PITCH CONTROL UNIT FOR A CONTROLLABLE PITCH PROPELLER

Abstract

 A pitch control unit for adjusting the pitch of a controllable pitch propeller of a vessel using a mechanical system. The pitch control unit comprises a hollow drive shaft with an input side for receiving power from a prime mover and an output side for delivering power to the propeller. The pitch control unit further comprises a control motor and a screw assembly arranged around the hollow drive shaft. The control motor drives rotation of a rotatable body of the screw assembly and the screw assembly converts that rotation into an axial displacement of a travelling body of the screw assembly. The travelling body is connected to a coupling member that extends through the hollow drive shaft and is connected to an actuator rod that upon linear displacement actuates a blade pitch adjustment mechanism inside a controllable pitch propeller. The connection between the travelling body and the coupling member is arranged by a yoke assembly that translates together with both the travelling body and the coupling member, and that rotates along with the drive shaft. The invention further relates to a vessel and propulsion arrangement comprising such a pitch control unit.

Description

Technical Field

[0001] The invention relates to a pitch control unit for a controllable pitch propeller. Furthermore, the invention relates to a propulsion arrangement comprising such a pitch control unit, a planetary roller screw assembly for use in the pitch control unit and a vessel comprising such a pitch control unit.

Background Art

[0002] Controllable pitch propellers (CPPs) have been used for many years in vessels, e.g., sailing ships, motor boats, as an alternative to fixed pitch propellers or constant pitch propellers. In a CPP, the angle or pitch of the blades can be adjusted to suit the changing operating conditions of the propulsion system. This has several benefits such as easing the start of a vessel from a stationary position and making the vessel more manoeuvrable at low speed, providing the possibility to select an optimal pitch angle for the reduction of fuel use, turning the blades into a so-called feather position to minimize drag of the blades, or turning the blades into a position that enables the efficient conversion of energy during sailing.

[0003] A certain class of CPPs has a blade pitch adjustment mechanism in the propeller hub that requires a linear actuator to adjust the pitch angle. Currently there are at least two types of so-called pitch control units that can linearly actuate the blade pitch adjustment mechanism; hydraulic systems and mechanical systems.

[0004] A hydraulic system uses a hydraulic piston to generate axial translation by using oil pressure. When the hydraulic system is arranged inside a ship's hull, for example in front of the ship its gearbox, inside the propeller shaft, or integrated in the gearbox, the piston is connected to an actuator rod that extends through the propeller shaft. The axial position of the push-pull rod is measured using a mechanical position sensor, and dependent on the preferred mode of sailing, the axial position the actuator rod is adjusted. Any axial movement of the actuator rod is transferred to the blade pitch adjustment mechanism in the propeller hub. Nevertheless, elastic deformations of the actuator rod and leakages within the hydraulic system may result in a relatively low accuracy. In systems wherein the hydraulic piston is arranged in the propeller hub, there may be potential negative effects on environment when after a few years the hydraulic system starts leaking and the oil from the piston leaks directly into the water. In addition, hydraulic systems have high noise levels and are complex systems that require quite some maintenance.

[0005] Mechanical systems provide an alternative to hydraulic systems, but are typically suited for smaller vessels with less power. For example, French patent document FR 2146585 A5 discloses a mechanical actuator. A drawback of this system is that it is relatively large and complex, leading to low efficiency of the pitch control unit and high maintenance.

[0006] It would be desirable to provide an improved pitch control unit that enables the accurate linear actuation of a blade pitch adjustment mechanism in a controllable pitch propeller and reduces some of the disadvantages in existing systems as discussed above.

Summary of Invention

[0007] According to the invention, there is provided a pitch control unit for adjusting the pitch of a controllable pitch propeller. The actuating device comprises a hollow drive shaft arranged to rotate about its own central axis and having an input side for receiving power from a prime mover and an output side for delivering power to the propeller; a coupling member extending through the hollow drive shaft and arranged to rotate therewith, the coupling member further configured to be connected to an actuator rod of the controllable pitch propeller; a control motor; a screw assembly arranged around the hollow drive shaft, the screw assembly comprising a rotatable body, and a travelling body, wherein the control motor is arranged to drive rotation of the rotatable body and wherein the screw assembly converts the rotation of the rotatable body into an axial displacement of the travelling body, wherein the travelling body is connected to the coupling member within the hollow drive shaft by a yoke assembly that translates together with the travelling body and that rotates together with the drive shaft.

[0008] In this context, the term propeller is used to refer to the screw of a vessel. A controllable pitch propeller has a plurality of propeller blades whose angle or pitch may be adjusted during sailing of the vessel. It will be understood by the skilled person that the range over which the angle of the propeller blades may be adjusted is dependent on the specific application of the controllable pitch propeller and may typically vary between 40 degrees and 210 degrees. The pitch control unit can accurately adjust the blade angle over this full range.

[0009] The pitch control unit according to the invention only uses mechanical transmissions to accurately control the axial displacement of the actuator rod. This allows for an environment friendly system and reduces the risk of oil leakage, which is a problem in hydraulic systems. Moreover, the system can be relatively silent in comparison to existing pitch control units.

[0010] The screw assembly converts rotation into an axial displacement of the travelling member. The screw assembly may for example comprise a threaded inner screw and a rotatable nut, a ball screw, a roller screw, or a recirculating roller screw. Preferably, the pitch control unit is arranged along a straight line between the propeller and the prime mover to avoid unnecessary transmissions. The traveling body of the screw assembly preferably is configured to displace along the straight line.

[0011] In an embodiment, the screw assembly is a roller screw assembly comprising a nut, a plurality of planetary rollers and an inner screw. Use of a roller screw assembly in the pitch control unit has several benefits.

[0012] A roller screw assembly, such as a planetary roller screw assembly or an inverted roller screw assembly, enables high accuracy actuation. The high number of contact points between the planetary rollers and the nut and inner screw lead to a minimum backlash between the components and therefore the actuator rod can be adjusted very precisely. More specifically, the accuracy of a roller screw assembly is sufficiently high to comply with certain ISO norms on manufacturing tolerances for propeller blades. Certain embodiments of controllable pitch propellers may be manufactured according to the manufacturing tolerances of ship screw propellers of a diameter greater than 2,50 m as set out in ISO 484. According to a specific accuracy class, i.e., class I, the allowable angle difference with respect to the design angle is 0.2 degrees. When a roller screw assembly is used in the screw assembly, such accuracy may be obtained.

