Electric marine propulsion system
First Claim
1. A marine propulsion system comprising:
- a diesel engine for providing a continuous rotational shaft horsepower, said diesel engine operated at a speed of maximum efficiency;
an alternator having a standard rated frequency output for a standard rated input RPM connected to be driven by said diesel engine, said alternator standard rated RPM selected to be less than said generated diesel engine continuous shaft RPM whereby voltage is generated having a higher frequency than said rated standard frequency and said diesel engine and alternator produces a power output at a maximum efficiency;
a frequency converter connected to receive voltage from said alternator, said frequency converter providing an alternating output voltage having a selectable frequency;
an AC motor connected to receive a voltage from said frequency converter, said AC motor producing a horsepower output which is constant and a torque proportional to the frequency of said received voltage; and
gear reduction means for coupling said AC motor and a propeller shaft, whereby said propeller shaft RPM is controlled by said frequency converter output voltage frequency, which may be varied by said frequency converter.
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Accused Products
Abstract
An AC marine propulsion system which provides a constant continuous rated horsepower availability at the standard rated engine RPM, over the full useful operating range of the propeller. A prime mover diesel engine is operated at its continuous rated speed to provide for maximum fuel efficiency. An alternator connected to the prime mover is driven at a speed which is higher than the standard rated alternator speed, thus producing higher than standard rated voltage and frequency. The combination of prime mover and alternator provides for an optimum system mass to power ratio. An AC motor is coupled through a gearbox to a fixed pitch propeller system. A frequency converter is dispsoed between the alternator and AC motor. Propeller RPM is controlled by changing the frequency of the voltage supplied to the AC motor. Variable shaft RPM at constant horsepower output is supplied to a fixed pitch propeller by selectively varying the frequency of the voltage supplied by the converter from 100% of maximum RPM to 40% of maximum RPM at 100% shaft horsepower.
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Citations
14 Claims
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1. A marine propulsion system comprising:
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a diesel engine for providing a continuous rotational shaft horsepower, said diesel engine operated at a speed of maximum efficiency; an alternator having a standard rated frequency output for a standard rated input RPM connected to be driven by said diesel engine, said alternator standard rated RPM selected to be less than said generated diesel engine continuous shaft RPM whereby voltage is generated having a higher frequency than said rated standard frequency and said diesel engine and alternator produces a power output at a maximum efficiency; a frequency converter connected to receive voltage from said alternator, said frequency converter providing an alternating output voltage having a selectable frequency; an AC motor connected to receive a voltage from said frequency converter, said AC motor producing a horsepower output which is constant and a torque proportional to the frequency of said received voltage; and gear reduction means for coupling said AC motor and a propeller shaft, whereby said propeller shaft RPM is controlled by said frequency converter output voltage frequency, which may be varied by said frequency converter. - View Dependent Claims (2, 3, 4, 5)
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6. A marine propulsion system for independently driving a pair of propeller shafts, comprising:
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first and second diesel engines, each of said diesel engines connected to drive first and second alternators, whereby a pair of diesel generator sets are provided, said diesel engines having a controlled shaft operating speed set to produce maximum shaft horsepower at maximum efficiency, said alternators selected to have a standard rated RPM for producing a standard rated output voltage frequency substantially less than said operating speed, whereby a maximum KW power generation efficiency is obtained at a voltage having a frequency higher than said standard rated output voltage frequency; a pair of frequency converters connected to each of said alternators for providing a variable frequency output voltage, said frequency being selected by an operator of said system to control the RPM of said propeller shafts; an AC motor connected to each of said alternators, said AC motors providing an output shaft RPM which varies along with torque in response to a varying input voltage frequency while maintaining output shaft horsepower constant; and
, a pair of reduction gear transmissions, each coulping a pair of said AC motor shafts to a respective propeller shaft, whereby each of said shafts is driven by a pair of motors at an RPM and torque controlled by selecting the voltage output frequency of said frequency converters. - View Dependent Claims (7, 8)
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9. In a marine propulsion system, a method for driving a solid cast propeller having a fixed pitch comprising:
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coupling an AC motor to said propeller, said AC motor providing a varying torque at varying RPM to said propeller in response to a varying input voltage frequency; supplying an AC voltage to said AC motor having a frequency for selecting said AC motor RPM; and controlling the frequency of said AC voltage whereby the RPM of said AC motor shaft and coupled propeller is controlled. - View Dependent Claims (10, 11, 12)
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13. A marine propulsion system for providing a variable drive to a constant pitch propeller comprising:
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a diesel engine driven alternator for providing alternating current, said diesel engine operated at a speed of a maximum efficiency, and said alternator producing a current having a frequency higher than its standard rated frequency of operation; a frequency converter connected to receive said alternator current having a frequency higher than a standard rated frequency of operation, said converter providing an output voltage at a frequency which is selectable; and an AC motor connected to receive said frequency converter output, and coupled to drive said propeller, said AC motor providing a variable rotational speed to said propeller proportional to a selected voltage frequency from said frequency converter, said AC propeller motor providing a constant horsepower for each selected frequency. - View Dependent Claims (14)
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Specification