The invention relates to a rim driven thruster, a ship comprising at least one rim driven thruster and a method for propelling a ship.

Over the past years, an increasing effort has been made to provide cleaner and/or more efficient propulsion systems for ships. An example of a more efficient propulsion is a rim driven propulsion or rim driven thruster in which, contrary to conventional propellers, the propeller blades project inwardly from the inner wall of an annular rotor body. The annular rotor body is positioned within a, often also annular, stator body.

In order to further improve the efficiency and useability of the rim driven thruster, an open rim driven thruster having a central opening between the propeller blades was developed.

A disadvantage of the known rim driven thrusters is that such thrusters are complex and expensive, especially due to the fact that providing an efficient and effective radial and/or axial bearing has proven difficult.

The invention is aimed at obviating, or at least significantly reducing, the abovementioned disadvantages.

To that end, the invention provides a rim driven thruster, the rim driven thruster comprising: a stator body; an annular rotor body that is positioned in the stator and that comprises radially inwardly projecting blades;

- at least one axial bearing adjacent to the rotor, wherein the at least one axial bearing is configured to transfer and/or contain axial tilt and/or axial forces acting on the rotor body;

- an electromagnetic actuator system that is configured to selectively impart a driving force to the rotor; and an electromagnetic radial bearing between the stator and the rotor.

It is noted that the electromagnetic radial bearing is an active magnetic bearing configured to function as the sole radial bearing for the rim driven thruster according to the invention.

An advantage is that the mechanical complexity of the rim driven thruster is reduced with respect to the known rim driven thrusters. This is at least partially due to the reduced number of (mechanical) parts used in the known rim driven thrusters. It is especially true with regard to known rim driven thrusters in which (solely) mechanical bearings are used.

A further advantage of the rim driven thruster according to the invention, is that the use of lubricants that may pollute the water, such as grease and oil, is obviated. Another advantage is that the electromagnetic bearing obviates, or at least significantly reduces, frictional losses in the system. This also reduces the amount of wear on the rim driven thruster according to the invention when compared to the known rim driven thrusters.

A further advantage of the rim driven thruster according to the invention is that the use of an electromagnetic bearing reduces the noise emission of the thruster. This is due to the fact that the electromagnetic bearing, as sole bearing, obviates the use of other bearings and/or bearing components including bearing pads.

A further advantage is that only a single moving part is present in the rim driven thruster, thus significantly reducing wear on the system.

An even further advantage, due to the presence of the single moving part, the rim driven thruster has a strongly reduced noise emission compared to known rim driven thrusters.

In an embodiment according to the invention, the electromagnetic actuator system is configured to generate and/or maintain the electromagnetic bearing.

An advantage of this embodiment is that a highly compact thruster is achieved. This is mainly due to the fact that the electromagnetic actuator system is simultaneously used for generating the electromagnetic bearing and imparting the driving force or torque to the rotor. It is noted that the phrases ‘driving force’, ‘drive force’ and ‘torque’ are used interchangeably in this application and all refer to the same or a similar subject.

Another advantage of the thruster according to this embodiment is that, due to the combined functions in the electromagnetic actuator system, the complexity of the system, and most notably the mechanical complexity, is reduced.

A further advantage is that the thruster according to this embodiment is essentially maintenance-free, therewith reducing downtime and maintenance costs. This is mainly due to the reduction in mechanical complexity and the fact that electromagnetic bearing obviates the use of other bearings or bearing components that are subject to wear, such as bearing pads.

In an embodiment according to the invention, the rim driven thruster further may comprise a control unit that is configured for controlling the electromagnetic actuator system to selectively drive the rotor, wherein the control unit optionally may be configured for controlling the electromagnetic actuator system to generate and/or maintain the electromagnetic bearing.

An advantage of a control unit is that it allows the propulsion to be regulated by monitoring and/or adapting the rotation speed of the rotor.

It is preferred that the control unit is configured to control the electromagnetic actuator system with respect to both the electromagnetic bearing and the propulsion. A particular advantage thereof is that an integrated control of the actuator system is provided. In case any magnetic influence occurs between the electromagnetic bearing and the electromagnetic propulsion, the control unit is capable of adjusting the control signals to the electromagnetic actuator system to take these influences into account. Therewith, the robustness of the rim driven thruster is increased.