[0013] In addition, the pitch control unit can overcome the inaccuracy associated with elastic deformations of the actuator rod. When the propeller is in operation, the propeller blades also generate torque around the propeller blade base. These forces can be rather large, and may result in elastic deformations of the actuator rod in the magnitude of a few millimetres. These deformations in the actuator rod cannot be easily measured as the rod is arranged within the rotating hollow drive shaft. Nevertheless, the magnitude of the elastic deformations may be derived from the torque required by the control motorto adjust the position of the actuator rod. This torque may be combined with data on operational variables of the vessel, such as the vessel speed or the direction of currents surrounding the propeller to predict the elastic deformation. For example, a controller or control system that controls the control motor may compare the torque and operational variables to predetermined data that provide a prediction of the elastic deformation. The pitch control unit can accurately adjust the blade angle dependent on the predicted elastic deformation.

[0014] Further advantageous to a roller screw assembly is that very small corrections may be made, without requiring a minimum amount of adjustment. A hydraulic system would require a minimum amount of flow to overcome the internal resistance within the hydraulic system. This minimum amount of flow could easily result in an adjustment that is larger than the desired adjustment, thereby limiting the accuracy of a hydraulic system.

[0015] Moreover, the pitch control unit can bear high loads due to the high number of contact points between the rollers on the one hand and the nut and inner screw on the other hand. The planetary roller screw further allows for a quick adjustment of the position of the actuator rod. The lack of recirculating elements in a roller screw in comparison to, for instance, ball screws allows them to achieve higher speeds and accelerations. In addition, friction is typically very low and the adjustment is rather silent even at large speed. Consequently, a roller screw assembly has little friction, resulting in low maintenance costs and a long lifespan.

[0016] In an embodiment, the roller screw assembly is a planetary roller screw assembly, wherein the nut is the rotatable body and the inner screw is the travelling body. A planetary roller screw assembly has all the advantages of a roller screw as described above and in addition can be arranged in the pitch control unit in a relatively compact manner. Preferably, the nut is configured to rotate around the central axis of the drive shaft, and the inner screw is arranged symmetrically around the hollow drive shaft. Alternatively, the roller screw assembly may be inverted. This means that the rotatable body may be an inner screw and the travelling body may be a nut. In an inverted roller screw assembly, rotation of the inner screw is driven and the yoke assembly is connected to the nut. It will be understood that an arrangement wherein the inner screw carries the yoke involves less transmissions than an inverted roller screw and is less complex due to the travelling body being closer to the drive shaft.

[0017] The efficiency of the planetary roller screw assembly is very good because of the presence of the planetary rollers. The planetary rollers are in rolling contact with both an inner thread on the nut and with an outer screw thread on the inner screw. There is no relative axial movement between the nut and the planetary rollers because the effective pitch of the inner thread on the nut and a screw thread on the planetary rollers is the same. Therefore, the rollers and the nut can move axially with respect to the inner screw, but they do not move with respect to each other. During operation of the planetary roller screw assembly, the planetary rollers and the nut remain in constant rolling contact with each other, providing a transmission with little friction.

[0018] In an embodiment, the planetary rollers have a screw thread comprising a crest and a root, the crest and root being joined by a plurality of flanks, wherein each flank has a flank angle between 25 degrees and 60 degrees, preferably between 40 and 50 degrees, and more preferably around 45 degrees. The flank angle is defined as the angle between a flank and an axis perpendicular to the roller screw, wherein the axis perpendicular to the roller screw intersects the crest. Preferably, each flank angle in the planetary roller is the same, resulting in a thread shape that is symmetrical. A flank angle around 45 degrees provides a good balance in its ability to take up axial loads along a direction parallel to the drive shaft and radial loads along a direction orthogonal to the drive shaft. It will be understood that a larger flank angle increases the capacity of the rollers to take up axial loads, whereas a smaller flank angle increases the capacity to take up radial loads.

[0019] In an embodiment, the nut has an inner thread having an effective pitch between 15 mm and 50 mm. The screw thread of the planetary rollers and the outer thread of the inner screw may have the same effective pitch as the inner thread of the nut. Consequently, one revolution of the nut leads to an axial displacement of the actuator rod of approximately 15 to 50 mm. This allows for a reasonably quick control of the blade pitch. The effective pitch may be determined as the product of the number of starts and the thread pitch. In an exemplary embodiment, the nut has an inner thread having between 5 and 10 starts and a pitch between 3 mm and 5 mm, leading to an effective pitch between 15 mm and 50 mm.

[0020] In an embodiment, the planetary rollers have a screw thread with a thread shape configured to unwind in an inner screw thread of the outer nut or an outer screw thread of the inner screw. In this context the term "unwind" is used to indicate a minimum friction configuration wherein the thread shape of each of the planetary rollers, nut and inner screw are configured to allow the planetary rollers to travel around the inner screw and within the nut in a manner comparable to a planet wheel in a planetary gear system.

[0021] In an embodiment, the screw assembly is self-locking such that no adjustment in blade pitch occurs when rotation of the rotatable body is not driven. This contributes to safety and allows the blade angle to be maintained even when the control motor breaks down.

[0022] In an embodiment, the yoke assembly comprises a yoke carrier and a yoke element, wherein the travelling body houses the yoke carrier and wherein the yoke element extends through a plurality of lateral openings in a circumferential wall of the hollow drive shaft. The yoke element is carried by the yoke carrier and both translate together with the travelling body. The yoke element is locked in rotation with the drive shaft and this rotation is transmitted to the yoke carrier.

[0023] In an embodiment, the yoke element may be a beam connecting through two opposite lateral elongated slots in the hollow drive shaft. The elongated slots allow for displacement along the axial direction, whereas rotation with the drive shaft is locked. It will be understood that alternatively three or more elongate slots, preferably arranged in a rotationally symmetric manner, may be provided to allow the yoke to enter into the centre of the hollow drive shaft and be connected to the coupling member that extends through the hollow drive shaft.

[0024] In an embodiment, the pitch control unit further comprises a yoke bearing assembly for rotatably supporting the yoke assembly in the travelling body. The yoke bearing assembly permits rotation of the yoke assembly within the travelling body with low friction and thereby allows for decoupling of the rotation of the drive shaft and the travelling body.

