SUBMARINE PROPULSION SYSTEM

Abstract: A submersible vehicle (2) has mounted at the end of arms (6, 7) thrust units (not shown) which act on the arm in the direction of the arrows (15). The arms (6, 7) are connected to the vehicle (2) by linkage mechanism (14). This mechanism (14) is arranged such that when a difference in thrust is applied of the ends of arms (6, 7) the torque on the arms (6, 7) acts via the linkage mechanism (14) to alter the position of the arms (6, 7) and hence the direction of thrust. This can be arranged to cause rotation of the vehicle (2) by applying a differential thrust to the thrust units mounted on the ends of the arms (6, 7) which thrust would otherwise be in a vertical direction to maintain the vehicle (2) in a stable hover position, the vehicle having a negative buoyancy.

Description: SUBMARINE PROPULSION SYSTEM This invention relates to a submarine propulsion system and specifically but not exclusively to a submarine propulsion system for an expendable unmanned underwater vehicle. In attempting to dispose of underwater mines it has been usual to place an explosive charge adjacent the mine and then detonate the explosive charge hoping that this will cause sympathetic detonation of the mines warhead, destroying the mine, or at least render the mines sensor and triggering mechanisms inoperative, rendering the mine harmless. Placement of such charges has been carried out by a human diver or by a remote controlled submersible. Both of these methods have drawbacks. The main drawback is the high risk to the diver or submersible and it is in fact due to the unacceptably high risk to the diver that submersibles are used. However the very high cost of a submersible able to carry an explosive charge to a mine location, deploy the charge adjacent the mine, and return to the mother ship makes loss of the submersible unacceptable, in addition the weight and bulk of the submersible is such that only a very limited number can be stowed aboard a warship and as a result the vehicles mine sweeping capability could rapidly be lost due to destruction of the submersibles. A further disadvantage is that the time taken to dispose of a mine is by these conventional methods is quite long due to the need to get the diver or submersible to a safe distance before detonating the charge and the need for the diver or submersible to return to the mother ship, which must always remain at a safe distance from the mine throughout the operation, to pick up fuπher explosive charges. Since the combined explosive effect of the mine warhead and the disposal charge may be very great the safe distance is relatively large. It has been proposed to overcome these drawbacks by employing an expendable remotely controlled submersible containing an explosive charge and simply moving the submersible into close proximity to a mine and detonating the charge, destroying the submersible and hopefully detonating the mine warhead or disabling the mine sensor and detonation mechanisms simultaneously. The bulk and expense of such an expendable submersible can be very much less than that of a conventional reusable submersible since there is no need to include any explosive charge deployment mechanism, the range and operational life need only be sufficient for a one way trip to the target mine and all ofthe control and power systems can be 'one shot' devices. In designing such an expendable submersible it has proved difficult to make the submersible easily and accurately controllable so as to ensure that it can be got into close proximity to the target mine before detonation while simultaneously keeping the submersible cheap and light so as to allow a large number to be carried aboard the mother ship and to allow large numbers to be purchased, the arrangement of motors and propellers to provide forward thrust and the necessary control surfaces to allow controlled horizontal and vertical movement of the submersible has proved particularly difficult. UK Patent Application Publication Number GB 2281538 attempts to solve the above mentioned problems. This earlier patent application discloses two embodiments, each comprising an unmanned underwater vehicle, cylindrical in shape, propelled by two propellers mounted on arms on either side of the cylindrical body. In both embodiments the arms can be rotated such that the propellers can either be faced in a forward direction, in order to propel the vehicle forwards, or in a vertical direction such as to raise or lower the vehicle, the vehicle having a negative buoyancy. In one embodiment disclosed in GB 2281538 the arms on which the thrust units are mounted are biased by a spring to a position whereby thrust is generated in a vertical direction. At higher levels of thrust the spring bias is overcome by the force on the arms and these pivot to a position where the thrust is directed in a rearward direction propelling the vehicle forward. In a second embodiment the direction of the thrust units is changed from vertical to horizontal by a transducer within the hull of the vehicle which rotates a shaft through 90° on which the arms are mounted. The two embodiments disclosed in GB 2281538, described above, are adequate for carrying a warhead into close proximity to a mine to be destroyed, where detonation of the warhead in close proximity to the mine destroys the mine by a sympathetic detonation occurring within the mine. However, more recently, mines have employed new explosive materials such as plastics explosive which are not susceptible to sympathetic detonation. In order to destroy such mines it is desirable to