In particular, this embodiment allows a highly detailed and well-balanced control over both the electromagnetic bearing and the propulsion. It for example allows any consequences of deviations or changes in propulsion to be taken into account for the control over the electromagnetic radial bearing. A similar reasoning is true for the reverse case (i.e. compensation for changes in the electromagnetic radial bearing).

In an embodiment according to the invention, the control unit is configured to control the electromagnetic actuator system to provide the electromagnetic bearing by selectively and/or locally generating and/or adjusting radial electromagnetic forces to move the rotor into and/or maintain the rotor in a bearing position.

The control unit can be advantageously configured to control the position of the rotor by controlling the electromagnetic forces generated by the electromagnetic actuator system, therewith forming an active electromagnetic radial bearing. This allows the rotor to be brought into and/or maintained in the bearing position and obviates the use of other bearings. Especially during use of the thruster, the rotor and stator may be subject to various external (and often different) forces that have an effect on the position relative to each other. The control unit is preferably capable to control the electromagnetic actuator system at local positions to control the bearing and therewith to provide small and precise adjustments to the rotor to keep and/or bring the rotor and the stator in the correct relative position with respect to each other.

In an embodiment according to the invention, the electromagnetic actuator system comprises a number of magnetizable coils that is distributed along a circumference of the stator, and wherein the control unit is configured to control a current in the number of coils.

An advantage of having a number of magnetizable coils, especially magnetizable coils that can individually or groupwise be controlled, is that it allows a more precise control of the electromagnetic bearing and/or the rotation of the rotor. In addition, it allows the control unit to compensate for any deviations that occur due to external forces and/or the rotation of the rotor. This is especially relevant at higher rotation speeds due to the higher amount of force exerted on the bearing.

In an embodiment according to the invention, the number of magnetizable coils is at least four, preferably at least five, more preferably at least six, and even more preferably at least seven.

An advantage is that an increase in the number of magnetizable coils leads to a more precise control over the electromagnetic bearing and therewith over the relative position of the rotor in respect of the stator. It is therefore preferred to have at least four and preferably even more than four magnetizable coils to provide a precise control over the electromagnetic bearing. This also contributes to the use of the electromagnetic bearing as the sole bearing for the rim driven thruster according to the invention.

In an embodiment according to the invention, the number of magnetizable coils is three or a multiple of three.

An advantage of this embodiment is that three or multiples thereof can easily be substantially evenly positioned around the circumference of the stator.

In an embodiment according to the invention, the number of magnetizable coils depends on the radius of the rim driven thruster, and preferably wherein the number increases with an increase in the radius.

An advantage of increasing the number of magnetizable coils with an increasing radius of the rim driven thruster is that a precise control over the electromagnetic bearing can be maintained even at larger sizes of the rim driven thruster according to the invention. It is noted that although it is possible with a relatively small number of magnetizable coils to control the electromagnetic bearing, it has been found that a larger number is advantageous with larger radii of the rim driven thruster.

In an elaboration of one of the previous embodiments, the magnetizable coils are substantially evenly distributed along the circumference of the stator.

An advantage of a substantially even distribution is that it provides a well-balanced control over the electromagnetic bearing thus increasing its stability.

In an embodiment according to the invention, the rim driven thruster comprises a number of magnets, preferably permanent magnets, that are positioned on the rotor or are integral part thereof.

An advantage of providing magnets, especially permanent magnets, is that the electromagnetic bearing may (more easily) be realized.

In an embodiment according to the invention, the number of magnets is at least two, preferably four, more preferably six, even more preferably eight and most preferably more than ten.

An advantage is that the extend and precision of control over the electromagnetic bearing and therewith over the relative position of the rotor in respect of the stator increases with an increasing number of magnets.

In an embodiment according to the invention, the magnets are provided in magnet pairs.

In an embodiment according to the invention, the rotor is manufactured from a magnetizable material.

An advantage of providing a rotor of magnetizable material is that the necessity of using (permanent) magnets for the purpose of providing an electromagnetic bearing is reduced or even obviated. In an embodiment according to the invention, the rim driven thruster may further comprise at least one sensor that is configured to directly or indirectly measure a position, preferably a radial position, of the rotor with respect to the stator.

