (b) a propeller connected with said drive shaft and being driven for rotation by said motor.

2. A marine propulsion device as defined in claim 1, wherein said motor includes (a) a cylindrical stator having a longitudinal axis and defining a chamber; (b) a rotor arranged within said stator chamber coaxial with said stator, said drive shaft being connected with said rotor; (c) a plurality of magnets connected with an outer surface of said rotor; and (d) a plurality of symmetrical coils connected with an inner surface of said stator, each of said coils comprising a conductor wound in an elliptical configuration, a long axis of each coil being parallel with the stator longitudinal axis, whereby when current is supplied to said coils, said coils produce a magnetic flux which acts on said magnets to cause said rotor to rotate with respect to said stator.

3. A marine propulsion device as defined in claim 2, wherein said housing includes a nozzle extending rearwardly therefrom, said propeller being arranged within said nozzle, whereby said nozzle reduces cavitation resulting from rotation of said propeller.

4. A marine propulsion device as defined in claim 3, wherein said nozzle has a truncated conical configuration.

5. A marine propulsion device as defined in claim 3, wherein said housing includes a plurality of longitudinal cooling fins arranged in spaced relation about the housing exterior surface.

6. A marine propulsion device as defined in claim 5, and further comprising a controller arranged within said housing and connected with said motor.

7. A marine propulsion device as defined in claim 2, and further comprising means for connecting said housing with a vessel.

8. A marine propulsion device as defined in claim 7, wherein said connecting means comprises a bracket connected with a vessel transom and a shaft connected between said bracket and said housing.

9. A marine propulsion device as defined in claim 8, and further comprising a rudder connected with said shaft adjacent to said housing.

10. A marine propulsion device as defined in claim 9, and further comprising a control system connected with said bracket.

11. A marine propulsion device as defined in claim 10, wherein said control system includes means for rotating said shaft relative to said bracket to steer the vessel and means for supplying electric current to said motor.

Description:

BACKGROUND OF THE INVENTION

The present invention relates to a marine propulsion system in the form of an outboard motor. Such motors have been used for many years to propel small vessels on protected bodies of water. The most common types of outboard motors are gas and electric. Internal combustion engines which rely on gas for fuel provide greater horsepower. However, they are noisy and contribute to pollution of the body of water on which the vessel is used. Accordingly, many bodies of water restrict the size of the gas powered motors allowed or eliminate them altogether.

Electric outboard motors are much cleaner and quieter than gas powered motors. They are particularly useful for propelling rowboats and fishing boats to maneuver the boats in shallow water and around submerged obstacles such as fallen trees. The main drawbacks with electric outboard motors are the limitation in horsepower, the amount of current required to operate them, and the heat generated by the motor.

The present invention was developed in order to overcome these and other drawbacks of prior electric outboard motors by providing a submersible motor of greater efficiency with increased output torque.

SUMMARY OF THE INVENTION

The marine propulsion system according to the invention includes a submersible housing containing a brushless electric motor having a longitudinal drive shaft extending from the housing. An external propeller is connected directly to the drive shaft for rotation by the motor. Preferably, the motor produces a high torque output with reduced energy consumption. It includes a cylindrical stator having a longitudinal axis and defining a chamber in which a rotor is coaxially arranged. The drive shaft is connected with the rotor. A plurality of magnets are connected with the outer surface of the rotor and a plurality of symmetrical coils are connected with the inner surface of the stator. The coils are formed by winding a conductor in an elliptical configuration with the long axis of each coil being parallel with the longitudinal axis of the stator. When current is supplied to the conductors of each coil, the coils produce a magnetic flux which acts on the magnets to cause the rotor to rotate which in turn drives the propeller.

The housing includes a nozzle which extends from the rear and surrounds the propeller to reduce cavitation. In addition, the housing includes a plurality of longitudinal cooling fins arranged in spaced relation about the housing exterior surface to assist with dissipating heat generated in the housing by the motor.

A bracket is provided to connect the marine propulsion system to the transom of a vessel and a shaft is connected between the bracket and the motor. The shaft includes a rudder adjacent to the housing to assist with steering the vessel by pivotal movement of the shaft and housing. A controller for the motor is arranged within the housing and a control panel is connected with the bracket for use by the operator to control the speed and direction of the motor and the orientation of the shaft.

BRIEF DESCRIPTION OF THE FIGURES

Other objects and advantages of the invention will become apparent from a study of the following specification when viewed in the light of the accompanying drawing, in which:

FIG. 1 is a sectional side view of the marine propulsion system according to the invention;

FIG. 2 is a front plan view of the system of FIG. 1;

FIG. 3 is a rear perspective view of the system of FIG. 1;

FIG. 4 is a side plan view of the housing of the marine propulsion system according to the invention;

FIG. 5 is a partial sectional view of the electric motor of the marine propulsion system according to the invention; and

FIG. 6 is a top plan horizontal sectional view of the motor taken along line 6-6 of FIG. 5.

