A DRIVE SYSTEM FOR CONSUMERS ABOARD A SHIP

Abstract: In a drive system for several consumers, such as pump (11­ -13) aboard ships having a motor driving the ship's screw, said motor driving a hydraulic main pump (1) which is a low-speed piston or plunger pump with a large adjustable stroke volume, said pump (1) feeding hydromotors (17, 18, 19) which directly drive pumps (11-13) necessary for maintaining the main drive of the ship or otherwise associated with the main drive and/or said pump (1) providing such consumers directly with hydraulic fluid.

Description: Title: A drive system for consumers aboard a ship The present invention relates to a drive system for various consumers, such as pumps, aboard a ship, comprising a motor driving the screw, use being made of a motor-driven hydraulic pump which drives a hydromotor. A similar drive system is described in European patent application 009241 as an auxiliary drive system for the generator driven mainly by a steam turbine, said generator supplying electric power to the mains of a vessel. The consumers are driven by electric motors connected to said mains. An advantage of driving consumers aboard ships by means of electric motors is the great flexibility, for it is easy to tap the mains. Driving consumers electrically, however, has a number of drawbacks. In the case of failure in the mains voltage and hence drop-out of consumers fed by the mains, subsystems, necessary for maintaining the main drive, such as a gearbox, may be damaged when the lubricating oil pump drops out, while the screw shaft connected to the gearbox continues to rotate. Consequently, use is practically always made of some stand-by unit. Another drawback of electric motors is that they are designed for a substantially constant speed, so that they can hardly be controlled. The choice of the size of electric motors is therefore based on the worst circumstances imaginable, the largest couple imaginable, e.g. in the case of cold lubricating oil in a lubricating oil pump. These two aspects result in that practically always more power is fed to the consumers than is strictly necessary for their operation. Moreover, such over-dimensioned electric motors constantly operate at partial load. Also, in the case of conversion of mechanical power, e.g. of the screw shaft, into electric power, problems arise when the screw shaft speed varies strongly. In order to nevertheless obtain electric power of a fixed frequency, additional steps are required, such as the use of gearboxes with variable transmission, frequency changers or features for the screw drive, such as an adjustable screw by means of which the propulsion can be varied with constant screw shaft rotation. With electric motors rapid wear of bearings may occur if they are subjected to vibrations and in this respect they require relatively substantial maintenance. When they are used in a humid environment, the electric motors should be watertight. Particular features are also necessary when the electric motors are used in an environment subject to explosion hazard. The present invention is based on the insight that the above drawbacks of an electric drive system for consumers aboard a ship can be avoided and that the reliability of the main drive of the ship can be increased by driving at the least consumers associated with the main drive hydrostatically. Hydrostatic drives can be derived from the screw shaft. All consumers can remain operative as long as the screw shaft rotates. Also, much fewer additional provisions are required to take care of a possible failure. The hydromotors used in the case of a hydrostatic drive system, both as regards speed and couple, are simple to control and controllable over a large range, enabling to set the exactly required couple for the consumers. Hydromotors, moreover, can be connected directly to the hydraulic pumps by means of pressure lines. Besides, hydromotors and pumps can be attuned to each other excellently. Furthermore, a hydrostatic drive system is highly flexible, since any place is accessible by means of pressure lines. Speed variations in the drive of the main pump can be compensated for in a simple manner, and a hydraulic pump can be easily connected to the shaft of any machine, e.g. by means of a gearbox, even to the shaft of the propulsion motor. Finally, hydromotors and hydraulic pumps are already watertight by nature, so that no additional features are necessary for consumers operating in a humid environment. The use of hydromotors and hydraulic pumps in an environment subject to explosion hazard does not give problems therefore. A hydrostatic drive, in particular on board ships has therefore many advantages as compared to an electric drive system for consumers. A drawback of a hydrostatic drive system as main drive system for consumers is that hydraulic pumps have a high air-borne and structure-borne sound level. Air-borne sound level means the sound