be able to accurately position a shaped charge adjacent the mine such that the blast from the shaped charge is actually focused within the mine to be destroyed. Another advantage of using a directional shaped charge is that even if used against a conventional mine a smaller charge can be used than would be required to ensure a sympathetic detonation and therefore the size of the vehicle carrying the charge can be reduced This results in a cheaper mine destruction vehicle and also enables more vehicles to be earned by mine clearance vessels It may also enable the vehicle to be small enough to be deployed from a helicopter In order to correctly position a shaped charge relative to a mine to be exploded, it is necessary not only to pilot the vehicle into close proximity to the mine but also to be able to fully control the manoeuvrability of that vehicle when it reaches the mine One requirement is to be able to rotate the vehicle in azimuth while the vehicle is otherwise stationary adjacent a mine Neither of the above described embodiments of GB 2281538 is able to achieve this low speed rotaϋon for at low speed the thrust is directed vertically in order to maintain a fixed depth It is desirable to be able to have full low speed manoeuvrability of the vehicle without any requirement for additional control functions or propulsion units on the vehicle According to a first aspect of the present invention there is provided a submaπne propulsion system for a submersible vehicle, the system compnsing two thrust units by which the vehicle is propelled, means for varying the thrust of one unit relative to that of the other umt, and a linkage mechamsm between the two units arranged such that the oπentation of one unit relative to that of the other unit is dependent on the thrust generated by that unit relative to the thrust generated by the other unit By employing thε present invention a differential in thrust between the two thrust units is harnessed by the linkage and used to control the orientation of the thrust units. Therefore the position of the thrust units can be controlled without the need to employ any further transducers. Preferably the thrust units are located on opposite sides of the vehicle and a component of the thrust is directed by each unit in a vertical direction such as to control the depth of the vehicle, whereby varying the relative thrust between the two units causes the units to direct components of thrust in opposing directions such as to cause the vehicle to rotate in azimuth. This enables the vehicle to be rotated in azimuth without the need to make any headway. However, a differential in the thrust will tend to cause the vehicle to list, and it is therefore advantageous that the vehicle further comprise means for altering the transverse centre of gravity of the vehicle to compensate for this. It will be appreciated that if the vehicle is allowed to list then as a result of that list a component of thrust will be generated in the opposite direction to which the vehicle is listing, causing the vehicle to traverse towards the list. This can be utilised to control the transverse position of the vehicle. Preferably the linkage mechanism is arranged such that when low levels of thrust are generated by the units the linkage mechanism causes the units to be oriented so that a substantial component of the thrust from each unit is directed in a direction perpendicular to the major axis of the vehicle, and such that when high levels of thmst are generated by the units the linkage mechanism causes the units to be oriented so that a substantial component of the thrust generated by each unit is an axial direction relative to the major axis of the vehicle. This permits directional control of the thrust to be achieved by controlling the magnitude of the thrust, and typically at low levels of thrust the thrust units will direct thrust in a substantially vertical direction. Thus at high thrust levels the vehicle can be propelled rapidly forward to a target, and when the target is reached a hover position can be adopted by reducing the levels of thrust apphed. The orientation of the vehicle can then be controlled by controlling the differential thrust between the two units. Advantageously at low levels of thrust the orientation of the units is dependent on the difference in thrust between the units, and at higher levels of thrust the linkage mechanism locks the relative position of the units such that the thrust from each unit is in the same direction. This enables the vehicle to be steered while travelling in a forward direction by applying a differential thrust between the units without any alteration in the position of the thrust units occurring, which would otherwise make the vehicle difficult to steer. According to a second aspect of the invention there is provided a remotely operated underwater vehicle incoφorating the above propulsion system preferably carrying an integral shaped charge warhead. Using a vehicle embodying such a propulsion system enables the warhead to be correctly positioned relative to a mine to be destroyed. One embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figures IA to ID show a submersible vehicle employing a propulsion system in accordance with the present invention in four respective modes; Figure 2 illustrates the linkage mechanism of the propulsion system employed in Figure 1 ; Figure 3 depicts the components of the linkage mechamsm of Figure 2; Figure 4A is a side view of apparatus for altering the centre of mass of the submersible vehicle shown in Figures IA to ID; Figure 4B is a cross