DETAILED DESCRIPTION

The marine propulsion system according to the invention will first be described with reference to FIGS. 1-3. As shown therein, the system includes a control assembly 2, a bracket 4 for mounting the system to a vessel such as the transom of a boat, a shaft 6 connected with the mounting bracket, and a submersible housing 8. Within the housing is mounted a brushless electric motor 10 and a variable voltage controller 12 for the motor. The motor has a drive shaft 14 which extends from the housing along a longitudinal axis thereof, and a propeller 16 is connected directly with the drive shaft. No transfer linkage is required between the motor and the propeller.

The housing has a curved nose portion 18 at the forward end in the direction of travel so that the housing passes smoothly through the water and sheds debris. Rearwardly, the housing includes a nozzle 20 which preferably has a truncated conical configuration and surrounds the propeller as shown in FIGS. 1 and 3. The nozzle reduces cavitation produced by the propeller as it rotates in the water, thereby increasing the thrust of the motor. A plurality of arms 22 arcuately spaced about the nozzle connect it with the housing.

The housing is formed of any durable water proof material such as metal or synthetic plastic and is shown in detail in FIG. 4. On the exterior surface of the housing are provided a plurality of longitudinal cooling fins 24 which serve to dissipate heat generated by the motor within the housing to the water in which the housing is submerged.

The motor 10 is a brushless electric motor. Referring now to FIGS. 5 and 6, the motor will be described in greater detail. It includes a cylindrical stator 26 having a longitudinal axis and defining a chamber in which a cylindrical rotor 28 is arranged. The stator includes a plurality of symmetrical windings or coils 30 on the inner surface thereof as will be developed below, and the rotor includes a plurality of magnets 32 connected with the outer surface thereof, preferably in contiguous relation. The drive shaft 14 is connected with the central portion of the rotor. The rotor and shaft are coaxial with the stator. The magnets are connected with the rotor in a conventional manner. Preferably, the magnets are polarized permanent magnets and the polarity of each successive magnet is reversed around the circumference of the rotor. Thus, each magnet produces a magnetic field which are alternately reversed about the rotor.

Each coil is formed of a conductor 34 wound with a jig into an elliptical configuration. The conductor is preferably formed of copper and preferably has a rectangular cross-sectional configuration. The conductor is wound so that the flat portion of the conductor is contiguous. The wound coils are pressed into an annular configuration to fit within the stator 26 with which each coil is connected in a conventional manner. The ends of the conductors of each winding are connected with a current supply so that as current runs through each coil, magnetic flux is generated. The symmetrical coils increase the efficiency of the motor by allowing more copper to be present in each coil. The greater copper density and symmetrical shape of the coils increase the magnetic flux generated by the coils. The coils are operated pairs to produce magnetic fluxes of different direction. The interaction of the magnetic flux from the coils and the magnetic fields from the permanent magnets on the rotor causes the rotor to rotate about its axis, thereby rotating the shaft 14.

The solid rectangular shaped conductor increases the density of the coils and thus increases the amount of conductive material in the space provided for the coils. The additional density allows the radial axis of the motor to be reduced and improves the overall efficiency of the design. The torque is increased and the motor diameter is reduced. The reduction in diameter also increases the heat transferability and thus increases the longevity of the magnets and reduces wear on the motor.

Referring once again to FIGS. 1 and 2, power for the motor can originate from an external battery or from a generator driven by a separate motor. A cable (not shown) extends from the upper control assembly 2 through the shaft 6 to the interior of the housing where it is connected with the coils of the motor. In addition, control signals from the control assembly are delivered to the controller 12 via the cable. This allows the motor to be driven in forward and reverse directions and allows the speed of the motor to be adjusted by adjusting the current supplied to the motor. The variable voltage controller can accept any voltage between 24 and 72 VDC and greatly increases the applicability of the system by allowing the custom configuration of the power source based on cost, size and weight.

The control panel can be operated manually in a conventional manner or via a remote control cable 34. In the exemplary embodiment shown in FIGS. 1 and 2, power cables 36 are connected with the control panel. A steering cable may be connected with the base 38 of the control panel to pivot the shaft relative to the mounting bracket and steer the vessel in a conventional manner. In lieu of steering cables, an articulated arm (not shown) may be connected with the control panel for manual steering. To further assist with steering, a rudder 40 is connected with the shaft 6 above the housing. In addition, a grounding skeg 42 is connected with the bottom of the housing.

The marine propulsion system according to the invention has minimal impact on the environment because it produces no exhaust and minimal noise. Moreover, because the motor is submersed in the water adjacent to the propeller, any noise or heat generated by the motor is dispersed in the water. The heat dissipation from the motor and controller increases the efficiency and longevity of these components.

While the preferred forms and embodiments of the invention have been illustrated and described, it will be apparent to those of ordinary skill in the art that various changes and modifications may be made without deviating from the inventive concepts set forth above.