level measured at a given distance from the pump, whereas structure-borne sound level means the vibration level produced by the pump and passed on to lines of the system and to the pump foundation. Consequently, it is an object of the present invention to provide a hydrostatic drive system for consumers aboard a ship which minimizes the sound level, while maintaining all advantages thereof. To this effect, according to the present invention, the hydraulic pump in a drive system as defined above is a low-speed piston or plunger pump of large adjustable stroke volume and arranged to directly drive those consumers that are necessary for maintaining the main drive or that are otherwise associated with the main drive and/or directly supplies such consumers with hydraulic oil through adjusting means. Consumers eligible for such a drive system are e.g. lubricating oil pumps for the gearbox, for the motor, for the screw shaft bearings, the fuel suction pumps, for the screw adjusting mechanism and other controls of the ship's drive. A low-speed piston or plunger pump of adjustable stroke volume, when loaded, is practically noiseless and hardly produces vibrations. Due to the low air-borne and structure borne noise level, the pump can be mounted directly on a gearbox without requiring additional features. Moreover, this makes for a compact construction. When this pump is integrated in a hydraulic system, whith additional pressure control means, there is created a hydraulic network at constant pressure to which various consumers can be connected simultaneously. The hydraulic pump has a vital function in such a system, which imposes severe demands on the reliability and the life thereof. Due to the low speed and the specific construction of the pump, and partly due to the low load thereon, these requirements can be better met than by a high-speed pump. According to the present invention, for optimally obtaining these effects, the hydraulic pump of large adjustable stroke volume is used preferably at a speed lower than 1,000 rpm. At these low working speeds, wear is less and service life is extended. Preferably, a radial piston or plunger pump is chosen for the hydraulic pump. Such a pump, described in German Offenlegungsschrift 2,203,054, can be adjusted in a simple manner by varying the eccentricity. The requirements imposed on the hydraulic pump under the given circumstances have been found to be met best by a slow-speed radial piston or plunger pump with adjustable stroke volume and adjusting range to match. Such a hydromotor, i.e. one not designed as a pump, has been found to be excellently suitable for the object contemplated. Due to the hydrostatic bearing of the plunger-piston hose support, heavy impacts on the main bearing of the pump are damped. Moreover, vibrations produced by the piston are damped in this manner. When the hydraulic pump is used on board ships, it can be driven by the propeller shaft of the ship through transmission means. This coupling does not require damping means e.g. between the pump and a fixedly mounted gearbox. When the hydraulic pump is thus coupled to the propeller shaft, the pump is subjected to speed variations of the propeller shaft. To take up these speed variations in such a manner, that no appreciable interference is encountered by the consumers, a hydraulic pump is proposed within the scope of the present invention that has an adjustable stroke volume about twice the maximum difference in stroke volume over the speed variation range of the propeller shaft. Minor speed variations are not troublesome for that matter, since these variations can be taken up by the control means incorporated in the hydraulic circuit. On board ships having an adjustable screw, this adjustment possibility is used only seldom in general, the full adjusting capacity is only necessary during adjustment e.g. during manoeuvring or when the speed of the ship is changed. Most of the time, the installation needs only supply a limited power necessary to fix the screw in the desired position. Nevertheless, such an installation should be designed for a high power, i.e. for peak loads. According to the present invention, the drive system for the adjustable screw can be connected to the hydraulic pump so that at peak load sufficient power can be used for the screw adjustment and otherwise, this power can be used for charging the batteries incorporated in the system. Peak loads for adjusting the screw can then be taken up by discharging the batteries and/or by adjusting the hydraulic pump to a larger stroke volume, thus excluding interference with the other consumers. It is observed that British patent application 2,038,747 discloses per se to derive power from the main screw shaft drive motor for driving an auxiliary screw by means of a hydraulic pump and a hydromotor. Partly due to the fact that the hydraulic pump in this publication is mentioned as an equivalent alternative