[0025] In an embodiment, the yoke bearing assembly comprises a thrust bearing. The thrust bearing can support the axial forces transmitted through the actuator rod and allows for rotation of the yoke assembly around the central axis of the drive shaft. Examples of a thrust bearing include a tapered roller bearing, a deep groove ball bearing, a cylindrical roller bearing, a needle roller bearing, and a spherical thrust bearing. When sailing, the propeller thrust is directed through the hollow propeller shaft and actuator rod, and towards the hollow drive shaft and coupling member within the pitch control unit. The yoke bearing assembly absorbs the axial load from the coupling member, which is transferred to the yoke bearing assembly through the yoke assembly.

[0026] In an embodiment, the yoke bearing assembly comprises a spherical roller thrust bearing. Due to the spherical shape of the rollers, a limited amount of rotation around any axis orthogonal to the axis defined by the drive shaft is permitted. This allows the bearing assembly to compensate for any misalignments of the actuator rod and coupling member along the central axis.

[0027] In an embodiment, the pitch control unit further comprises a housing extending at least partially between the input side and the output side, and a main thrust bearing connected to the housing and arranged to absorb propeller thrust from the drive shaft and distribute it through the housing. Advantageously, the pitch control unit incorporates three functions: the transmission of torque from the prime mover to the propeller hub; the transmission of thrust from the propeller hub to the vessel; and the control of the blade pitch. The thrust absorbing function of the pitch control unit enables a flexible arrangement of the prime mover. The prime mover may for instance be placed at a position wherein sounds and vibrations of the prime mover have less negative effects on the vessel and the comfort of users.

[0028] In an embodiment, essentially all of the thrust is transmitted to the vessel through the pitch control unit and the prime mover delivers only torque. The skilled person will understand that part of the thrust will be transmitted through the shaft and the thrust bearing to the pitch control unit housing and the remainder of the thrust will be transmitted through the actuator rod and the yoke element via the yoke bearing assembly to the screw assembly. Alternatively, the thrust bearing may be arranged elsewhere, outside of the pitch control unit and the PCU may then only be required to deal with the portion of thrust transmitted through the actuator rod.

[0029] In an embodiment, the control motor is an electrical motor. The electrical motor may for instance be an electrical servo motor or an electrical stepper motor. An electrical motor is relatively silent and allows for precise torque control. Preferably, the electrical motor comprises an integrated sensor to track the blade pitch position. In a hydraulic system, due to the nature of hydraulics, where overtime pressure is leaking away, a separate measuring system is needed to check and verify the pitch setting. This measurement step introduces inaccuracy but is usable for most applications. When the sensor is integrated in the control motor, it can accurately keep track of the blade angle adjustment.

[0030] In an embodiment, a reduction gear assembly is arranged between the control motor and the screw assembly. The reduction gear assembly is arranged between the control motor and the screw assembly to reduce angular speed and increase the torque.

[0031] In an embodiment, a worm screw assembly comprising a worm screw and a worm wheel is arranged between the reduction gear assembly and the screw assembly. A worm screw assembly is highly suited for accurately controlling rotation of the nut of the planetary roller screw assembly and thereby also the axial translation of the actuator rod. In embodiments, the effective reduction ratio between the worm screw and the worm wheel is between 20:1 and 150:1. A worm screw assembly is further preferred from a safety perspective as a worm screw assembly can only be driven from one side, i.e., it can be driven from the side of the reduction gear assembly and the control motor, but not from the side of the worm wheel. Consequently, rotation of the worm wheel is blocked when the control motor is not running, resulting in a stationary position of the actuator rod and a constant blade pitch. The worm screw assembly thus contributes to the self-locking capability of the pitch control unit.

[0032] In an embodiment, the rotatable body of the screw assembly comprises the worm wheel. Selecting the worm wheel as the rotatable body further contributes to the self-locking capability of the screw assembly. In the case that the screw assembly is a planetary roller screw, the nut may comprise teeth along an outer circumferential surface, configured to be engaged by the worm screw. If the worm screw is not driven in rotation, rotation of the worm wheel, i.e., the nut, is blocked and the inner screw cannot travel along the axial direction.

[0033] In an embodiment, the pitch control unit further comprises a blade angle indicator and a sensor for measuring the position of the blade angle indicator. The blade angle indicator may be adjusted in position together with the actuator rod and used as an indicator for the position of the actuator rod and thus for the propeller blade angle. Preferably, the blade angle indicator is also accessible for physical observation in case of a power break down to check the blade angle position when all electronic systems are down.

[0034] In an embodiment, the screw assembly can be accessed manually to adjust the blade pitch. Manual access to the screw assembly allows the blade pitch to be adjusted even when the control motor is not functioning.

[0035] In an embodiment, the ratio between an outer diameter of the nut and an outer diameter of the drive shaft is at most 5:1, preferably less than 3:1. The planetary roller screw assembly thereby allows for a relatively compact pitch control unit. The compact dimensions provide flexibility for placing the pitch control unit at a preferred position along the propeller shaft and between the propeller and the prime mover.

[0036] In an embodiment, the pitch control unit is configured to allow for an adjustment of the propeller blade angle through a range extending over at least 40 degrees, or a range extending over at least 100 degrees, or a range extending over at least 210 degrees. It will be understood by the skilled person that the maximum range through which the blade angle can be adjusted is determined by the type of vessel and the desired modes of operation of the vessel, i.e., forward drive, backward drive, minimum resistance or an energy regenerating mode. The blade pitch adjustment mechanism in the propeller defines the minimum axial translation of the actuator rod that is required to achieve such a blade pitch adjustment.

[0037] In an embodiment, the pitch control unit is configured to allow for an adjustment of the axial position of the actuator rod of at least 7 cm, preferably at least 10 cm and more preferably between 10 and 40 cm. Within this range, the actuator rod may be adjusted very precisely.

[0038] According to a second aspect of the invention and in accordance with the advantages and effects described herein above, there is provided a planetary roller screw assembly for linearly actuating a rod extending through a rotating hollow shaft, the planetary roller screw assembly comprising a nut, configured to be driven in rotation by a control motor; a plurality of planetary rollers; and an inner screw configured to be translated axially consequent to rotation of the nut, wherein the inner screw carries a yoke assembly that translates together with the inner screw and wherein the yoke assembly rotates together with the drive shaft and is connected to the rod in the hollow drive shaft.

[0039] In an embodiment, an outer diameter of the nut is less than five times an outer diameter of the hollow shaft, preferably less than three times. The planetary roller screw assembly is preferably arranged tightly around the drive shaft, providing a compact assembly that can be mounted in a pitch control unit according to the invention.

