A SHIP'S PROPULSION ARRANGEMENT AS WELL AS A METHOD FOR THE MANAGEMENT OF EXCEPTIONAL FORCES THEREIN The present invention relates to a propulsion arrangement as disclosed in the preamble of claim 1 and, correspondingly, to a method in accordance with claim 8. Especially, the present invention relates to such a ship's propulsion arrangement which includes a separate propulsion device housing which comprises a motor and a propeller, wherein said housing extends outwards from the ship's hull and is turnable. by means of primary power transmission means which include especially mechanical components. The present invention also relates to a method for the management of exceptional forces in connection with such a propulsion arrangement which extends outwards from the ship's hull and which can be turned by means of power transmission means which suitably include mechanical components.

Such ship's propulsion means, wherein a propeller is arranged at a structure which is separate from the hull and which structure, as such, can be turned and by means of which turning the propeller stream can be directed into a desired direction are well known in the maritime field. Thus, an ar- rangement built in this manner at the same functions as the ship's propulsion system and as the ship's main steering device. As it is, the motor can be located at any suitable place. If the motor is located within the hull the arrangement is usually such that the drive power to the propeller is trans- ferred via a shaft and a bevel gear arrangement. Again, an especially favorable embodiment of such a propeller arrange- ment includes à separate housing structure, a so called"pod", which usually is designed in a favorable shape with respect to the water stream, in which pod the driving motor for the propeller, in most cases an electric motor, is located. As an example of such an arrangement the propulsion system brought into the market under applicant's trade mark"Azipod" (TM) can be mentioned. Functionally, this kind of structure brings about a number of considerable advantages and for this reason such propulsion arrangements nowadays are adapted to the most various types of vessel.

Since a vessel at sea may get also into situations where ac- cidents or other situations of disturbance, which in them- selves should be avoided, might occur anyway, and this moreover under conditions where no external help can be obtained at least immediately, very serious attention has traditionally been paid in ship design to the reliability of operation also in exceptional situations. In the equipment this is taken into account, i. a., by means of a striving to redundancy of the most essential equipment so that at substituting arrangement is available if the main arrangement fails. Since a structure which is located outside the ship's actual hull often is relatively vulnerable, e. g., with respect to the risk for a grounding, a special attention must be paid to the reliability of operation for such structures under all conditions.

The housing structure at a propulsion arrangement as discussed above constitutes this kind of structure extending outside from the ship's hull. Usually this kind of housing structure is arranged in a fixed manner to an arm structure which, in turn, is arranged in a turnable manner to the ship's hull in such a way that said housing and its propeller (s) are located below the vessel at a location which is hydrodynamically and operationally appropriate. In the same way such an instal- lation location is usually arranged in such a way that the propulsion device, as such, will be located within the ship's outermost extent and is thus in a way sheltered. Typically, in order. to turn the housing structure a turning rim or collar, which in most cases is toothed, is arranged at the upper end of the arm, at which turning rim a turning motor for turning the housing is arranged. This motor is controlled by the ship's steering arrangement, and may as such be of any kind suitable to this purpose. In most cases the power connection between the turning motor and said turning rim is arranged by means of a pinion gear arrangement so that the turning. motor acts directly at said turning rim and thus brings about a turning of the arm and the housing structure attached thereto.

Since this kind of propulsion-and steering unit., which in a sense is integrated, is in a central position with respect to the safe operation of the vessel a safeguarding of its functionality under all conditions is of vital importance. On the other hand, the propeller functionality often requires locating the propeller or, respectively, the propellers at such a place or places where the propeller and thus also the housing structure will often be exposed in a rather vulnerable way at the extreme points of the ship's hull or even outside of them. Thus, the dimensioning of all structures of the pro- pulsion device should be such that the propulsion arrangement without serious-damages stands the stress caused by ice or blocks of ice and even light grounding. Such stress will mainly be directed to the housing of the propulsion device and especially to its turning machinery. In most cases such an external power impact causes a torque which strives to turn the housing of the propulsion device in relation to the turning arrangement which is controlled by the steering device, and thus an excessive stress will be directed almost directly to the separate elements of the turning arrangement.

