Patent Description:
Traditional marine propellers for the propulsion of vessels normally have a fixed pitch. A drawback at such fixed pitch propellers is that the chosen pitch can be optimal only for a limited rpm and speed. For optimal usage of the supplied power, the pitch should be low at start and low speed propulsion, whereas it should increase during acceleration to a high pitch at top speeds. The use of fixed pitch propellers therefor necessarily leads to a compromise in regard of acceleration, top speed and energy consumption.

It has therefore been suggested to provide marine propellers with variable pitch. According to one general design line, the pitch may be actively controlled in response to momentarily prevailing circumstances such as speed, rpm, load, supplied power, etc. Such actively controlled variable pitch propellers however need to be comparatively complex in construction and require intricate means for altering the pitch as well as means for determining the prevailing circumstances and systems for actuating the pitch altering means in response to the determined circumstances.

According to another general design line, it has been suggested to provide propellers having automatically self-adjusted pitch. <CIT> discloses such a variable pitch propeller with automatic adjustment. The propeller disclosed in this document comprises a hub and a plurality of blades which are journaled on the hub on axes, each in a plane radial to the hub to permit rotation of each blade to vary its pitch angle. The known propeller further comprises resilient means for applying a biasing torque to the blades urging them in a direction toward the greatest pitch angle. The resilient means are responsive to the fluid pressure load on the blades and comprises a first and a second cam which are movable relative to each other and urged against each other by a spring unit. Other propellers of the kind are known from documents <CIT>, <CIT> or <CIT>.

<CIT> discloses another variable pitch propeller comprising helicoidal blades mounted on a hub to freely pivot about a radial axis. The pivot axis of each blade is positioned behind the blade, with respect to the direction of the axial movement of the propeller through the water and in front of the blade's centre of mass in the rotational direction of the propeller and arranged such that, when the propeller is rotated in the absence of hydrodynamic forces, centrifugal effects cause the blade to adopt a pitch substantially equal to the pitch of the helicoid. Such an arrangement of the pivotal axis in combination various requirements on the blade rake, a certain skew-back shape, the pitch ratio and the aspect ratio is said to cause the centrifugal forces and the hydrodynamic forces to act in combination to cause the blade to adopt a position which produces a substantially optimum thrust over a range of rotational and axial speeds.

An object of the present invention is to provide an enhanced self-adjusting variable pitch propeller for marine use.

Another object is to provide such a propeller which, at use, provides enhanced performance with regard to i. faster acceleration, higher top speed, lower energy consumption, reduced slip and increased manoeuvrability.

A further object is to provide such a propeller which is reliable in use and allows for a comparatively long service life.

Yet another object is to provide such a propeller which facilitates service and repair.

Still a further object is to provide such a propeller which is comparatively simple in construction and which comprises a comparatively low number of constituent components.

Yet an object is to provide such a propeller which may be manufactured at a comparatively low cost.

The term "pitch" is used to describe the linear distance that the propeller would move in one complete revolution through a solid medium not allowing for slip.

According to a first aspect, the present disclosure provides a self-adjusting variable pitch propeller for marine use as defined by the appended claim <NUM>. The propeller comprises a central hub with an axial propeller centre line defining the rotational axis of the propeller and a plurality of blades extending radially from the hub. The hub exhibits a central bore arranged to receive a rotating drive shaft. Each blade is pivotally fixed to the hub and pivotal about a respective blade pivot axis which extends radially from the hub through the respective blade. Each blade exhibits a leading edge, a trailing edge, a pressure side exhibiting a pressure side area and a suction side exhibiting a suction side area. The blades are mechanically inter-connected to freely transfer pivotal movement of each blade to all other blades. The pivotal axis of each blade is positioned such that > <NUM>% of the suction side area and of the pressure side area is arranged between the trailing edge and the pivotal axis of the respective blade.

At self-adjusting variable pitch propellers, the hydrodynamic forces acting on the pressure and suction sides of the blades strive to pivot each blade in opposite directions. The forces acting on the suction side strive to increase the pitch whereas forces acting on the pressure side strive to decrease the pitch. The acting forces varies greatly with varying rpm and the propeller's axial speed through the water. In addition, the three dimensional geometry of the blades, such as the curvature and the distribution of the blade area along the radial distance from the propeller's rotational axis greatly influence the balance between the forces striving to increase and reduce the pitch. The propeller according to the present disclosure is based on the realization that the distribution of the blade's pressure side area and suction side area in relation to a pivotal axis extending through the blade is of great importance for achieving an advantageous self-adjustment of the pitch over a wide range of propeller rpm, axial speed through the water and load. Specifically it has been found that an optimal self-adjustment of the pitch is achieved over such a wide range when the pivotal axes extending through the blades are positioned such that more than half of the suction side area and more than half of the pressure side area of each blade is arranged down-stream, in the rotational direction of the propeller, of the respective pivot axis. In other words, more than half of the suction side area and of the pressure side area is arranged between the pivot axis extending through the blade and the trailing edge of the blade.