[0040] In an embodiment, the planetary roller screw assembly is suitable for use in a pitch control unit according to the invention. Specific for a planetary roller screw suitable for use in a pitch control unit is its relatively large dimension and its configuration to house the yoke assembly within the inner screw.

[0041] According to a third aspect of the invention and in accordance with the advantages and effects described herein above, there is provided a controllable pitch propeller system for a vessel comprising a hollow propeller shaft; an actuator rod extending through the hollow propeller shaft; and a controllable pitch propeller. The controllable pitch propeller comprises a propeller hub connected to the propeller shaft for rotation about a longitudinal axis; a plurality of propeller blades mounted on the propeller hub, wherein each propeller hub has a blade angle that is adjustable by rotation about a respective pivot axis, each pivot axis being oriented radially with respect to the longitudinal axis; and a blade pitch adjustment mechanism arranged in the propeller hub and configured to adjust the blade angle of the propeller blades after linear actuation by the actuator rod. The controllable pitch propeller system further comprises a pitch control unit according to the invention for adjusting the blade pitch, wherein the propeller shaft is fixed to the input side of the pitch control unit and rotates together with the drive shaft. Here the longitudinal axis coincides with the central axis of the drive shaft.

[0042] According to an import aspect of the invention, the pitch control unit is arranged around the propeller shaft and drive shaft, and between the prime mover and the propeller hub. The pitch control unit provides access to the actuator rod and the coupling member extending through the hollow propeller shaft and drive shaft. This makes the arrangement very compact.

[0043] The pitch control unit is suited to be combined with various propeller systems. For example, propeller systems in large vessels typically allow for forward and backward sailing only. Such propeller systems may allow for a range of blade angle adjustment that is for instance 40 degrees or 50 degrees only. In other embodiments the propeller system may be tailored to sailing boats and also facilitate a so-called feathering mode for minimum drag, wherein a range of angle adjustment of for instance 110 degrees or 120 degrees is required. Finally, the propeller system may also be used on vessels to generate energy on board during sailing. In those applications, the range of adjustment of blade angles may be more than 180 degrees, for example 195 degrees or 205 degrees or 210 degrees. The pitch control unit may be configured to allow for enough axial translation of the actuator rod as is required by the blade pitch adjustment mechanism in the propeller.

[0044] In an embodiment, tthe hollow propeller shaft has a length of at least 4 m, preferably between 4 and 15 m.

[0045] According to a fourth aspect of the invention and in accordance with the advantages and effects described herein above, there is provided a propulsion arrangement for a vessel, comprising a pitch control unit comprising a drive shaft arranged to rotate about its own central axis and having an input side for receiving power from a prime mover and an output side for delivering power to a controllable pitch propeller; a prime mover arranged to drive rotation of the drive shaft; a central control unit, configured to control the operation of the vessel in different modes comprising at least a forward drive mode and a reverse drive mode; wherein the pitch control unit is structurally configured to receive all of the thrust of the propeller and transmit it to the vessel.

[0046] In an embodiment, the pitch control unit is a pitch control unit according to the invention.

[0047] In an embodiment, the propulsion arrangement further comprises a controllable pitch propeller and a propeller shaft, wherein the controllable pitch propeller is connected to the output side of the pitch control unit through the propeller shaft.

[0048] In an embodiment, the blade angle of the controllable pitch propeller can be adjusted over a range extending over at least 205 degrees and the propulsion arrangement further comprises an energy consuming device or energy accumulator, configured to receive energy regenerated by the controllable pitch propeller, wherein the central control unit is configured to control the operation of the vessel in different modes comprising at least a forward drive mode, a reverse drive mode, and a power regeneration mode. This enables an efficient regeneration of energy while the vessel is sailing.

[0049] In an embodiment, the prime mover has a capacity of at least 20 kW when turning at a speed of 200 and 1250 rpm, preferably at least 100 kW when turning at a speed between 200 and 1250 rpm. Current vessels of this size typically have a pitch control unit comprising a hydraulic system, which generates a lot of sound, is less accurate and is environmentally unfriendly.

[0050] According to a fifth aspect of the invention and in accordance with the advantages and effects described herein above, there is provided a vessel comprising a pitch control unit according to the invention or a controllable pitch propeller system according to the invention or a propulsion arrangement according to the invention.

Brief Description of Drawings

[0051] Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts. In the drawings, like numerals designate like elements. Multiple instances of an element may each include separate letters appended to the reference number. For example, two instances of a particular element "20" may be labelled as "20a" and "20b". The reference number may be used without an appended letter (e.g. "20") to generally refer to an unspecified instance or to all instances of that element, while the reference number will include an appended letter (e.g. "20a") to refer to a specific instance of the element.

Figure 1 schematically shows a cross-sectional side view of part of a vessel and the installation of a pitch control unit on board of the vessel.

Figure 2A schematically shows a front view of a first embodiment of the pitch control unit.

Figure 2B shows a cross-sectional side view of the pitch control unit in Fig. 2A.

Figure 2C shows a cross-sectional front view of the planetary roller screw assembly in the pitch control unit of Fig. 2A and Fig. 2B.

Figure 3 shows a perspective view of the nut and the planetary rollers in the planetary roller screw assembly in Fig. 2C.

Figure 4A shows a side view of a planetary roller in the planetary roller screw assembly in Fig. 2C.

Figure 4B shows an end view of the planetary roller in the direction IV-B in Fig. 4A.

Figure 4C shows a detail IV-C of the planetary roller in Figs. 4A and 4B.

Figure 5 shows a perspective view of the inner screw in the planetary roller screw assembly in Fig. 2C.

Figure 6 shows a perspective view of the drive shaft assembly in the pitch control unit according to Figs. 2A-2C.

Figure 7A shows a detailed perspective view of the worm screw assembly and electric motor in the pitch control unit according to Figs. 2A-2B.

Figure 7B shows a simplified cross sectional side view of a back-up positioning system in the worm screw assembly according to Fig. 7A.

Figure 7C shows a cross sectional front view of the back-up positioning system and the worm screw assembly in Fig. 7B.

[0052] The figures are meant for illustrative purposes only, and do not serve as a restriction of the scope or the protection as laid down by the claims.

Description of Embodiments

[0053] The following is a description of certain embodiments of the invention, given by way of example only and with reference to the figures.

[0054] Figure 1 schematically shows the side view of a part of a vessel 1. The vessel 1 is approximately 45 m long. A cross section through the hull 12 at the stern side 11 of the vessel 1 is provided, showing the installation of a controllable pitch propeller 3 and pitch control unit 4 on board of the vessel 1. The vessel 1 further comprises a motor and gear arrangement 5 and a propeller shaft 2 that connects the controllable pitch propeller 3 to the pitch control unit 4. The propeller shaft 2 defines a central axis C along its main axis.