section along the line IV-FV of Figure 4A; and Figures 5A to 5D schematically illustrate other manoeuvres which can be performed by controlling the centre of mass of the vehicle. Referring to Figure 1 A, there is illustrated a front view and a side view of an unmanned submersible mine counter-measures vehicle 1 comprising a hull 2 incoφorating a shaped charge warhead 3 (omitted from subsequent figures), to be positioned facing a mine, and two thrust units 4 and 5. Each thrust unit 4, 5 comprises an electric motor and small propeller but could be any other suitable form of thrust unit. Each thrust unit 4, 5 is connected by a respective motor arm 6, 7 to the hull 2 of the vehicle. In Figure 1 A the thrust units 4, 5 are depicted in a forward position in which position the vehicle will be propelled in a forward direction. In Figure IB the thrust units 4, 5 are illustrated in a vertical position whereby contiol of the thrust will raise, lower or maintain the position of the vehicle 1 which has a negative buoyancy. In Figure IC the thmst units are illustrated in a position which will be adopted when a differential low level thmst is applied. In this position thmst unit 4 will provide a forward component while thmst unit 5 provides a rearward component rotating the vehicle in azimuth as indicated by arrow 8. For the thmst units to adopt this position the thmst on unit 4 must be greater than that on thrust unit 5 which will tend to cause the vehicle to list as indicated by arrows 9 and 10. To maintain an upright position a mass within the vehicle is moved such as to shift the centre of gravity in a direction indicated by arrow 11. Referring to Figure ID there is illustrated the position thmst units 4 and 5 will adopt when the thmst from unit 5 is greater than that from unit 4, and this will cause the vehicle to rotate as indicated by arrow 12. Again, a differential thmst will tend to cause the vehicle to list but this can be compensated for by shifting the centre of gravity in the direction of arrow 13. Any list generated by differential thmst from units 4 and 5 can be compensated for automatically by the vehicle without any need for further control signals. Referring to Figure 2 there is shown the linkage mechanism indicated generally as 14 by which motor arms 6 and 7 are connected to the hull 2, indicated by the broken lines, of the vehicle 1. The thmst units, not shown for clarity, are mounted on the ends of the arms 6 and 7 and exert a force on the arms in the direction indicated by arrows 15. The working of the linkage mechanism 14 will be better understood from a study of Figure 3 which illustrates the various components of the mechanism. Referring to Figure 3 the two motor arms 6 and 7 are mounted via respective brackets 16 and 17 on respective spindles 18 and 19 which fit into traverse tube 20. The arms 6 and 7 are linked by differential link 21 which has spherical ends which locate in holes in brackets 16 and 17. The differential link 21 pivots about pivot pin 22 at its centre which protmdes from pivot plate 23. The pivot plate 23 is itself free to rotate about traverse tube 20. Because the differential link 21 is pivoted on pin 22, which is in turn held in position by pivot plate 23, the arms 6 and 7 are constrained by brackets 16 and 17 such that they can only move in opposite directions to one another, unless the differential link is displaced, the whole assembly being held together by rod 24 and nuts 25 and 26. The rod 24 passes through brackets 16 and 17, spindles 18 and 19, tube 20 and base plate 32. The arms 6 and 7 are further constrained by pins 27 and 28 which extend from respective mounting brackets 16 and 17 and engage in slots 29 in the pivot plate 23, only one of which can be seen. These slots restrict the total differential movement to approximately ±15°. Torsion spring 30 acts between flange 31 of base plate 32, which is mounted to the vehicle, and spring plate 33, the spring engaging in hole 34 of the spring plate, as can be more clearly seen from Figure 2. The spring urges the tail piece 35 of the spring plate 33 against the differential link 21 which urges both arms 6 and 7 into the position illustrated in Figure 2, and also Figure IB, which position is referred to as the hover position. When a differential, relatively low level thmst is appUed the difference in the turning forces applied to each bracket 16 and 17 will cause the differential Unk pin 21 to pivot about the pivot pin 22 causing the differential link pin 21 to be urged against one side of the tail piece 35 of the spring plate 33. Thus the spring plate 33 will urge the differential link back into a centring position when the thrust is equalised. As the thrust is increased the whole of the linkage mechanism will pivot about rod 24, which is held in position by passing through the base plate 32, against the force of the spring 30 acting on differential Unk pin 21. As the thmst increases further the respective thmst limit faces 36, 37 on brackets 16 and 17 will contact with the ends 38 A and 38B of thmst limit pin 38. Therefore above a certain thmst any differential in thmst will not alter the position of the thmst units, this being determined by the thmst limit faces 36, 37, and thus the thmst units will be held in a position as shown in Figure IA. In this position the units 4, 5 are sUghtly inclined to compensate for the negative buoyancy of the vehicle 1. In this position differential thmst can be applied to steer the vehicle to port or starboard whilst proceeding forward. Referring to Figure 4A there is shown the arrangement inside the hull 