An advantage of providing at least one sensor is that this allows positioning data to be collected, which can advantageously be used in controlling the position of the rotor by means of the electromagnetic bearing. The relative position of the rotor with respect to the stator may effect the electromagnetic bearing. Conversely, the control actions taken with respect to the electromagnetic bearing may effect the relative position of the rotor and stator with respect to each other. Therefore, it is advantageous to have information regarding the relative position. This assists in mapping the mutual interference or influence between the bearing on the one hand and the relative position of the rotor with respect to the stator on the other hand. This allows a more precise control over the electromagnetic bearing and thus over the relative position of the rotor with respect to the stator. It is noted in this respect that in general in this application, the stator is chosen as fixed point in the relative positioning of the rotor and stator. This means that exercising control over the electromagnetic bearing is performed to change the position of the rotor and, therewith the relative position between the stator and the rotor.

It is further noted that the measurement data may be obtained using direct measurement, indirect measurement or a combination of both direct and indirect measurement. In case of a combination, preferably at least two different sensors are used.

It is noted that multiple sensors can be used that are positioned at various points along the circumference of the rotor and/or the stator. It is further noted that in some cases the position may be measured by an indirect measurement, for example by measuring a current (or a current amount) through magnetizable coils of the electromagnetic actuator system, or for example by measuring an electromagnetic field strength and/or deviations therein.

In an embodiment according to the invention, the at least one sensor is configured to measure one or more of: an electromagnetic field strength and/or deviations therein; and/or a current in (at least a portion of) the electromagnetic actuator; and/or a direct relative position between the rotor and the stator.

An advantage of this embodiment is that the positioning and/or integrity of the electromagnetic bearing can effectively and efficiently be monitored and controlled using the measurement data from the one or more sensors.

An advantage of using electromagnetic field strength, and especially deviations and/or variations therein, is that it provides accurate measurement data on deviations that can be used to control the electromagnetic bearing and/or the rotation of the rotor. This may for example be performed using a Hall-sensor. An advantage of measuring a current is that current sensors are robust and reliable, therewith providing a robust source of measurement data. A further advantage is that current sensors require a relatively small amount of space.

An advantage of a sensor that is configured to measure a direct relative position is that the information directly and unambiguously relates to the relative position of the rotor and the stator.

As such, it is noted that each of the sensor types mentioned above has distinct advantages with respect to the other. Combinations of different sensors may also be used to provide an (even more) redundant rim driven thruster.

In an embodiment according to the invention, the control unit may be configured to control the electromagnetic actuator system based on sensor measurement data to provide and/or maintain the electromagnetic bearing between the rotor and the stator.

An advantage of controlling the electromagnetic actuator system based on the sensor measurement data is that it provides a real-time and direct control of the electromagnetic bearing. As a result, the electromagnetic bearing can quickly and effectively be controlled and thus provides an increased stability and robustness. It is noted that providing and maintaining also includes, if necessary, correcting the position of the rotor with respect to the stator to maintain the electromagnetic bearing.

In an embodiment according to the invention, the sensor measurement data may comprise bearing data and rotation drive data, wherein the rim driven thruster further comprises a signal filter that is configured to separate the bearing data and the rotation drive data from each other.

An advantage of separating the measurement data in two different data streams is that a more detailed control is achieved. By separating the data streams, any deviations or necessary control actions become much easier to detect for the different functions, thus allowing a more precise control of the electromagnetic bearing.

In addition, it allows the control unit to distinguish between the different functions, which in turn allows both functions to be monitored independently from each other. As a result, a deviation or malfunctioning in either function can more easily be detected.

Furthermore, it allows a highly detailed and well-balanced control over both the electromagnetic bearing and the propulsion. It for example allows any consequences of deviations or changes in propulsion to be taken into account for the control over the electromagnetic radial bearing.

In an embodiment according to the invention, the at least one axial bearing comprises two axial bearings.

It is preferred that an axial bearing is provided on each of the opposite sides of the rotor to effectively position the rotor with respect to the stator. Each bearing preferably comprises a bearing surface on the side of the rotor and a number of tilting pads that is operatively connected to the stator and facing towards the bearing surface. As such, in this embodiment of the application the bearing function for the device is defined as having two separate bearings on either side of the rotor.

It should be noted that this however is a matter of definition. The application as such also encompasses a similar construction in which the bearing is defined as a single bearing having two ‘bearing sides’, which are positioned on opposite sides of the rotor. In essence, both definitions lead to similar or even the same technical/physical construction. These definitions may therefore be regarded similar and can be used interchangeably in the application.