Although the propeller is often considered to be the most vulnerable part of the arrangement the exchange of a broken propeller is not a very complicated task, as such. However, repairing or exchanging a turning machinery or a part thereof may often be a task of considerable complexity, especially due to the fact that the location of the machinery or its elements is often very inconvenient. For this reason the problem has until now been solved by dimensioning the entity comprising the turning rim and the turning motor considering also the stress calculated to constitute a predictable result of the exceptional forces included in the bases of dimensioning.

Thus, the parts of a turning arrangement are often heavily oversized in relation to the actual function. However, breakages still occur, where even an apparatus thus dimensioned has not endured still higher excess stress, against which a safeguarding, however, would have been structurally or economically inappropriate. Especially rapid blows directed against a pod structure have proved problematic since their momentary energy burst can rise to a considerable magnitude.

The object of the present invention is to solve the aforesaid problem so that a turning arrangement is achieved which is safer than known arrangements and wherein the dimensioning, however, can be based on the loads relating to the daily use.

A further object of the present invention is to disclose such an arrangement wherein an overload caused by even an extreme exceptional load does not bring about any permanent damage to the apparatus but where the ship's performance without any separate measures is guaranteed also after, e. g., a light grounding, and especially so that a resetting of any security arrangement, and thus a continuing of the safe operation, generally-require no separate actions.

Further can be observed that although a self-retaining turning mechanism such as a worm gear or the like would be, as such, a favorable solution in many cases, but precisely the self- retaining property has prevented the use since a safeguarding against a damage caused by an exceptional load has been especially hard to achieve in such an arrangement. Thus, one object of the present invention is also to disclose such an arrangement which renders possible a use also of such turning arrangements which earlier have been considered impossible or at least inappropriate.

One further object of the present invention is also to dis- close such an arrangement wherein the need for service is as low as possible while the security still remains to its original extent.

These and other objects of the present invention are achieved by means of the arrangements and methods which are disclosed in the appended claims. Thus, an arrangement according to the present invention is characterized in that sliding means in- cluding a dampening arrangement are arranged on the path of -power transmission between said housing and the ship's hull, wherein said sliding means enable an additional relative turning of the propulsion means independently of a forced control by the main power transmission means. Correspondingly, the method according to the present invention is characterized therein that the propulsion device, due to the impact of an exceptional force and by means of sliding means including a damping arrangement is brought to turn in relation to said main power transmission means or some of their components.

The present invention will now be described in more detail with reference to one favorable embodiment thereof and to the appended drawings, wherein Figure 1 discloses as a general side view a part of a ship, at which a turning propulsion device known per se is installed, Figure 2 discloses in a corresponding sectional view the general arrangements for a known propulsion device, Figure 3 discloses schematically and seen from above the general arrangement for one embodiment in accordance with the present invention, wherein the damping primarily is based on a function of friction sur- faces, Figure 4 discloses as a partially enlarged view the arrange- ment according to Figure 3 as a section taken along line A-A, Figure 5 discloses in a corresponding manner the general ar- rangement of Figure 3 as a section taken along line B-B, where the turning arrangement, however, as such has been arranged in accordance with an alternative implementation, and Figure 6 discloses schematically how the power impact acting on the propulsion device develops as a function of time when a device in accordance with one embodiment of the present invention is. operating.

In accordance with Figure 1 a propulsion arrangement for a vessel 1 includes, as known per se, a housing structure 3 having a propeller 2 arranged at at least one end thereof, which housing among professionals in the field usually is called"pod". A vessel can have several such pods, which can be arranged at the stern as well as at the bow of the vessel.

