TECHNICAL FIELD This invention relates to a method and a Propeller Pitch Control Arrangement, comprising a propeller hub having a number of interface fittings for adjustable pitch positioning of a propeller blade, a positioning device, within said hub, having a number of propeller control interfaces and an actuator arrangement arranged to move and position said positioning device to enable varying pitch for said propeller blades.

BACKGROUND

The use of propellers providing adjustable pitch is of importance regarding many ships, to enable optimization of the propulsion. A conventional system to arrange for adjustability of the pitch of the propellers is based on a rather powerful hydraulic system. For many ships hydraulic systems requiring about 30 kW power are needed. It is evident that such a large need output of power implies disadvantages. This is especially apparent taking into account that there is always some leakage in big hydraulic systems and therefore the system has to be up and running more or less continuously, not at least to achieve sufficient cooling. As a consequence such an hydraulic system is rather costly. Moreover it leads to the creation of noise, which in many installations is undesired. Furthermore it necessitates a rather complex shaft design, since the shaft has to enable both supply and drainage from the two pressure chambers used in connection with a hydraulic piston that actuates positioning of the propeller pitch adjustment device. Finally it is also a hazardous design with regard to the environment, since it may lead to leakage of oil into the nature.

From US 5 498 135 there is known a Propeller Pitch Control Arrangement, comprising a propeller hub having a number of interface fittings for adjustable pitch positioning of a propeller blade, a positioning device, within said hub, having a number of propeller control interfaces and an actuator arrangement, comprising a motor device (in the form of an electrical motor) positioned adjacent said hub, arranged to move and position said positioning device to enable varying pitch for said propeller blades. However, this known solution uses a reduction gear in combination with a drive spool and pitch ring, which makes the design bulky and complex, which probably is the reason why that design concept has not been any success. Also WO9631390 and US 20040157509, in a similar manner present solutions that are bulky and complex, e.g. by the use of a non- unitary hub body in WO9631390 and by the use of an adjustment device forming multiple bodies in US 20040157509.

SUMMARY OF THE INVENTION It is an object of the invention to eliminate or at least minimize the problem mentioned above, which is achieved by means of a method and an arrangement comprising a propeller hub having a number of interface fittings for adjustable pitch positioning of a propeller blade, a positioning device, within said hub, having a number of propeller control interfaces and an actuator arrangement driven by a motor device positioned adjacent said hub arranged to move and position said positioning device to enable varying pitch for said propeller blades, wherein said actuator arrangement includes a rotate able shaft with threads interacting with mating threads at said positioning device, and said motor device is powered by a generator having its rotating part connected to and driven by said hub.

Thanks to the invention there is created an arrangement that requires considerably less power in-put compared to conventional systems and which is cost-efficiently powered. As a consequence the arrangement will be considerably less costly both initially and also during use. Moreover it will facilitate a much more reliable solution regarding environmental aspects such as elimination of oil leakage. Furthermore it provides an arrangement that is much less noisy than conventional systems. All in all the new arrangement provides synergistic advantages that must be seen as surprising. Especially in combination with the use of a self braking transmission between the pitch adjustment device and the rotatable shaft these advantages are indeed surprising, since thanks to the use of a self braking interaction there will be no need for any other additional means to safe guard control to achieve a desired positioning, enabling a very compact design.

Further aspects and advantages of the invention will be more apparent in relation to the following detailed description.

BRIEF DESCRIPTION OF THE FIGURES

In the following the invention will be described in more detail, wherein; in Fig. 1, there is shown a side view of an embodiment of an arrangement according to the invention, and in Fig. 2 there is shown a cross-sectional view of the embodiment of the arrangement according to Fig. 1. DETAILED DESCRIPTION

In Fig. 1 there is shown a side view of a schematically presented embodiment of an arrangement according to the invention. There is shown a propeller hub 1 having adjustably attached propeller blades 200, and a pitch control arrangement as presented in Fig. 2. The hub present a hub body in the form of a unitary piece, that is propelled by a propeller shaft 9, attached to the front side IA of the hub 1. A casing 6 is attached to rear side IB of the hub 1. Within the casing 6 and also at the front end of a support 101 there is arranged a generator assembly 100. The support 101 is fixedly attached to a non-rotating part 110 attached to the hull of the ship, preferably a rudder horn 110, to which the rudder 120 is attached.