In an embodiment according to the invention, the at least one axial bearing may comprise a hydrodynamic bearing.

An advantage of this embodiment is that, due to the combination of the hydrodynamic and the electromagnetic actuator system, only a single moving part is present in the rim driven thruster. This significantly reduces wear on the system, while simultaneously obviating the use of lubricants that may pollute the water, such as grease and oil.

Another advantage is that, mainly due to the presence of only a single moving part, the rim driven thruster has a strongly reduced noise emission compared to known rim driven thrusters.

A further advantage of a hydrodynamic bearing is that it facilitates a rim driven thruster with large diameter times revolutions per minute values. This allows the rim driven thruster to be used for larger ships.

A yet further advantage is that both bearings use or at least allow ambient water as lubricant, which obviates the need for (additional) seals. This in turn reduces the frictional losses incurred by such seals, leading to a more efficient propulsion.

In an embodiment according to the invention, the at least one hydrodynamic bearing may comprise a number tiltable bearing pads that are operatively connected to the stator and at least one bearing surface positioned on a side of the rotor, wherein the bearing pads and the at least one bearing surface are facing each other to form the axial bearing.

An advantage of providing tiltable bearing pads is that the bearing is adjustable, or even automatically adjusts, to changes in the (axial) forces exerted by the rotor. In addition, the tiltable bearing pads allow hydrodynamic operation of the rim driven thruster, which in turn reduces wear on the bearing .

In an embodiment according to the invention, the hydrodynamic bearing comprises a first bearing side that, viewed in an axial direction, is positioned on a first side of the rotor and a second bearing side that, viewed in an axial direction, is positioned on a second side of the rotor. The axial bearing is positioned such that it stabilizes the rotor and provides a bearing between the stator and the rotor. In the present disclosure, it means that both sides of the rotor are provided with at least one bearing surface and tiltable bearing pads are provided on or adjacent to each inwardly facing side of the stator to form the axial bearing.

It is noted that the operative connection may be a direct connection between the bearing pads and the stator or may be construed using a separate part with the bearing pads that, which separate part is connected to the stator.

In an elaboration of the abovementioned embodiment according to the invention, each bearing side comprises a number tiltable bearing pads that are operatively connected to the stator and an associated bearing surface positioned on the respective side of the rotor.

It is preferred that both bearing sides of the bearing, that the bearing sides on each side of the rotor, are provided with tiltable bearing pads to provide an optimal bearing performance.

In an embodiment according to the invention, the bearing pads may comprise a base layer and a coating, the bearing surface may comprise a material that has a hardness that is lower than a hardness of the coating.

An advantage of this embodiment is that the combination of a hard surface and a soft surface reduces sensitivity to wear through pollution or makes the bearing even substantially insensitive to pollution, such as sand and/or clay particles.

A particular advantage of providing the bearing pads on the stator, is that it provides a highly efficient bearing. Another advantage is that, when the bearing surface has worn out, the rotor can easily be replaced with another rotor to minimize downtime. The rotor that has been removed, can be refurbished by providing a new bearing layer on the rotor.

In an embodiment according to the invention, the base layer of the bearing pads is metal, preferably stainless steel, and the coating is a ceramic or semi-ceramic coating, wherein the coating preferably has a hardness in the range of 600 - 1 ,800 HV, more preferably in the range of 800 - 1 ,400 HV and even more preferably in the range of 800 - 1 ,200 HV and/or wherein the bearing surface is a polymer material, preferably a polymer material having a hardness that is lower than a hardness of the coating.

It has been found that the abovementioned materials, preferably with the mentioned hardness, combine an efficiently functioning bearing with a relatively low amount of wear of the bearing. It thus forms a good compromise between functionality and operational life-time.

In an elaboration of the abovementioned embodiment, the hardness of the hardest material in the bearing is chosen to exceed a hardness of sand. By choosing a hardness that exceeds the hardness of sand, the abrasive effect of sand on the rim driven thruster, and especially the rotor thereof, is reduced or even obviated. In an embodiment according to the invention, the bearing surface may comprise a base layer and a coating, the bearing pads may comprise a material that has a hardness that is lower than a hardness of the coating.

An advantage of this embodiment is that the combination of a hard surface and a soft surface reduces sensitivity to wear through pollution or makes the bearing even substantially insensitive to pollution, such as sand and/or clay particles.

