Electricity: motive power systems – Plural – diverse or diversely controlled electric motors – Running-speed control
Patent
1997-06-27
1999-04-20
Ro, Bentsu
Electricity: motive power systems
Plural, diverse or diversely controlled electric motors
Running-speed control
318 53, 440 6, 440 79, B63H 2117, B63H 2122
Patent
active
058960163
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method for optimizing the efficiency of bow and stern screws in ships--particularly ferries--where the rotational speed of the front screw (i.e. bow screw) is in each case less than the rotational speed of the rear screw (i.e. stern screw). In addition, the invention also relates to the associated arrangement for adjusting the rotation speed of the bow screw in those ships having a symmetrical screw arrangement and respectively associated separate drives.
Modern ferries may have a bow screw and a stern screw, which are each driven by separate drives. Such an arrangement avoids having to turn the ship in order to reverse its direction of motion. Such ships with a symmetrical screw arrangement are normally operated with a symmetrical screw arrangement in accordance with an empirically derived characteristic. In particular, this means that the front screw is driven at a rotational speed which is about 10% lower than the rotational speed of the rear screw, depending on the direction of travel, in order as far as possible to avoid in particular any braking effect from the front screw, which cannot be used for thrust.
As is known, the braking effect increases the power consumption of the entire vessel system. A multiplicity of factors which cannot be measured, but which nevertheless influence the optimum rotation speed of the front screw, cannot be taken into account where one merely relies upon previous empirical solutions. Hence, the known procedure remains unsatisfactory in many respects. The efficiency of the entire drive system is, under some circumstances, poor, since changing flow conditions, wave motion and similar external factors are not detected exactly.
SUMMARY OF THE INVENTION
An object of the invention is to provide an improved method and apparatus for the adjustment of the rotational speed of the bow screw to a value which leads to a more favorable overall level of drive power consumption at any ship speed and for any other influencing factors.
The object is achieved via a method in which the minimum-value regulation of the sum of the recorded real power levels of both drive systems is carried out for efficiency optimization. The associated arrangement for adjusting the rotational speed of the bow screw is characterized by a regulator using the real power levels of both drives as input variables, that rotational speed of the bow screw at which the sum of the real power levels is a minimum being determined in the regulator.
This method can be used to supplement initial control using empirical values, and provide a correction to these values. Optimization can also take place even during the running-up process of the stern screw. In the so-called split mode, that is to say when moving slowly in a harbor basin or the like, the helmsman is nevertheless given complete freedom to use both drives independently.
It is advantageous in the case of the invention that it is no longer absolutely essential to determine and implement empirical characteristics in advance, and that movement nevertheless takes place with a minimized total power. Since the drive power levels in ferries are normally in the MW range, a not inconsiderable energy saving may be expected overall.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of this inventory reference should now be made to the embodiment illustrated in the FIGURE, which shows a schematic block diagram of a system providing such minimum-value regulation in ferries.
DETAILED DESCRIPTION
In the FIGURE, 1 indicates a ferry which has a complete drive system both at the bow and at the stern, which drive systems are of identical construction. In consequence, while traveling, such ships are able to reverse the direction of travel without any turning maneuver. In detail, the figure shows a first engine 2, with the associated screw 3, and a second engine 4 with the associated screw 5. Both engines 2 and 4 are driven via suitable power control elements 6 and 7, which are connected to the ship powe
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patent: 4836809 (1989-06-01), Pelligrino
patent: 5009621 (1991-04-01), Bankstahl et al.
patent: 5441388 (1995-08-01), Berger
Ship & Boat International, May 1983, p. 11, "Rudder Propellers For Road Ferry Propulsion".
Reinhold Knecht, "Die Schottel-Masterpilot-Steuerung", HANSA-Schiffahrt-Schiffbau-Hafen, 1986, No. 22/23, pp. 1819-1822.
Marine Propulsion, May/Jun. 1988, p. 35, "A.c. Thruster Drives For Pipelayer".
Schiff & Hafen/Seewirtschaft, Jul. 1990, p. 84, "ETA-Pilot Now Marked By SSPA".
Van Obering H. Heuser, "Linienentwurf und Modelluntersuchung von Groben, Schnellen Binnenfrachtschiffen Geringer Volligkeit", Schiff & Hafen, Jan. 1965, No. 17, pp. 10-13.
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Ro Bentsu
Siemens AG
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