As such, a pod 4 includes a main housing structure 3 as well as an arm portion 6 connecting it to the vessel's 1 hull 5. In the embodiment disclosed in the Figure said arm portion 6 further includes wings 7 acting as a kind of rudder surface, as disclosed in more detail in Figure 2. The actual housing portion 3 and its arm 6 are turnable around an axis which extends transversely in relation to the vessel 1, favorably essentially vertically around a turning axis C-C, in which case the apparatus entity at the same time acts both as the a pushing or propulsion device of the vessel 1 as well as as the its steering means, i. e. as a, rudder.

Figure 2 discloses that the actual propulsion unit favorably includes an electrical motor inside said housing 3, as well as any possible other. means for rotating the propeller 2. In order to turn the propulsion unit'in relation to the hull 5 of the vessel 1 a known arrangement as disclosed in Figure 2 comprises a tooth wheel rim 8 arranged at the upper end of said arm portion 6, which rim is rotated by means of a pinion wheel 10 rotated by a motor 9 in accordance with steering commands given at the ship's bridge 11. The arrangement further includes bearing and sealing arrangements for the arm,. which arrangements, as known per se, are disclosed in Figure 2 only allusively.

In known turning devices said tooth wheel rim 8, the structure of said turning motor 9 as well as said pinion wheel 10 are usually dimensioned taking into account exceptional forces caused by an accident or by extreme conditions, so that the structures as such stand also the loads caused by, e. g., blocks of ice or even by a light grounding. In a turnable propulsion device such loads primarily cause a tendency for the propulsion device to turn away from the direction indicated by the turning motor 9. Since such an application of force due to an exceptional shock torque caused by a blow can be manifold in relation to the turning force required for the normal steering of the vessel this has in practice lead to that said elements, i. e. said tooth wheel rim 8, turning motor 9, and pinion wheel 10 in fact by necessity have been dimensioned too heavily. In spite of this incidents have oc- curred where the operation arrangement of the propulsion device, due, e. g., to an erroneous operation of the vessel or for some other reason has been damaged even to such an extent that the vessel at the worst has completely lost steerability.

In most cases such an accident has been directed to the pinion wheel 10 and/or to the tooth wheel rim 8, which both are quite difficult to repair under conditions at sea.

. Figure 3 discloses, seen from above, a new turning rim arrange- ment in accordance with one embodiment of the present in- vention, which arrangement, as such, can be adapted instead of a prior art turning rim 8 as disclosed in Figure 8, favorably even so that an arrangement according to the present invention also can be adapted as a retrofitting to existing propulsion devices. In the embodiment disclosed in Figure 3 the toothed part of the turning rim is shown to have an internal toothing, but a turning rim having an external toothing as disclosed in Figure 2 is also possible, as is disclosed in more detail in Figure 5.

The turning rim arrangement according to the present invention includes at least two-parts which at least to a limited extent are mutually movable, i. e. mainly rotatable, where one of said parts, i. e. the actual turning rim 8', is in connection with the turning machinery 9, e. g., with said pinion wheel 10 or, in the case disclosed in Figure 5, via a worm wheel 20. The other part of the turning arrangement., in the disclosed embodiment a turning collar 12, is arranged in such a way that it is in an operational, i. e. a power transmitting, contact with the propulsion device 4, that is mainly with its arm portion 6. Between these elements 8'and 12 a transition possibility is arranged in accordance with the present in- vention so that an exceptional excess load, i. e. mainly a forced rotation of the device in spite of the control exerted by the turning machinery 9, primarily causes a slipping of said turning collar 12 in relation to said turning rim 8'. In order to render this slipping possible to control under normal conditions and to enable a retrieval of the steerability of the vessel after an excess load condition, slip damper means are arranged in accordance with the present invention, by means of which the energy caused by the slipping can be controlled without damage to the actual drive means 8', 9,10 20.