By such an arrangement it has proven possible to achieve that the blades automatically assume an advantageous and at least close to optimal pitch for each rpm when the vessel accelerates from still standing to top speed. By this means the acceleration of the vessel is increased and the energy consumption is decreased at the same time as the manoeuvrability is enhanced and the top speed may be increased. The propeller may thus enhance the overall performance of the vessel and at the same time reduce the environmental impact of its use. The comparatively simple criteria for achieving these advantageous effects may also readily be implemented at various propeller types and designs such that the propeller may be realized with a comparatively low number of constituent parts. This in turn enhances the reliability and service life of the propeller and facilitates simple manufacturing at low cost. The propeller may further readily be designed to allow easy assembling and disassembling such that service and repair is facilitated.

According to an embodiment of said first aspect, ≤ <NUM> % of the suction side area and ≤ <NUM> % of the pressure side area is arranged between the trailing edge and the pivotal axis of each blade.

Each blade may be limitedly pivotal about the pivot axis between a minimum and a maximum pivot angle.

Each blade may be formed such that the minimum pivot angle corresponds to a pitch of <NUM>. <NUM> (<NUM> inch) and the maximum pivot axis corresponds to a pitch of <NUM>, <NUM> (<NUM> inch).

Each blade may be fixed to or formed integral with a respective blade root.

The blades may be mechanically inter-connected by means of a gear arrangement.

The gear arrangement may then comprise first gear teeth arranged on each blade root and second gear teeth arranged on at least one interconnecting member.

The at least one interconnecting member may comprise a ring-shaped member and the second gear teeth of the ring-shaped member may mesh with the first gear teeth of all blade roots.

The at least one interconnecting member may comprise a plurality of cog wheels and the second gear teeth of each cog wheel may mesh with the first gear teeth of two mutually adjacent blade roots.

The hub may exhibit an axially extending exhaust channel for transportation of exhaust gases.

The exhaust channel may be annular and arranged concentrically around the central bore of the hub.

The hub may comprise an exhaust turbine which is fixed to the hub and arranged in the exhaust channel.

The hub may comprise a central sleeve exhibiting the central bore and a peripheral sleeve concentrically arranged with and outside the central sleeve thereby forming the exhaust channel between the central sleeve and the peripheral sleeve.

The peripheral sleeve may be connected to the central sleeve by means of helically arranged spokes which form respective turbine blades of the exhaust turbine.

The hub comprises at least two segments which are mutually fixed one after the other in the axial direction of the propeller and wherein the blades are fixed to the hub at respective recesses formed in the hub at the junction between two segments.

The number of blades may be between two and eight, preferably between three and five.

According to a second aspect, the present disclosure provides a self-adjusting variable pitch propeller for marine use which propeller comprises a central hub with an axial propeller centre line defining the rotational axis of the propeller and a plurality of blades extending radially from the hub, wherein the hub exhibits a central bore arranged to receive a rotating drive shaft, each blade is pivotally fixed to the hub and pivotal about a respective blade pivot axis which extends radially from the hub, the blades are mechanically interconnected to transfer pivotal movement of each blade to all other blades and wherein the hub exhibits an axially extending exhaust channel for transportation of exhaust gases.

According to an embodiment of the propeller of the second aspect the exhaust channel is annular and arranged concentrically around the central bore of the hub.

According to a third aspect the present disclosure provides a self-adjusting variable pitch propeller for marine use which propeller comprises a central hub with an axial propeller centre line defining the rotational axis of the propeller and a plurality of blades extending radially from the hub, wherein the hub exhibits a central bore arranged to receive a rotating drive shaft, each blade is pivotally fixed to the hub and pivotal about a respective blade pivot axis which extends radially from the hub, the blades are mechanically interconnected to transfer pivotal movement of each blade to all other blades and wherein the hub comprises at least two segments which are mutually fixed one after the other in the axial direction of the propeller and wherein the blades are fixed to the hub at respective recesses formed in the hub at the junction between two segments.

Further objects and advantages of the self-adjusting variable pitch propeller according to the first, second and third aspects will be apparent from the following description of exemplifying embodiments and from the appended claims.

The self-adjusting variable pitch propeller <NUM> shown in <FIG> is intended for marine use at a vessel or a boat having a power plant in the form of an inboard or outboard combustion engine. The propeller comprises a hub <NUM> and four blades <NUM> which are equally distributed about the circumference of the hub <NUM>. In alternative, not shown embodiments, the propeller may however comprise another number of plural blades. Typically, the propeller may comprise <NUM>-<NUM> and preferably <NUM>-<NUM> blades. The hub <NUM> is arranged to be fixed to an output shaft S (<FIG>) of the engine and has an axial propeller centre line C which defines the rotational axis of the propeller <NUM>. During forward drive of the vessel, the propeller <NUM> rotates about the centre line C in the clockwise rotational direction R as seen in <FIG>.

