Marine propulsion – Means to control the supply of energy responsive to a sensed...
Reexamination Certificate
2002-06-10
2003-12-09
Avila, Stephen (Department: 3617)
Marine propulsion
Means to control the supply of energy responsive to a sensed...
C440S002000, C440S006000
Reexamination Certificate
active
06659815
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to watercraft and more specifically to control systems and motors for watercraft that use electric motors and/or electric control systems.
BACKGROUND OF THE INVENTION
Electric boats once dominated the power watercraft field but became disfavored due to the lower power to weight ratio and lower speed available in electric boats compared to fossil burning watercraft that later developed. Public interest in electric watercraft has resurfaced recently due to their advantages of lower pollution, lower noise, and in some cases elegance, compared with air breathing fossil fueled watercraft. Because of their use of low energy density power supplies such as lead acid batteries, metal hydride batteries, and in the future, fuel cells (including the chemical energy conversion unit) and the like however, electric boats have limited range and speed compared to equivalent sized fossil boats. Accordingly, any improvement in propulsion efficiency of an electric boat would directly ameliorate this problem and improve acceptance of electric boats by the public.
Much electric boat motor and battery technology arose from advances in the electric golf cart and electric car industries. Accordingly, most commercial motors used in electric boats have been designed for those other uses. Many of those active in the electric boat industry use series wound motors and believe that the torque versus speed characteristics of this motor are well optimized for electric boating because the motor speed automatically increases to reach a suitable maximum propeller resistance (Paul Kydd,
Electric Boat Journal
Issue 4, Vol. 6). On the other hand, electronic technologies designed for golf carts, cars and trolleys, such as electrified rails that provide electric power, satellite/roadway navigational aids, automated braking systems, back up radar monitor systems and the like have limited or no use in electric boats. Thus, the electric boat industry cannot rely on aftermarket parts and solutions from these other industries but must invest in and exploit new technologies that solve the particular problems of electric boats.
Improved batteries and motors are the automotive technology advances that seems to relate most to electric boating. Recent developments in permanent magnet direct current motors that utilize high powered rare earth magnets, as exemplified by the Lynch motor taught in U.S. Pat. No. 4,823,039 are greatly welcomed. Such motors are expected to bring great improvements to the industry. However, most motors still are limited to having optimum performance peaks at a narrow or limited range of speed and load. Moreover, even the best motors, which utilize rare earth element high powered permanent magnets generally have low efficiencies at low speed.
A review of advances in the electric motor field would not be complete without acknowledging the improvements made by David Tether, including, among other things, permanent magnet motors having planetary/sun gear arrangements that provide significant advantages for regeneration and for use in watercraft, especially sailboats, as represented in U.S. Pat. Nos. 5,575,730, 5,067,932, 5,851,162 and 5,863,228. Also, the “ecycle” motor (see www.ecycle.com) promoted and refined by Daniel J. Sodomsky, which has many desirable attributes, with high performance magnets in the rotor and generally high performance overall. These motors alleviate many problems but still, like other motors before them, generally have highest efficiency at a high rotational speed. Thus, a general problem with applying electric motors in watercraft is that motor efficiency drops off at low speed and propulsion efficiency drops off at high speed. The relative lack of discussion of these phenomenon reflects the fact that most motors designers take the problems for granted. It should be noted in this context that shunt wound motors sold in watercraft from the Electric Launch Company of Highlands, New York seem to be controlled by a circuit that independently drives the two coils. However, details of the algorithm used have been kept from the public and the control circuit is sold in a permanent opaque block of epoxy, and details of the circuit appear not to have been published.
Another problem in the watercraft industry that appears to have been overlooked generally in the electric boat field is the need to match propeller slip with boat output at different watercraft velocities. Typically, a fixed propeller of a watercraft is chosen based on optimum performance of a given motor and boat at high speed or at low speed, or a compromise between the two speeds. During use, the operator merely increases power to the motor without regard to propeller slippage until the watercraft reaches a desired speed. This strategy may suit the operation of boats that have a maximum speed of only a few knots and may be appropriate for fossil burning watercraft in an era of very cheap energy. However, high speed personal watercraft, particularly heavy ones that can travel fast may require time to reach high speeds, and excessive propeller slip becomes more of a problem that noticeably affects efficiency of battery use, fuel cell power use and hydrocarbon combustion use in fossil fueled watercraft. Furthermore, the very high propeller slippage condition of cavitation becomes greater as higher revving motors are used to achieve higher speeds. These problems generally have remained unrecognized because the commercial electric boat industry (in particular, pleasure craft less than 35 feet long) focuses on slow boats limited to their displacement hull speeds.
Yet another problem with many electric motors used for watercraft is the mechanism used for removing excess heat. In many terrestrial applications an electric motor is air cooled. In boats, however, the moist and often salty marine environment is inhospitable to many materials used. Special materials and finishes may be required. A particular problem in this regard is when the entire motor is sealed. Trolling motors have been designed that rely on transfer of heat from an exterior case that surrounds the motor, with water. Such motors are generally thought as not very reliable for long term use. In some cases, an enclosed motor case cannot completely contact water, and heat build up is a greater concern. An example of the latter is the motor configuration used by Maruta Electric Boatworks LLC, (www.aquaskate.com) wherein an electric motor is completely enclosed within a sealed hull. As trolling motors become more widely used for a variety of new boat hull designs that limit contact of water with the motor case, removal of heat will become more of a problem. Use of a separate pump with its own electrical circuit and pipes adds an extra level of complexity which undesirably increases costs and presents further opportunity for breakdown. A passive system or simpler system would advance this art.
Yet another problem is that control systems such as auto pilots have been developed primarily for complex operation in larger vessels, where high cost systems have been first adopted and operators are accustomed to training. Simple one button or twist knob analog operation of simple controls such as auto heading is desired by many pleasure boaters who may not want to read an operation manual before using a control.
In sum, boats are very sensitive to propulsion efficiency but most of the motors and their control systems for electric boats have been developed for the automobile and golf industries. Further, present commercial electric pleasure craft are designed primarily for low speed operation and manufacturers have not seriously challenged the limits of motor performance. Any motor or control system that improves the overall efficiency and convenience of pushing a boat would yield rich dividends in extending the performance of the power supply and in gaining further public acceptance of products from this industry, particularly for electric motor powered pleasure watercraft less than 45 feet long.
SUMMARY OF THE INVENTION
Avila Stephen
Maruta Electric Boatworks LLC
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