Thus, Figures 4 and 5 disclose an arrangement according to one favorable embodiment of the present invention, where the damping is achieved utilizing means including mutually inter- acting friction surfaces 13,13a, 13b. According to Figure 4, which discloses a section A-A of Figure 3, a friction ring portion 14 of said tooth rim 8'is arranged into pressure between a turning collar 12 constituted by two superimposed parts 12a and 12b. Thus, the possibility of a relative movement between parts 8'/14 and 12a/12b has been achieved, which in Figure 3 is presented by arrows in opposite directions. Due to the properties of the co-operating frictional surfaces 13,13a, 13b and a favorable arrangement according to one embodiment of the present invention this relative movement can be very controlled very strictly as disclosed in more detail below.

Figure 4 show that said tooth rim 8'favorably is arranged at the turning collar assembly 12,12a, 12b in such a way that said turning rim 8'is centered by said turning rim assembly 12,12a, 12b. In tangential direction, however, said turning rim 8'remains in contact with said turning collar assembly only via the frictional forces acting between said friction surfaces 13, 13a, 13b. Said turning collar assembly is in turn favorably in operational contact with the arm portion 6 of the propulsion device 4, e. g., via guiding pins 15 which mutually center said turning collar portions 12a, 12b, directly by means of an arrangement according to Figure 5 or in some other way known per se for achieving a shape lock connection so that the rotative torque of both said collar 12a and said collar 12b will be transferred to the propulsion device 4 and thus enables it to be turned in a desired way. The actual turning assembly is favorably fitted in a installation block 17 by means of a bearing arrangement 16 and other arrangements known per se required by the operation (not shown) which instal- lation block in its turn, in a manner known per se, is at- tached to the hull 5 of the vessel 1.

According to Figure 5 which partially discloses a section B-B of'Figure 3 said turning collar portions 12a, 12b in ac- cordance with an especially favorable embodiment of the present invention, are mutually connected by means of a screw assembly 18 so that the normal force of said turning collar portions 12,12a, 12b can be adjusted at least in the region of said friction portions 13,13a, 13b. In order to enable such an exact adjustment a cup spring 19 or the like resilient member is arranged at said screw assembly 18. Such a resilient member renders possible, by utilization of the tightening torque acting at said screw assembly 18, a very exact adjust- ment of the normal force acting at said friction surfaces 13 and thus also of the friction acting between said tooth rim 8' and said turning collar 12.

Figure 6 schematically discloses an example of how an impact force"F"directed towards a propulsion device 4 can develop as a function of time"t", e. g., when a vessel 1 meets an unforeseen obstacle such as a block of-ice, a stone or even a wrongly arranged quay structure so that the propulsion device hits the obstacle. In Figure 6 reference Fp represents a turning force considered normal in view of the normal steering operations and for which a conventional turning apparatus 8, 9,10 and 20 must. be dimensioned in any case. When the impact force grows so high that it exceeds a force Fl, which cor- responds to the starting friction set in accordance with the above, the friction ring portion 14 of said tooth rim 8'and the co-operating friction surfaces 13,13alb of said turning collar assembly 12, 12a, 12b will get into a mutual slip. Without this kind of slip the impact force in the case shown would rise in accordance with graph"x"to a value"F2" at which the. structure 8 and/or 10 and/or 12 would break unless it is dimensioned also for this kind of forces that are extreme compared to the forces of normal operation.

After a short"starting phase", i. e. after exceeding the starting friction, the impact force will set at a level"F3" due to the slip, and will remain at this level, again due to the slip, until the impact event has passed. In Figure 6 this event is shown in broken line"y". Thus, for the dimensioning of the structures 8 and 12 it is enough, according to the present invention, that they withstand the force"F1"within a suitable safety coefficient,"F1"Yrepresenting the starting friction. By means of an arrangement as disclosed in Figures 4 and 5 the starting friction force"Fj_"acting between the co-operating friction surfaces 13,13a, 13b and thus also the device's disengagement torque with respect to an excessive stress can be set very easily and securely into accordance with a required safety torque by adjusting the torque at the tightening screw assembly 18. In practice, this torque depends on many structural factors, of which especially the size, surface structure and material of said friction surfaces 13, 13a, 13b can be mentioned.