In Fig. 2 there is shown a propeller hub 1 having four interface fittings 10 for propeller blades 200. The hub 1 is fixedly attached to a propeller shaft 9 by means of a flange 90. A rotatable power shaft 2 is arranged coaxially with the propeller shaft 9, having one end 22 rotatably fixed to a bearing 31 in the end of the propeller shaft 9 and another bearing device 21 arranged in the outer wall IB of the propeller hub 1. The power shaft 2 protrudes through the outer wall IB where it is attached at its end to a motor 4, 5 by means of a conventional coupling device 41 (e.g. cotter joint). The motor 4, 5 is an electrical motor powered by means of a generator 100, having the stator 102 attached at the front end of the support 101, such that it encircles (but remaining a small gap) the rotor 103, which is positioned in the rear end of the casing 6, which is made in a polymeric material or any other kind of material enabling thorough flow of magnetic flux. The generator is connected to the stator 4 of the motor, to thereby provide power supply, upon rotation of the propeller shaft 9. A remotely controlled switching device 105 is preferably used to control activation of the pitch control actuator mechanism 4, 5, 2, 3. The transmitter/receiver 106 to remotely transmit/receive control signals is preferably positioned on the support 101, preferably on the inside of an annular part of the support 101 adjacent the casing 6. Thanks to positioning the control arrangement in this manner, and having the actuator mechanism 4, 5, 2, 3 powered by the generator 110 there is no need to transmit or transfer any signals or auxiliary power via the propeller shaft 9, enabling a homogenous shaft 9 which leads to considerable cost savings.

The motor 4, 5, in a conventional manner comprises a stator 4 that is fixedly attached to the hub 1, either directly to the outer hub wall IB and/or to a motor cover 6 that is also fixedly attached to the outer wall IB. The rotor 5 comprises an inner cylindrical portion 52 (locked to the shaft by means of 41) and windings 53 connected thereto. The power shaft 2 is arranged with outer threads 20 and passes through a nut device 31 having mating threads 30. The nut device 31 is fixedly attached (e.g. by means of screws 33) to the pitch adjustment device 3 centrally arranged within the hub 1. Accordingly by rotation of the rotor 52, 53 of the motor 4, 5 the shaft 2 will rotate and force the pitch control device 3 to move linear forward or backward, depending on direction of rotation. Upon movement of the propeller pitch control device 3, interface arrangements 34 that eccentrically and directly interact with each one of the propeller blades 200 will lead to adjustment of the pitch of each propeller blade 200, by rotation within the hub interface arrangement 10. Thanks to the use of self braking interaction between the threads 20, 30 an exact positioning of the propeller pitch adjustment device 3 may be achieved upon stop of supply of power, since the pitch adjustment device 3 will then stop exactly in the desired position without any delay.

An advantage with the shown embodiment is that many of the details used for this new pitch control adjustment arrangement are the same as those used in a conventional system. For instance the pitch control device 3, the hub 1, the interface 10 and 34 may advantageously be of the same kind as those used in known systems, which allows for cost efficient concept. As can be seen, thanks to the use of a self braking interaction between the threads 20, 30 the motor 4, 5 may fit into a relatively small space, enabling a motor cover 6 that is smaller in diameter than the hub 1.

The invention is not limited by what has been described above but may be varied within the scope of the appended claims. For the skilled person it is evident that the basic principles of the invention may also be used in connection with interacting threads not providing self braking, in at least some installations. Further it is evident that many other variations may be used without departing from the general principles of the invention, e.g. the use of different materials depending on specific needs/desires, etc. Further it is evident that in most applications the invention will be used in connection with a control system, including some kind of processor device interacting with some sensor device to control pitch of said propeller blades in an automatic or semi-automatic manner. In that regard it is evident to the skilled person that many different kinds of sensor means may be used for detecting the position of at least one propeller and/or the positioning device 3, and/or one or more parts of the actuator arrangement 2, 4, 5. The sensors may in a preferred mode use the same signal transmitting means as for other electric means, e.g. the electrical motor 4.