This particular embodiment provides the advantage that the bearing surface, which is positioned on the stator, can easily be replaced.

In an embodiment according to the invention, the base layer of the bearing surface is metal, preferably stainless steel, and the coating is a ceramic or semi-ceramic coating, wherein the coating preferably has a hardness in the range of 600 - 1 ,800 HV, more preferably in the range of 800 - 1 ,400 HV and even more preferably in the range of 800 - 1 ,200 HV, and/or wherein the bearing pads are manufactured from a polymer material, preferably a polymer material having a hardness that is lower than a hardness of the coating.

It has been found that the abovementioned materials, preferably with the mentioned hardness, combine an efficiently functioning bearing with a relatively low amount of wear of the bearing. It thus forms a good compromise between functionality and operational life-time.

In an elaboration of the abovementioned embodiment, the hardness of the hardest material in the bearing is chosen to exceed a hardness of sand. By choosing a hardness that exceeds the hardness of sand, the abrasive effect of sand on the rim driven thruster, and especially the rotor thereof, is reduced or even obviated.

In an embodiment according to the invention, the axial bearing may have a thickness, measured in an axial direction, in the range of 5 - 50 mm, preferably in the range of 7.5 - 35 mm, more preferably in the range of 10 - 25 mm and most preferably about 15 mm, and/or wherein the axial bearing has a thickness, measured in an axial direction, in the range of 2 - 20% of a bearing diameter, preferably in the range of 3 - 15% of the bearing diameter, more preferably in the range of 4 - 10% of the bearing diameter and most preferably about 5% of the bearing diameter.

Ideally, the axial bearing thickness is as small as possible to reduce space requirements. It has been found that a thickness in the abovementioned ranges reduce the required space, while simultaneously allowing the bearing to function properly. It is noted that the abovementioned absolute ranges are examples for axial bearings with a predetermined thickness. More generally, the axial bearing thickness depends on the diameter of the bearing, which is represented by the relative ranges above.

In an embodiment according to the invention, a width of the bearing pads, measured in a radial direction, may be in the range of 2% - 30% of a rotor diameter, preferably in the range of 5% - 22.5% and more preferably in the range of 5% - 15% of the rotor diameter. It has been found that a (radial) width of the bearing pads in the abovementioned range supports the bearing function, while simultaneously reducing the amount of space required.

In an embodiment according to the invention, the number of bearing pads, when viewed along the circumference of the bearing, may be in the range of 3 - 42, preferably in the range of 9 - 30, more preferably in the range of 12 - 21 , and most preferably in the range of 12 - 15.

An advantage of the abovementioned number of pads is that it provides a good balance between bearing efficiency and the amount of material needed to manufacture the bearing. In general, the number of pads would be as low as possible from a manufacturing and material requirement view, whereas it would be as high to improve the functionality of the bearing. The abovementioned numbers have been found to provide a good balance between these requirements.

It is noted in this respect that other ranges regarding the number of bearings pads used may apply as well. It is especially noted that an increase in the load on the bearing generally requires an increase in the number of bearing pads used in the axial bearing.

In an embodiment according to the invention, the bearing pads, when viewed along the circumferential direction of the stator, may cover a portion of a surface of the stator in the range of 15% - 90%, preferably in the range of 25% - 80% and more preferably in the range of 40% - 65%.

In view of the abovementioned relation between the diameter and the number of bearing pads required, an advantage of this embodiment is that it takes scaling into account. It has been found that, regardless of the scale of the thruster according to the invention, the side surface of the stator, or the part to which the bearing pads are connected, covered by the bearing pads is preferably in the abovementioned range.

In an embodiment according to the invention, the rim driven thruster may comprise a thruster housing in which the stator and the rotor are positioned.

Preferably, a housing is provided in which at least the stator and the rotor are provided. The housing may be configured to be connectable to a ship, boat or other floating object.

In an embodiment according to the invention, the housing may be an elongated housing that extends substantially around a central axis of the rotor over a predetermined length and that has an inlet and an outlet, and wherein the housing is shaped to, during use, create a pressure difference between the inlet and the outlet.

An advantage of the abovementioned elongated housing is that it provides a more efficient propulsion due to the pressure difference between the inlet and the outlet.