[0055] The propeller shaft 2 is hollow and has a first end 21 that connects to the propeller 3 and a second end 22 that connects to the pitch control unit 4. A hollow stern tube 24 seals the connection through the hull 12 and prevents water from entering. The propeller shaft 2 is further supported by a shaft support 13 that extends downward from the stern side 11 of the vessel 1. An actuator rod 44 is housed within the propeller shaft 2, extending along the central axis C. The propeller shaft is approximately 5 m long.

[0056] The controllable pitch propeller 3 has a propeller hub 31, four propeller blades 32 and a blade pitch adjustment mechanism 37 inside the propeller hub. In forward or reverse drive mode, the propeller hub 31 receives rotary power from a motor and gear arrangement 5 on board of the vessel 1, which power is transmitted through the pitch control unit 4 and the propeller shaft 2. The propeller hub 31 rotates along with the propeller shaft 2, generating thrust and allowing the vessel 1 to propel forward or backward dependent on the propeller blade angle. The propeller blades 32 are rotatable around their blade base, allowing for adjustment of the blade angle. The skilled person will understand how the blade angle affects the generated thrust and how the blade angle may be optimized for various modes of operation of the vessel 1, such as forward drive, reverse drive, minimum drag position, and/or a power regeneration mode. Moreover, the skilled person will understand that the number of propeller blades 32 may be different in other embodiments, such as two blades, three blades, or five blades.

[0057] The blade pitch adjustment mechanism 37 is positioned inside the propeller hub 31 and only indicated schematically. The blade pitch adjustment mechanism 37 is configured to adjust the blade pitch upon linear actuation by the actuator rod 44 that extends through the propeller shaft 2 and between the pitch control unit 4 and the controllable pitch propeller 3. The blade pitch mechanism 37 may for example be a rack-and-pinion mechanism, or a mechanism where an eccentrically arranged pin in the propeller blade base is engaged with a sliding block in the propeller hub 31, allowing the blade base to rotate when the sliding block is moved along the central axis C.

[0058] The propeller shaft 2 rotates along the central axis C. The pitch control unit 4 is arranged on board of the vessel 1 and around the central axis C, between the hull 12 and the motor and gear arrangement 5. The pitch control unit 4 is thus placed in a straight line with the propeller hub 31, which enables direct and efficient control of the blade pitch adjustment mechanism 37, without loss of energy due to unnecessary transmissions.

[0059] The pitch control unit 4 has several functions, including the transmission of torque from the motor and gear arrangement 5 to the propeller shaft 2; the transmission of the thrust force from the propeller 3 and propeller shaft 2 to the vessel 1; and controlling the pitch of the propeller blades 32. The thrust absorbing function of the pitch control unit 4 provides flexibility in selecting where to arrange the motor and gear arrangement 5 . Preferably the motor and gear arrangement 5 is arranged at a position where negative effects due to vibrations and sound of the motor and gear arrangement 5 are minimized. The motor and gear arrangement 5 comprises a prime mover, which in this specific embodiment has a capacity of 1000 kW at a speed of 500 rpm.

[0060] Figure 2A schematically shows an outside front view of a first embodiment of the pitch control unit 4. The cross section through the actuator rod 44 is indicated in Figure 1.

[0061] The pitch control unit 4 has an output flange 42, behind which parts of a housing 45 are shown. The housing 45 has an opening at its top side where a worm screw assembly 46 driven by an electric motor 47 is provided. The pitch control unit 4 further comprises two supports 48 that allow for the installation of the pitch control unit 4 on board of the vessel 1.

[0062] The output flange 42 has a flange opening 52. The actuator rod 44 extends through the flange opening 52. The front side of the output flange 42 is further configured to be connected to the hollow propeller shaft 2.

[0063] Figure 2B shows a simplified cross sectional side view of the pitch control unit 4 in Fig. 2A. The pitch control unit 4 extends between an input flange 41 and the output flange 42. The input flange 41 and output flange 42 are connected through a drive shaft 43 that extends through the core of the pitch control unit 4. The drive shaft 43 is approximately 70 cm long, is hollow and has elongated slots 68 along part of its circumferential wall. The elongated slots extend between two stop edges 69. The drive shaft 43 further houses a coupling member 54. The coupling member 54 has a proximal end 55 that is connected to the actuator rod 44 and a distal end 56 screwed into a carrier nut 57 adjacent to the input flange 41.

[0064] The motor arrangement 5 can be connected to the input flange 41 to allow torque to be transmitted through the drive shaft 43 and the output flange 42 to the propeller shaft 2 and propeller 3. The output flange 42 is connected to the hollow drive shaft 43 by means of a hydraulic shrink fit.

[0065] The hollow drive shaft 43 is supported within the housing 45 through two bearing assemblies. The first bearing assembly is a main thrust bearing 40 that is arranged around the drive shaft 43 near the output flange 42 and absorbs the thrust force of the propeller 3. The thrust force is then distributed through the housing 45 and the supports 48 of the pitch control unit 4, and subsequently introduced into the hull 12 of the vessel 1. The thrust bearing 42 is arranged to allow thrust to be absorbed in two directions (i.e., for forward and astern sailing). The second bearing assembly 38 is a conventional ball type bearing, configured to primarily support radial loads.

[0066] Between the thrust bearing 40 and the input flange 41, a planetary roller screw assembly 49 is arranged, whose extent is indicated schematically with dashed lines. Main bearings 51 on both sides of the planetary roller screw assembly 49 rotatably support the planetary roller screw assembly 49 in the housing 45 of the pitch control unit 4, allowing rotation of the planetary roller screw assembly 49, while the housing 45 remains stationary. The planetary roller screw assembly 49 linearly actuates a coupling member 54, which is connected to the actuator rod 44 that extends through the hollow propeller shaft 2.

[0067] The planetary roller screw assembly 49 is driven by the electric motor 47, which will be discussed below with reference to Fig. 6 in more detail. The electric motor 47 generates torque that is transmitted via a worm screw 80 in the screw assembly 46 to the planetary roller screw assembly 49.

[0068] The pitch control unit 4 further comprises a back-up positioning system 79, which will be discussed in more detail with reference to Fig. 5B below.