In shipbuilding industry one natural construction material is steel, which easily can be machined into a desired shape. In order to guarantee that such steel friction surfaces arranged at a vessel will remain reliable in operation through the years it is appropriate that they are arranged in such a way that corrosion is prevented. For this purpose different kinds of oil baths or some other treatment based on oils will be suitable, which has not been disclosed in the Figures in more detail. According to one embodiment of the present invention said friction surfaces 13,13am 13b or at least one of them is coated with Teflon (R), graphite or the like material with special frictional properties, or, alternatively, the structural elements of the arrangement can comprise parts manufactured of such materials.

In an arrangement based on friction the management of energy leads to a heating of the friction surfaces. In a typical moderate collision case the energy build-up during, e. g., about three seconds can be in the order of, e. g., about 3 MW, which energy in one structure in accordance with the present invention causes a rise of temperature of about 80°. Such a rise in temperature does not constitute any problem, as such, since the heat will be distributed essentially evenly into the friction ring portion 14 of the tooth rim 8'and, cor- respondingly, into the turning'collar 12. If necessary, a separate cooling arrangement (not shown) can be arranged in connection with said elements.

It is evident from the above that the arrangement according to the present invention under all conditions protects, e. g., the teeth of a pinion wheel. 10 or, according to Figure 5, also a worm wheel 20. Thus there will be no need to dimension these teeth against any shock torque caused by exceptional impact but only in accordance with the torque required by normal operation. The detachment or protective torque required for the protection of the structures can be exactly defined in accordance with the structurally quite simple embodiment presented above. As it is influence on the torque can also be effected by purely structural means. Thus, in a further developed embodiment of the present invention several such elements 14 and 12a, 12b, respectively, which constitute said friction surfaces are arranged in a superimposed manner, i. e. said friction arrangement 13 is built up as a multi-layer lamellated structure, and in another embodiment the arrange- ment comprises special wedge elements by means of which the press force between said elements 12a, 12b, 14 can, e. g., be momentarily raised by actively operating means.

The disclosed arrangement further brings the advantage that, e. g., the retrieval of the steering function does not require any separate arrangements or measures taken by the operator, perhaps except for a check of the tightening torque at said screw assemblies 18, e. g., in connection with normal maintenance of the vessel. In theory, the slip between said tooth rim 8'and said turning collar assembly 12 will be maximally 180° (i. e. the propulsion device 4 turns totally into the opposite direction), after which the starting friction between the friction surfaces 13,13a, 13b by itself has the effect that the grip between the tooth rim 8'and the turning collar assembly 12 again will correspond to the detachment force''F1''of the starting friction. Thus the device will be operational again immediately after an excess load and the vessel 1 can again be steered in a normal manner.

With respect to normal steering operations it is then appropriate that any position indication sensors (not shown) usually necessary for the steering operation and known per se are arranged at the main structure of the propulsion arrange- ment 4, i. e. in connection with, e. g., said arm portion 6, in which case the position between said turning collar 12 and said tooth rim 8', or any dislocation of said position, actual- ly has no impact on the vessel's steering arrangements.

The structure discussed above is totally self-retaining which is a considerable advantage taking in account that the device as such often will be located in fairly restricted spaces which are difficult to reach. Due to the structure of the system there is no disadvantage related to the fact that said tooth rim 8'and said turning collar assembly 12 after an exceptional function may be in a mutual disposition which differs from the original one, but the arrangement according to the present invention also includes the possibility (not shown) to arrange separate means which can be operated if necessary and by means of which the mutual position of said elements 8 and 12 can be returned, if necessary.

One further advantage of the present invention that it renders the use of also other self-retaining structural elements possible. Thus, a worm gear arrangement which until now, expressly due to the risk of damage, scarcely has been used but which provides considerable advantages, is now quite possible in connection with a turning machinery 9, which pro- vides completely new possibilities for the device constructors. In Figure 5 this has been schematically indicated by reference 20.

Above some favorable embodiments have been described, but for a person skilled in the art it is clear that the present in- vention can be implemented in many other ways as well within the scope of the appended claims.