Marine propulsion – Electric drive for propelling means
Patent
1995-09-20
1997-02-04
Avila, Stephen
Marine propulsion
Electric drive for propelling means
440 81, B60L 1102
Patent
active
055992153
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a propeller drive system for a vessel or the like, which system comprises first propeller are disposed, rotor and a second propeller are disposed, whereby the first and second electric motor are arranged in succession and the shaft of the first motor runs coaxially through the rotor of the second motor and through the associated hollow shaft, the first and second propeller being arranged in succession, second motor, respectively, and through them the first and second electric motor to rotate the motors either in the same direction or in opposite directions.
As is known, instead of using one conventional propeller, by using two propellers arranged in succession to rotate around the same central shaft in opposite directions, the operating efficiency of the propeller can be considerably improved. By using such a double propeller it is possible to achieve savings of about 10-20% in the fuel costs for the ship. The prime movers used in the prior art double propeller drive systems are conventional ship prime movers, which are designed to rotate only one shaft. However, a gear, typically a planetary gear, has been disposed near the propeller inside the hull of the ship, and this gear distributes the power on two coaxial, contra-rotating shafts. The planetary gear also functions as a speed reducer which makes the rotational speed of the prime mover suitable for the propellers. Consequently, the directions of rotation and the rotational speeds between the propellers are determined by the settings of the planetary gear, and they cannot be changed during operation. Furthermore, one problem with such a propeller drive system is the fact that if the prime mover or gear is damaged, the consequence is often a situation in which neither of the propellers can be used any more.
A propeller drive system like the one described above in the introductory paragraph for a vessel or the like for operating two contra-rotating propellers disposed in succession on two coaxial shafts is known from German Offenlegungsschrift 19 32 929. In that system the rotational speed of the motors is controlled partly by changing the rotational speed of the generators functioning as power supplies for the drive system by adjusting the rotational speed of the diesel engines rotating the generators and partly by means of a speed controller. Diesel drive enables adjustment of the rotational speed in the range of 100% to 30%. In this situation, when the rotational speed of the diesel engine is at the lowest, it is possible to adjust the rotational speed of the second motor by means of the speed controller down to zero and also make it rotate in the same direction as the second propeller. In this prior art arrangement, a prerequisite for speed adjustment is that the power supply of the motors is a combination of a diesel engine and a generator. In addition, the range of rotational speed variation is not quite sufficient and does not enable independent running and speed adjustment of the motors, which can be regarded as the most essential shortcoming of the solution in question. With regard to the operational safety of ships, it would be most desirable that each motor could be used independently.
The object of the present invention is to provide a propeller drive system whereby the propellers of a double propeller can be used substantially independently of each other in such a way that they can be given the desired direction of rotation and rotational speed entirely independently of each other. This also enables a situation in which either of the propellers can be used alone.
A propeller drive system in accordance with the invention, by which the above mentioned object is achieved, is characterized in that the first and second power supply comprise a first and second frequency converter, and that the control unit comprises means for controlling the frequency converters so that the direction of rotation of the motors and their rotational speed from zero up to the nominal speed can be chosen freely.
In the system in accorda
REFERENCES:
patent: 5078628 (1992-01-01), Garis
Derwent Abstract B7354X/08, Abstract of SU-A-469199, dated Apr. 30, 1975.
Derwent Abstract 93-034757/04, Abstract of SU-A1-1717478, dated Mar. 7, 1992.
ABB Industry OY
Avila Stephen
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