[0069] Fig. 2C shows a cross-sectional side view of the planetary roller screw assembly 49 as indicated in Fig. 2B. Only the planetary roller screw assembly 49 is shown in Fig. 2C and other parts of the pitch control unit 4 have been omitted.

[0070] The planetary roller screw assembly 49 comprises a nut 61, eighteen planetary rollers 63, an inner screw 65 and a spacer ring 53. The nut 61 has a toothed circumferential strip 60 along its outer circumference. The worm screw 80 drives rotation of the nut 61 around the central axis C. Hence the nut 61 functions as a worm wheel in a worm drive comprising the worm screw 80 and the nut 61. The toothed circumferential strip 60 on the nut 61 comprises 92 teeth. The worm screw has 2 starts. The worm screw assembly therefore reduces the speed and increases torque by an effective reduction ratio of 46:1.

[0071] Fig. 3 shows a cut-open perspective view of the nut 61 and some of the planetary rollers 63. Along its inner circumference, the nut 61 has an inner thread 62 and a gear ring 58. The planetary rollers 63 have a screw thread 64 along their body and two outer ends 59. The inner thread 62 of the nut 61 and the gear ring 58 of the nut 61 engage with the planetary rollers 63. The two outer ends 59 of the planetary rollers 63 are provided with gear teeth that match the teeth in the gear ring 58 of the housing and ensures that the planetary rollers 63 are properly aligned with the nut 61 and rotate along with the nut 61. The gear ratio between the gear ring 58 and gear teeth 95 on the outer ends 59 determine the rotation speed of the planetary rollers 63. The outer ends 59 have protrusions 94 without gear teeth that are caged in the spacer ring 53, which keeps the planetary rollers 63 in position. The spacer ring 53 and gear ring 58 mechanically couple all planetary rollers 63 with each other. The gear ratio between the nut 61 and the planetary rollers 63 is selected such that the planetary rollers 63 do not show an axial displacement relative to the nut 61 due to rotation.

[0072] The inner screw 65 has an outer screw thread 66 along part of its outer circumference. The screw threads 64, 66 of the planetary rollers 63 and the inner screw 65 are configured such that rotation of planetary rollers 63 leads to a displacement of the inner screw 65 in a direction along the central axis C. The planetary rollers 63 spin in contact with, and serve as low-friction transmission elements between the nut 61 and an inner screw 65. The planetary rollers 63 create less friction than what the nut 61 and inner screw 65 would create when in a direct contact with each other. When the nut 61 rotates, the planetary rollers 63 rotate around their own central axis and orbit around the inner screw 65.

[0073] Figures 4A shows a side view of one of the planetary rollers 63. Figure 4B shows an end view of the planetary roller 63 in the direction IV-B in Figure 4A. Figure 4C shows a detail IV-C of the screw thread 64 of the planetary roller 63. The screw threads 64 of the planetary rollers 63 has a root 91 and a crest 92. The root 91 and crest 92 are joined by a plurality of flanks 93 at a flank angle ϕ of approximately 45 degrees. The flank angle is defined as the angle between a flank 93 and an axis perpendicular to the planetary roller 63. A flank angle ϕ of approximately 45 degrees enables a good transmission of both axial and radial forces. Moreover, the shape of the threads 64 and threads of the outer nut and inner screw are configured such that the threads 64 of the planetary rollers 63 unwind in both the inner thread 62 of the nut, 61 as well as unwind in the outer screw thread 66 of the inner screw 65. Therefore there is no slip of the planetary rollers 63, which contributes to a good accuracy and efficiency of the adjustments. In addition, the planetary roller screw 49 can support very heavy loads because of the large number of points of contact.

[0074] In this specific embodiment, the inner thread 62 of the nut 61 has 8 starts. The planetary rollers 63 have a pitch of 4 mm, which with the 8 starts in the inner thread 60 results in an axial displacement of 32 mm of the inner screw 65 per revolution of the nut 61.

[0075] Fig. 5 shows a perspective view of the inner screw 65 in Figure 2B. The inner screw 65 comprises an inner screw housing 71 with an annular chamber and a yoke bearing arrangement 74 arranged in the annular chamber. In the yoke bearing arrangement 74, a yoke carrier 72 is arranged. The yoke carrier 72 is annular shaped and has two yoke receptacles 73 along its circumference for receiving both ends of a yoke 67. The yoke 67 is indicated in Fig. 2B and 2C, where it is locked with its ends in the yoke carrier 72.

[0076] The yoke bearing arrangement 74 decouples the rotational movement of the yoke 67 and yoke carrier 72 that rotate along with the drive shaft 43, and allow the inner screw housing 71 to not rotate along. In this embodiment, the yoke bearing arrangement 74 is a spherical roller bearing, which can decouple rotation, absorb the axial loads acting on the yoke assembly and permits a limited amount of rotation along the spherical surface of the rollers to compensate for any bending of the actuator rod 44 and/or coupling member 54. The yoke assembly comprises the yoke carrier 72 and the yoke 67.

[0077] The inner screw 65 and the yoke assembly translate together along the axial direction upon actuation by the planetary roller screw assembly 49. The yoke 67 is moved through the elongate slot 68 in the circumferential wall of the hollow drive shaft 43. The stop edges 69 on both ends of the elongated slot 68 indicate the extreme positions between which the yoke 67 may be moved. The distance between the two stop edges 69 is approximately 15 cm.

[0078] The yoke 67 is connected to the coupling member 54, which connects to the actuator rod 44. Adjustment of the position of the inner screw 65 over a particular distance along the central axis C is thus directly translated into displacement of the actuator rod 44 over the same distance. The inner screw 65 with the yoke assembly enables the compact design of the pitch control unit 4.

[0079] Fig. 6 shows a more detailed yet simplified perspective view of the drive shaft 43 connected to the input flange 41 and the output flange 42. Adjacent to the output flange 42, the drive shaft 43 has a bearing spacer 35, configured to be received in the thrust bearing assembly 40. Between the bearing spacer 39 and the input flange 41, the drive shaft 43 has the two elongated slots 68. The yoke 67 extends through these slots 68 on both sides. The ends of the yoke 67 are received in the yoke receptacles 73 of the inner screw 65.

[0080] As explained above, the drive shaft 43 is hollow and within the drive shaft 43 the yoke 67 is connected to a coupling member 54 that is engaged with the actuator rod 44. Hence in this embodiment, both the coupling member 54 and the actuator rod 44 extend at least partially through the drive shaft 43. It will be understood, however, that for its functional purpose the actuator rod 44 could also be directly connected to the yoke 67 or even the yoke carrier 72. Nevertheless, including one or more additional coupling members 54 in the pitch control unit 4 eases the installation. Alternatively, the coupling member 54 could also extend beyond the output flange 42 and into the propeller shaft 2 and the connection between the actuator rod 44 and the coupling member 54 could be arranged within the propeller shaft 2.

