Ship propulsion with a gondola-like synchronous motor

Marine propulsion – Electric drive for propelling means

Reexamination Certificate

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Reexamination Certificate

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06231407

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to ship propulsion and may be applied in the design of a synchronous motor which is located in a hydrodynamically designed part of a housing arranged on the bottom of the ship's hull for the purpose of directly driving a propeller.
BACKGROUND INFORMATION
In conventional ship propulsion, described in U.S. Pat. No. 2,714,866, a motor is provided which is a three-phase alternating current motor with a squirrel-cage rotor, with the rotor sitting on a hollow shaft which is in turn linked to the drive shaft running inside the hollow shaft by a coupling. The drive shaft is coupled directly to the propeller. In this ship propulsion system, the stator of the motor is surrounded by a tubular housing which is in turn inserted into a pipe hanger-type housing part mounted gondola fashion on the bottom of the hull. The motor including the rotor bearings is cooled with fresh water pumped from a tank arranged in the hull into the interior of the motor housing and circulated throughout. (see, e.g., U.S. Pat. No. 2,714,866).
German Patent No. 917 475 describes a ship propulsion of a silimilar design, the stator of the three-phase motor is fitted into the hydrodynamically designed housing part in a form-fitting manner to cool it by water flowing past this housing part. The interior of the housing part accommodating the three-phase motor is filled with water under pressure. This water is provided for bearing lubrication and heat transfer.
In another convention ship propulsion described in U.S. Pat. No. 5,403,216 and a publication “A New Generation of Standard Diesel Electic RoRo Ferry” by Kvaerner Masa Yard, which may be designed for a drive power of 10 MW or more, the dynamoelectric motor is supported with its stator on radially arranged web plates in the surrounding housing; the web plates used in this manner serve at the same time to form cooling channels for a gaseous coolant supplied from the marine hull. A synchronous motor with a squirrel-cage rotor is usually used as the motor, with the rotor optionally cooled by its arrangement on the hollow drive shaft through which water flows. With such a propulsion device, the ratio between the maximum diameter of the drive housing and the propeller diameter are selected so that the ratio between the two is less than 0.65, preferably in the range between 0.4 and 0.5. It should be recalled here that the propeller diameter cannot be selected of any desired size. The above-mentioned ratio of outside diameters influences the propulsion efficiency, which is inversely proportional to, the above-mentioned diameter ratio.
To cool an electric motor operated underwater, it is also known that insulation oil used as coolant can be pumped in circulation so that it releases heat to the surrounding water in cooling channels running axially in the area of the housing wall (U.S. Pat. No. 2,862,122 A). It is also known that high power (1 to 2 MW) three-phase motors set up outdoors can be cooled by passing a stream of air produced by a fan along the wall of the housing (German journal Siemens-Z. 1966, no. 40, page 13 ff.).
SUMMARY
An object of the present invention is to provide a system propulsion system with a drive power in the MW range while guaranteeing a favorable propulsion efficiency.
This object is achieved according to the present invention by the fact that three-phase motor is a synchronous motor and has a drive power of at least 2 MW, the rotor of the synchronous motor is a permanent-magnet rotor, and the interior of the housing parts accommodating the synchronous motor is free of flowing coolant.
With such a design of the propulsion device, no additional cooling measures need to be taken to cool the drive motor because of the use of a synchronous motor with a permanent-magnet rotor that produces practically no heat losses due to current. In addition, since a permanent-magnet rotor is smaller radially than a squirrel-cage rotor, the radial space required by the drive motor is reduced. This leads to a more advantageous ratio between the outside diameter of the drive housing and the outside diameter of the propeller, so that the propulsion system has an excellent propulsion efficiency for a ship propulsion of this magnitude. In particular, when taking the measures according to the present invention, it is possible to design ship propulsions where the ratio of the outside diameter of the hydrodynamically designed housing part to the outside diameter of the propeller is less than or at most equal to 0.4.
Permanent-magnet rotors may be used instead of squirrel cage rotors or rotors separately energized via collector rings with synchronous motors, in particular for electric machines with drive powers up to about 30 kW (see, e.g., Siemens-Z. 1975, no. 49, pp. 368-374). Such motors with drive powers of about 2 to 5 MW have already been designed for submarine propeller drives, with the axially very short motor, which is thus relatively large with respect to its outside diameter, being arranged inside the hull. With this motor the pole shoes of the rotor are composed of several permanent magnets made of a special samarium-cobalt alloy and are glued to the pole shaft. The stator core assembly of this motor is surrounded by two cooling rings through which fresh water flows. The fresh water is recooled by seawater in heat exchangers (see, e.g., brochure PERMASYN-Motoren für U-Boot-Propellerantriebe by Siemens A G, order No. E 10 001-A930-A29, and “Yearbook of the Shipbuilding Society”, 1987, pp. 221-227).
If a ship propulsion designed according to the present invention is used in the upper power range (more than 5 to 10 MW), effective cooling of the winding overhang is important. It may then be expedient to provide an additional cooling device for each winding overhang of the stator. These additional cooling devices may be arranged in the interior space, which is present anyway due to the motor design, without any particular additional expense. Either fans arranged on the rotor shaft inside the winding overhang or a ring with a tubular cross section for each winding head at the end, this ring being provided with spray holes and its interior being connected by a pump to an insulating oil sump below the rotor shaft, may be used as cooling devices. In both variants, heat is removed from the coolant, whether air or insulating oil, in the same way as heat is removed from the stator via the surrounding motor housing wall.


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H. Bönning et al., “Der MEP-Motor, ein permanenterregter Fahrmotor für den Schiffsbetrieb,” 1988, pp. 229-234.
K. Magens, “Permasyn—Ein permanenterregter Synchronmotor für den schiffsbetrieb,” 1988, pp. 221-227.
H. Weh, “Die Transversalflussmaschine,” 1992, pp. 68-73.
J. Heinemann, “Elektrischer Motorpropeller—Stand der Entwicklung und Anwendung,” 1992, pp. 88-94.
DiBenito Bragone, “Il piú grande motore a magneti permanenti per propulsione navale”, Technologie& Transporti Mare, Feb. 1996, pp. 30-31. (English abstract provided).
“Manoeuvrability -A Unique Electric Thrust Unit”, Marine Propulsion, Sep./Oct/ 1989, p.24.
Mikko Niini, “A new generation of ‘standard’diesel-electric RoRo ferry”,RoRo94, Session 10, Gothenburg (Apr. 27, 1994).

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