In an embodiment according to the invention, the housing, when viewed along the central axis, may have a shape of a truncated cone. The housing may substantially be shaped as a cylinder or truncated cone. These forms provide a relatively low flow resistance when submerged in a fluid and simultaneously provide a central opening in which forces the water towards the rotor to provide an increased propulsion. This is especially true for a truncated cone in which the base is an inflow opening for water. In that case, the cone has a funnel-shaped opening in which the water is forced towards the rotor under an increasing pressure, which increases efficiency.

In an embodiment according to the invention, the elongated housing has a tunnel- of funnel-shape.

A tunnel- or funnel-shaped opening forces the water towards the rotor under an increasing pressure, which increases efficiency of the rim driven thruster.

The invention also relates to a ship comprising one or more rim driven thrusters according to the invention.

The ship according to the invention has similar effects and advantages as the rim driven thruster according to the invention. The ship according to the invention may be freely combined with any one of the embodiments as described for the rim driven thruster according to the invention. It is noted that a ship is also considered to include boats, barges, submarines and other self-powered moveable floating objects.

The invention further relates to a method for propelling a ship, the method comprising: providing a ship with one or more rim driven thrusters according to the invention; operating the one or more rim driven thrusters; and

- propelling the ship.

The method according to the invention has similar effects and advantages as the rim driven thruster and the ship according to the invention. The method according to the invention may be freely combined with any one of the embodiments as described for the rim driven thruster and/or the ship according to the invention.

In an embodiment of the method according to the invention the step of operating the one or more rim driven thrusters may comprise actuating an electromagnetic actuator system to provide an electromagnetic bearing and, selectively provide rotation to the rotor. The method optionally may comprise controlling, by a control unit, the electromagnetic actuator system to maintain the electromagnetic bearing. Further optionally, the method may comprise controlling, by a control unit, the electromagnetic actuator system to control a rotation speed of the rotor.

An advantage of this embodiment is that the electromagnetic bearing and the rotation of the rotor are simultaneously provided, which allows the thruster to have a relatively small size.

In an embodiment of the method according to the invention, the method further may comprises the step of directly or indirectly measuring a relative position of the rotor with respect to the stator. In addition, the method comprises the step of controlling based on measurement data obtained in the measuring step, the electromagnetic actuator system to maintain and/or correct the electromagnetic bearing. Optionally, the method comprises the step of filtering the measurement data from the measuring step to obtain bearing data related to the electromagnetic bearing and/or rotation drive data relating to a rotation of and/or torque exerted on the rotor.

An advantage of this embodiment is that, due to the use of the sensor measurement data, a more accurate control can be achieved. This allows a more rapid response or action to be taken to correct, if necessary, any deviations in the electromagnetic bearing. Therewith, a more stable bearing is achieved.

Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which:

Figures 1 A - 1 C show different views of an example of a rim driven thruster according to the invention;

Figure 2 shows a cross section along line IIB-IIB in figure 1 C;

Figures 3A and 3B show an example of a bearing ring for a rim driven thruster according to the invention;

Figure 4 shows an example of rotor and axial bearing of a rim driven thruster according to the invention;

Figure 5 shows a schematic example of a control for a rim driven thruster according to the invention; and

Figure 6 shows a schematic example of the method according to the invention.

In an example of a rim driven thruster according to the invention (see figures 1 A - 1 C), rim driven thruster 2 comprises housing 4, connector 6 and rotor 8. Connector 6 in this example is a connector to connect rim driven thruster 2 to a ship, boat or floating object to be propelled. Connector 6 may for example contain the electrical connection to an external power source and/or a connection with a control unit (not shown). It is noted that a control unit can also be provided in housing 4.

Rotor 8 in this example is provided with rotor blades 10, which extend radially inwards from rotor rim 12. It is noted that rotor blades 10 do not touch each other, thus leaving a throughflow opening 14 between rotor blades 10. As a result, rim driven thruster 2 is less susceptible to for instance pollution. It is noted that, in use of rim driven thruster 2, rotor 8 is rotatable around central axis A to generate forward or backward thrust P.

Rim driven thruster 2 (see figure 2) further comprises stator 16, which surrounds rotor 8 and in which rotor 8 is rotatable. Both stator 16 and rotor 8 in this example comprise parts of electromagnetic actuator system 18. Rim driven thruster 2 (see figures 2, 3) further comprises axial bearings 26, 28, which are positioned on opposite sides of rotor 8. Each axial bearing 26, 28 comprises respective bearing surface 30, 32 and an associated number of tilting bearing pads 34, 36. In this example (see figure 3), bearing pads 34, 36 are positioned on a respective axial bearing support 38, 40.