[0081] The planetary roller screw assembly 49 enables a quick and accurate adjustment of the blade pitch. In this specific embodiment, 1 mm of axial translation of the actuator rod 44 results in a blade rotation of 1.4 degrees. As explained above, in one revolution of the nut 61, the axial displacement of the inner screw 65 and actuator rod 44 is approximately 32 mm. This means that one revolution of the nut 61 results in a blade rotation of approximately 45 degrees. Since the nut 61 can make 8 rotations per minute, the blade angle adjustment is very fast. It will be understood though by the skilled person that if the same pitch control unit is placed in another vessel having a propeller with a different blade pitch adjustment mechanism, the change in blade angle and the adjustment speed may be different. Further advantageous to the adjustment using the planetary roller screw assembly 49 is that the accuracy in the position is not significantly affected by the high adjustment speed.

[0082] The axial loads through the actuator rod 44 in this embodiment are typically up to 170 kN, resulting in elastic deformations up to approximately 1.7mm in the actuator rod 44. The pitch control unit comprises a control system (not shown) that predicts the elastic deformations and can control the control motor to adjust the blade angle accordingly.

[0083] Advantageous to the pitch control unit 4 according to the invention is that the pitch control unit 4 itself does not significantly deform consequent to these loads. Typically, it is difficult to accurately calculate deformation of the pitch control unit 4 and therefore a correction to compensate for a deformation within the pitch control unit would not be possible. The low deformation in the pitch control unit 4 results from the planetary roller screw assembly 49. The planetary roller screw assembly 49 has a minimal backlash in its components. Specifically, the backlash is much smaller than for other gear transmissions. This leads to a high accuracy of the pitch control unit and enables application of the pitch control unit in combination with propellers and propeller blades manufactured according to the ISO 484 norm, Class I. This norm allows for a pitch deviation of 0.75%, which results in an allowable angle difference of 0.2 degrees with regard to the design angle.

[0084] Figure 7A shows an outside top perspective view of the worm screw assembly 46 and the electric motor 47 that drive the planetary roller screw assembly 49. The electric motor 47 generates torque that is transmitted through an angular reduction gear 50 to the worm screw assembly 46. The arrangement of a worm screw assembly 46 between the electric motor 47 and the planetary roller screw assembly 49 provides several advantages, including a high accuracy and increased safety.

[0085] The electrical motor 47 is a servomotor with a first absolute encoder that can deliver up to 3000 rpm with a nominal torque of 9.5 Nm. The angular reduction gear 50 is arranged between the electric motor 47 and the worm screw assembly 46. The angular reduction gear 50 has two rotating gears that transmit the high speed incoming motion at low torque over a right angle (90 degrees) and a gear ratio of 8:1 to the worm screw 80. Specifically, the angular reduction gear 50 reduces the rotational speed from 3000 rpm to 375 rpm, while increasing nominal torque from 9.5 Nm to 76 Nm. The worm screw 80 rotates around an axis perpendicular to the central axis C. The worm screw 80 drives rotation of the planetary roller screw assembly 49. In the transmission between the worm screw and the worm wheel, i.e., the nut 61, rotational speed is further reduced to approximately 8.2 rpm whereas nominal torque is increased to 3496 Nm.

[0086] Opposite to the electric motor 47, a back-up positioning system 79 comprising an encoder 83, an angle indicator 78, and a position sensor 89 is provided. The back-up positioning system 79 allows for the visual inspection of the angle indicator 78 through a window 77 in a housing 76 of the worm screw assembly 46. The angle indicator 78 provides information on the blade angle. This allows an operator to always obtain information on the position of the blade angles, even if electronic systems on board of the vessel are not working. The change in position of the angle indicator 78 is linked to the movements of the worm screw 80 as explained below. The second encoder 83 checks the first absolute encoder of the control motor 47. The two encoders are automatically synchronized when either of the encoders is replaced.

[0087] Figure 7B shows a simplified cross sectional view through the worm screw assembly 46 (without the worm wheel) and back-up positioning system 79, wherein the housing 76 has been omitted. Figure 7C shows a front view of the worm screw assembly 46 (without the worm wheel) and the back-up positioning system 79 wherein a front side of the housing 76 has been omitted. The back-up positioning system 79 comprises a plurality of toothgears 81, 82, 84, 85, a trapezium threaded rod 86, a traveler 87 with magnet 88, and a sensor 89 for measuring the position of the magnet 88.

[0088] At an end of the worm screw 80 a toothgear 81 is provided. The toothgear 81 has 38 teeth and rotates along with the worm screw 80 around rotation axis R1. The toothgear 81 drives a control gear 82, which rotates around an axis R2 parallel to the rotation axis R1. The control gear 82 has 55 teeth. At the axis R2, a second control gear 84 is provided. The second control gear 84 is smaller and comprises only 23 teeth. The second control gear 84 drives rotation of a third gear 85, which rotates around a third axis R3, parallel to the axis R1 and R2. The third gear 85 has 48 teeth and is directly connected to the trapezium threaded rod 86 with a pitch of 3 mm.

[0089] The trapezium threaded rod 86 moves the traveler 87 with the magnet 88 along an elongated member 90 of the sensor 89. The sensor 89 measures the position of the magnet 88 and generates an analog signal that can be used as back-up in case of system failure. The traveler 87 further carries the angle indicator 78, which ensures that the blade pitch is always accessible for visually inspection through the window 77 in the housing 76.

[0090] As explained above, reversing the drive side from the worm screw 80 would block rotation. Hence in case of an electric failure of the control motor 47, the worm screw 80 would keep the same position. As a safety feature, the end of the worm screw 80 is manually accessible to enable adjustment of the propeller pitch in case the control motor 47 fails. The visual determination of the propeller pitch allows to keep track of the manual adjustment of the pitch.