2 of the vehicle 1 by which the centre of gravity of the vehicle can be moved both transversely and axially. Figure 4B is a cross section along the line IV-IV of Figure 4A. Within the hull 2 there is a central rod 40 to which sprocket 41 is attached. The rod which forms the main chassis of the vehicle also supports gantry 42 via brackets 43. The gantry 42 supports a relatively large mass 44, typically the battery power pack for the vehicle, by means of runners 45. The gantry also supports a motor 46 for driving sprocket 47 which is connected to sprocket 41 via chain 48. Operation of the motor 46 causes the gantry and associated mass 44 to be rotated about spindle 40 which thereby traversely shifts the centre of mass within the hull. The gantry 42 also supports actuator 49 which rotates quadrant 50. Quadrant 50 is attached at point 51 to cord 52 which mns along the edge of the quadrant 50 and is attached to the mass at 53. Similarly cord 54 is attached to the quadrant at point 55 and the mass at point 56. Rotation of the quadrant causes the mass to move forward and aft within the vehicle shifting the centre of gravity accordingly. In addition to compensating for differential thmst as described above, the position of the mass can also be controlled by actuator 49 and motor 46 to permit other manoeuvres to be performed in the hover position, that is when the thmst units are in a vertical position relative to the main axes of the vehicle. In Figures 5A to 5D arrows 57 indicate the direction in which the centre of mass of the vehicle has been moved in order to adopt the orientation shown. Arrows 58 indicate the direction in which the vehicle 1 wiU move. From Figure 5 A it is seen that if the centre of mass is displaced aft then the thmst units 4, 5 which act against the negative buoyancy of the vehicle to control its vertical position will exert a component of thmst forward and will slowly move the vehicle 1 backwards. Similarly, as illustrated in Figure 5B, if the centre of mass is moved forward the thmst units 4, 5 wiU move the vehicle forward. Referring to Figure 5C, if the centre of mass is moved to the starboard side this will cause the vehicle to list to starboard and thus the thmst units 4, 5 will cause the vehicle to traverse in a starboard direction. Similarly, as illustrated in Figure 5D, if the mass is moved to port then the thmst units 4, 5 will cause the vehicle to traverse to port. The above describes an embodiment where the invention is used to enable the position of a mine counter-measures vehicle to direct a shaped charge at a mine. It wiU, however, be appreciated that the invention could be employed with other types of submersible vehicle, including manned vehicles.

Claims: CLAIMS I 1. A submarine propulsion system for a submersible vehicle, the system comprising two thmst units (4,5) by which the vehicle (1) is propelled, means for varying the thmst of one unit relative to that of the other unit, characterised in further comprising a linkage mechanism (14) between the two units (4,5) arranged such that the orientation of one unit relative to that of the other unit is dependent on the thrust generated by that unit relative to the thmst generated by the other unit. 2. A system as claimed in claim 1 wherein the thmst units are located on opposite sides of the vehicle and a component of the thmst is directed by each unit in a vertical direction such as to control the depth of the vehicle, whereby varying the relative thrust between the two units causes the units to direct components of thmst in opposing directions such as to cause the vehicle to rotate in azimuth. 3. A system as claimed in claim 2 further comprising means (43, 44, 46,48) for altering the traverse centre of gravity of the vehicle to compensate for any differential thrust applied. 4. A system as claimed in any preceding claim wherein the linkage mechanism is arranged such that when low levels of thmst are generated by the units the linkage mechanism causes the units to be oriented so that a substantial component of the thmst from each unit is directed in a direction peφendicular to the major axis of the vehicle, and such that when high levels of thrust are generated by the units the linkage mechanism causes the units to be oriented so that a substantial component of the thmst generated by each unit is an axial direction relative to the major axis of the vehicle. 5. A system as claimed in claim 4 wherein at low levels of thmst the orientation of units is dependent on the difference in thmst between the units, and wherein at higher levels of thmst the linkage mechanism locks the relative position of the units such that the thmst from each unit is in the same direction. 6. A system as claimed in any preceding claim wherein the linkage mechanism at low levels of thmst biases the thmst units to a position where the thrust produced by the units is parallel. 7. A remotely operated underwater vehicle comprising a propulsion system as claimed in any preceding claim. 8. A vehicle as claimed in claim 7 further comprising a warhead for the destruction of mines. 9. A vehicle as claimed in claim 8 wherein the warhead is an integral shaped charge. 10. A linkage mechanism for a submarine propulsion system as claimed in any one of claims 1 to 6. 1 1. A linkage mechanism substantially as hereinbefore described with reference to, or as illustrated in, the accompanying drawings.

Inventors: ADAMS RICHARD, ADAMS, RICHARD
Applicants: ADAMS RICHARD, MARCONI GEC LTD, ADAMS, RICHARD, GEC-MARCONI LIMITED
Application year: 1996
Main classification: B63G8
IPC codes: B63G7, B63G8