In another example, rim driven thruster 102 (see figures 4, 5), of which the features can be combined with the features of rim driven thruster 2 (shown in figures 1 - 3), comprises rotor 108 comprising rotor blades 110 which extend radially inwards from rotor rim 112 towards central axis A. Near central axis A, opening 124 is present, which prevents pollution.

Rim driven thruster 102 (see figure 4) further comprises axial bearings 126, 128, which are positioned on opposite sides of rotor 108. Each axial bearing 126, 128 comprises respective bearing surface 130, 132 that is positioned on rotor 108 and an associated number of tilting bearing pads 134, 136, which are in this example positioned on a respective axial bearing support 138, 140.

It is clearly visible (see figure 4) that rotor 108 is surrounded by stator 116 and is rotatable therein to generate thrust P in a forward or rearward direction.

Rim driven thruster 2, 102 may further comprise control unit 150 that is connected to electromagnetic actuator system 18, 118 to control operation of electromagnetic actuator system 18, 118 (see figure 5). In addition, rim driven thruster 2, 102 may additionally comprise one or more sensors 152, 154, 156 that are configured for generating measuring data. In this example, sensor 152 for example is a position sensor to measure the relative position of rotor 8, 108 with respect to stator 16, 116. Sensor 154 in this example is current sensor that 154 is configured to measure a current, which allows control unit 150 to calculate a relative position of rotor 8, 108 with respect to stator 16, 116. Sensor 156 represents any other sensor suitable for generating data with which control unit 150 can determine the relative position between rotor 8, 108 and stator 16, 116.

Based on the measurement data from the one or more sensors 152, 154, 156, control unit 150 is able to control electromagnetic actuator system 18, 118 to correct or maintain a proper electromagnetic bearing and therewith maintain the relative position of the rotor with respect to the stator. It is noted that in this example the electromagnetic radial bearing is the only or sole radial bearing of the rim-driven thruster.

Optionally, rim driven thruster 2, 102 may comprise signal filtering unit 158 that is configured to filter measurement data from current sensor 154. In this example, signal filtering unit 158 is configured to filter the measurement data in bearing measurement data and rotation measurement data, which are provided to control unit 150 separately. It can also be envisioned that control unit 150 is configured to perform such a filtering step. By separating especially the bearing measurement data from the other measurement data by applying a filtering step in the signal filtering unit 158 a more accurate control by control unit 150 is possible.

In use of rim driven thruster 2, 102, an electromagnetic bearing is provided by electromagnetic actuation system 18, 118. In addition, the application of a magnetic field by electromagnetic actuation system 18, 118 may also allow a torque to be imparted to rotor 8, 108 to rotate rotor 8, 108.

In an example of the method according to the invention (see figure 6), method 1000 comprises providing 1002 a ship with one or more rim driven thrusters according to the invention, operating 1004 the one or more rim driven thrusters, and propelling 1006 the ship. The step of operating 1004 the one or more rim driven thrusters may comprises several (sub)steps. A first step may be the step of actuating 1008 an electromagnetic actuator system to provide an electromagnetic bearing and, selectively provide torque to the rotor. Another optional step may be the step of controlling 1010, by a control unit, the electromagnetic actuator system to maintain the electromagnetic bearing, and optionally to control a rotation speed of the rotor.

The method may, alternatively, also comprise other method steps. This may for example include the step of actuating 1008 an electromagnetic actuator system to provide an electromagnetic bearing and, selectively provide torque to the rotor. Additionally, it may include the step of measuring 1012, by at least one sensor, a relative position of the rotor with respect to the stator and/or a current applied in the electromagnetic actuator system. A following step may be the step of controlling 1014, by the control unit and based on measurement data from the measuring step, the electromagnetic actuator system to maintain and/or correct the electromagnetic bearing to maintain the relative position of the rotor with respect to the stator, and the optional step of filtering 1016 the measurement data from the measuring step to obtain bearing data related to the electromagnetic bearing and/or rotation drive data relating to a rotation of and/or torque imparted to the rotor.

The present invention is by no means limited to the above described preferred embodiments and/or experiments thereof. The rights sought are defined by the following claims within the scope of which many modifications can be envisaged.