[0091] The pitch control unit 4 is also relatively silent. The electrical motor 47, worm screw assembly 46 and planetary roller screw assembly 49 make very little sound in comparison to both a hydraulic system and a mechanical system using for instance planetary gear trains. In addition, the combination of the planetary roller screw 49 assembly and the worm screw assembly 46 is very safe. Advantageous to the use of a worm screw 80 is that it can only been driven from one side, i.e., the worm screw is driven from the side of the electric motor 47 through the angular reduction gear 50. Conversely, rotation of the nut 61 without actuation by the electric motor 47 would not lead to rotation of the worm screw 80. The worm screw assembly 46 is therefore safe to use since during a power outage this would result into a fixation of the blade pitch. Alternatively, if an electric motor 47 would drive the planetary roller screw assembly 49 through a different type of gear arrangement, continuous operation of the electric motor 47 would be required to secure the position of the actuator rod 44.

[0092] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. It will be apparent to the person skilled in the art that alternative and equivalent embodiments of the invention can be conceived and reduced to practice. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

[0093] Those skilled in the art and informed by the teachings herein will realize that the pitch control unit may be dimensioned based on the specific blade pitch adjustment mechanism in the propeller hub. The skilled person will understand that in traditional controllable pitch propellers suited for sailing in forward drive and reverse drive mode, rotation over an angle of 50 or 60 degrees is usually enough, whereas sailing vessels equipped with a so-called feather-mode for minimum drag might require a pitch adjustment over a range of 110-120 degrees. Finally, propellers that can be used also for power regeneration may require a rotation of the propeller blades beyond 180 degrees, preferably to a range of at least 205 degrees. It will be understood that the required axial displacement of the actuator rod in the propeller hub sets the dimension of the planetary roller screw assembly in the pitch control unit.

Claims

1. A pitch control unit for adjusting the pitch of a controllable pitch propeller, the pitch control unit comprising:

- a hollow drive shaft arranged to rotate about its own central axis and having an input side for receiving power from a prime mover and an output side for delivering power to the propeller;

- a coupling member extending through the hollow drive shaft and arranged to rotate therewith, the coupling member further configured to be connected to an actuator rod of the controllable pitch propeller;

- a control motor;

- a screw assembly arranged around the hollow drive shaft, the screw assembly comprising a rotatable body, and a travelling body, wherein the control motor is arranged to drive rotation of the rotatable body and wherein the screw assembly converts the rotation of the rotatable body into an axial displacement of the travelling body, wherein the travelling body is connected to the coupling member within the hollow drive shaft by a yoke assembly that translates together with the travelling body and that rotates together with the drive shaft,
wherein the yoke assembly comprises a yoke carrier and a yoke element, wherein the travelling body houses the yoke carrier and wherein the yoke element extends through a plurality of lateral openings in a circumferential wall of the hollow drive shaft.

2. The pitch control unit according to any of the preceding claims, wherein the screw assembly is a roller screw assembly comprising a nut, a plurality of planetary rollers and an inner screw.

3. The pitch control unit according to claim 2, wherein the roller screw assembly is a planetary roller screw assembly, wherein the nut is the rotatable body and the inner screw is the travelling body.

4. The pitch control unit according to claim 3, wherein

- the nut has an inner thread having an effective pitch between 15 mm and 50 mm; and/or

- the planetary rollers have a screw thread comprising a crest and a root, the crest and root being joined by a plurality of flanks, wherein each flank has a flank angle between 25 degrees and 60 degrees, preferably between 40 and 50 degrees, and more preferably around 45 degrees; and/or

- the planetary rollers have a screw thread with a thread shape configured to unwind in an inner screw thread of the outer nut or an outer screw thread of the inner screw; and/or

- a ratio between an outer diameter of the nut and an outer diameter of the drive shaft is at most 5:1, preferably less than 3:1.

5. The pitch control unit according to any of the preceding claims, wherein the screw assembly is self-locking such that no adjustment in blade pitch occurs when rotation of the rotatable body is not driven.

6. The pitch control unit according to any of the preceding claims, wherein the pitch control unit further comprises a yoke bearing assembly for rotatably supporting the yoke assembly in the travelling body, preferably wherein the yoke bearing assembly is a thrust bearing, more preferably a spherical roller thrust bearing.

7. The pitch control unit according to any of the preceding claims, further comprising a housing extending at least partially between the input side and the output side, and a main thrust bearing connected to the housing and arranged to absorb propeller thrust from the drive shaft and distribute it through the housing.

8. The pitch control unit according to any of the preceding claims wherein the control motor is an electrical motor.

9. The pitch control unit according to any of the preceding claims, wherein a reduction gear assembly is arranged between the control motor and the screw assembly, preferably wherein a worm screw assembly comprising a worm screw and a worm wheel is arranged between the reduction gear assembly and the screw assembly, more preferably wherein the rotatable body of the screw assembly comprises the worm wheel.

10. The pitch control unit according to any of the preceding claims further comprising a blade angle indicator and a sensor for measuring the position of the blade angle indicator, preferably wherein the screw assembly can be accessed manually to adjust the blade pitch.

11. A planetary roller screw assembly suitable for use in a pitch control unit according to any of claims 1-10.

12. A controllable pitch propeller system for a vessel comprising:

- a hollow propeller shaft;

- an actuator rod extending through the hollow propeller shaft;

- a controllable pitch propeller comprising:

- a propeller hub connected to the propeller shaft for rotation about a longitudinal axis;

- a plurality of propeller blades mounted on the propeller hub, wherein each propeller hub has a blade angle that is adjustable by rotation about a respective pivot axis, each pivot axis being oriented radially with respect to the longitudinal axis; and

- a blade pitch adjustment mechanism arranged in the propeller hub and configured to adjust the blade angle of the propeller blades after linear actuation by the actuator rod, wherein the controllable pitch propeller system further comprises:

- a pitch control unit for adjusting the blade pitch according the any of claims 1-10, wherein the propeller shaft is fixed to the input side of the pitch control unit and rotates together with the drive shaft.

13. A propulsion arrangement for a vessel, comprising:

- a pitch control unit comprising a drive shaft arranged to rotate about its own central axis and having an input side for receiving power from a prime mover and an output side for delivering power to a controllable pitch propeller;

- a prime mover arranged to drive rotation of the drive shaft;

- a central control unit, configured to control the operation of the vessel in different modes comprising at least a forward drive mode and a reverse drive mode;
wherein the pitch control unit is structurally configured to receive all of the thrust of the propeller and transmit it to the vessel.

14. The propulsion arrangement for a vessel according to claim 13, wherein the pitch control unit is a pitch control unit according to any of claims 1-10.

15. A vessel comprising a pitch control unit according to claims 1-10, a controllable pitch propeller system according to claim 12, or a propulsion arrangement according to any of claims 13 or 14.

Drawing