for an electric generator for supplying the driving power for an auxiliary screw, it is not possible to derive from that publication the inventive idea to drive consumers necessary for the maintenance of the main drive of a ship by means of hydromotors fed by a low-speed piston or plunger pump driven itself by the main motor. One embodiment of the drive system according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a block diagram of a hydrostatic drive system; and Fig. 2 is a cross section of a radial piston motor functioning as a hydraulic pump. The block diagram of Fig. 1 shows a shaft-driven main pump 1 driven e.g. by means of a gearbox 16 from a screw shaft of the ship. Preferably, a radial piston pump as shown in Fig. 2 is used for the pump. The main pump is connected through pressure lines 8 to a battery 3 having a distributing reducing block. The adjusting unit 10 of the adjustable screw is fed directly by pressure line 8. Moreover, hydromotors 17, 18, 19 driving the pumps 11, 12 and 13, respectively, are connected to pressure line 8. Return lines extend from said hydromotors to the return line 14 of the main pump 1. Between pressure line 8 and return line 14 there is provided a further hydromotor 4, in the present case driving a scavenging pump 5, which draws in pressure fluid from a reservoir 15. This pressure fluid, prior to being supplied to the return line, is passed through a filter 7. The line system taps on the other hand pressure fluid by means of cooler 6 in the reservoir 16. To provide for cases in which the main pump is not operative, e.g. when the screw shaft is stationary, the system is fitted with a stand-by pump 2, driven electrically. Fig. 2 shows an embodiment of a radial piston motor adapted to function as a hydraulic pump 1. This low-speed radial piston motor with adjustable stroke volume and with pistons 28 centrally supported on a shaft 30 is not designed as a pump, it is true, but has been found to be excellently suitable for this purpose, in particular within the scope of the hydrostatic drive system for consumers aboard a ship according to the present invention The stroke volume can be adjusted in a simple manner by means of an eccentric ring 22, which can be adjusted and fixed by means of oil pressure control in chambers 28, 29 against the action of a spring 23 or 24. The oil pressure control in chambers 28, 29 is effected by means of control system 25 and oil lines 26, 27, line 26 being in communication with oil reservoir 38. In oil lines 26,- 27 are incorporated check valves 35, 36 by means of which the pressure in chambers 28, 29 can be maintained, without the need of circulating oil continuously. The adjustment of the eccentric ring 22 determines the stroke of the piston 28. The connection between a pump chamber 31 and a line 32, on the one hand, to the supply and discharge openings 33, 34, on the other, is effected alternately by a distributing mechanism 37, depending on the position of the piston. It will be clear that the present invention is not restricted to the embodiment above discussed. Thus it is possible to employ other low-speed pumps having an adjustable stroke volume.

Claims: CLAIMS 1. A drive system for various consumers, such as pumps, aboard a ship, comprising a screw-driving motor, use being made of a motor-driven hydraulic pump which drives a hydromotor, characterized in that the hydraulic pump is a low-speed piston or plunger pump having a large adjustable strokevolume and arranged to directly drive the hydromotors, which directly drive those consumers that are necessary for maintaining the main drive or are otherwise associated with the main drive and/or supplies such consumers directly with hydraulic oil through adjusting means. 2. A drive according to claim 1, characterized in that the speed of the pump is lower than 1,000 rpm. 3. Adrive according to claim 1 or 2, characterized in that the adjustable stroke volume is about twice the maximum difference in stroke volume over the speed variation range of the screw shaft. 4. A drive according to any of the preceding claims, characterized in that hydraulic adjusting means for an adjustable ship's screw are connected to the hydraulic pump. 5. A drive according to claim 1 or 2, characterized in that the hydraulic pump is a radial piston or plunger pump. 6. A drive according to claim 1 or 2, characterized in that the hydraulic pump is a low-speed radial piston or plunger pump having an adjustable stroke volume. 7. A drive according to any of the preceding claims, characterized in that the plunger-piston rod support has a hydrostatic bearing. 8. A drive according to any one of the preceding claims, characterized in that the hydraulic pump is driven from the screw shaft of a ship through transmission means.

Inventors: BERG FRANS JOHAN VAN DEN, VAN DEN BERG, FRANS JOHAN
Applicants: SCHELDE NL
Application year: 1986
Main classification: B63J3
IPC codes: B63J3