Each blade <NUM> is fixed to a blade root <NUM> and extends radially, with respect to the axial centre line C, from the hub <NUM> and is pivotally fixed to the hub such that each blade <NUM> is pivotal about a respective pivot axis P (<FIG>) which extends radially through the blade <NUM> and the blade root <NUM> with respect to the centre line C. The blades <NUM> are essentially mutually identical and the following description of one blade <NUM> applies equally to all four blades <NUM>. Each blade <NUM> exhibits a leading edge <NUM> and a trailing edge <NUM>. The leading edge <NUM> faces in the rotational direction R during forward drive of the vessel. Each blade <NUM> further exhibits a suction side <NUM> exhibiting a suction side area and a pressure side <NUM> exhibiting a pressure side area, both of which extends between the leading edge <NUM> and the trailing edge <NUM>. During forward drive, the suction side <NUM> is arranged generally in front of the pressure side <NUM> with respect to the forward movement of the vessel. The blade <NUM> exhibits a three-dimensional double curved geometry in a manner such that the suction side <NUM> is convex and the pressure side <NUM> is concave. This results in that the suction side <NUM> area is larger than the pressure side <NUM> area. In the shown example the blade <NUM> and the blade root are formed integrally as a single piece component. The blade and blade root may however also be formed as different components which are fixedly connected.

Each blade further comprises a bladelet <NUM> or vortex reducer which is arranged at the blade tip <NUM> being positioned at the radially outer end of the blade <NUM>. The bladelet <NUM> is formed as a protrusion or bead which protrudes from the blade tip <NUM> edge towards the suction side <NUM> and reduces water flow from the suction side to the pressure side <NUM>, over the blade tip to thereby reduce cavitation at the blade tip <NUM>. The length of the bladelet <NUM> is preferably approx. <NUM>-<NUM>% of the total radial length of the blade <NUM>. The blade <NUM> further comprises a blade diffuser <NUM> or separation delayer which is arranged at the trailing edge <NUM> and extends from the blade tip <NUM> inwardly, approx. half the way towards the hub <NUM>. The blade diffuser <NUM> comprises a portion of the blade in the region adjacent the trailing edge, which portion is bent or curved towards the suction side <NUM>. The length of the blade diffuser in the rotational direction R of the propeller is approx. <NUM>-<NUM>% of the distance between the leading <NUM> and trailing <NUM> edge at the blade diffuser. The blade diffuser <NUM> reduces the water resistance experienced by the propeller to thereby increase the efficiency and reduce fuel consumption. The blade further exhibits a through opening <NUM> which is arranged at the radially inner half of the blade. The area of the through opening <NUM> constitutes approx. <NUM>% of the radially inner half of the suction side <NUM> area. The through opening <NUM> results in that the active suction side area and pressure side area is moved radially outwards towards the peripheral portion of the blade. Since this portion exhibits a higher rotational speed than the radial inner portion of the blade, the through opening <NUM> increases the efficiency and, in particular, increases acceleration and starting torque.

The hub <NUM> will now be explained in further detail with reference mainly to <FIG> and <FIG>. <FIG> is an exploded view of the hub <NUM> and <FIG> illustrates the hub <NUM> assembled but with some outer parts removed. The hub <NUM> comprises four axial segments <NUM>, <NUM>, <NUM>, <NUM> which are arranged one after the other in the axial direction of the centre line C. The segments comprise a front segment <NUM>, a first intermediate segment <NUM>, a second intermediate section <NUM> and a rear segment <NUM>. The segments are fixedly connected to each other by means of axially extending fastening screws and bots as shown in <FIG>. Each section comprises a tubular inner sleeve portion <NUM>, <NUM>, <NUM>, <NUM> which exhibits a central splined bore portion <NUM>, <NUM>, <NUM>. The inner sleeve portions together form a central sleeve <NUM> of the hub <NUM> and the bore portions together form a central splined bore <NUM> of the hub <NUM> which bore <NUM> receives the rotating drive shaft S of the engine.

Each segment <NUM>, <NUM>, <NUM>, <NUM> further comprises an outer sleeve portion <NUM>, <NUM>, <NUM>, <NUM> which is arranged concentrically with and outside the respective inner sleeve portion <NUM>, <NUM>, <NUM>, <NUM> and which together form a peripheral sleeve <NUM> of the hub <NUM>. By this means an annular space is formed between peripheral sleeve <NUM> and the central sleeve <NUM>, which space constitutes an exhaust channel <NUM> extending axially through the hub <NUM>. When the propeller <NUM> is fixed on the output shaft S of the engine, the front end of the exhaust channel <NUM>, which front end is formed by the front segment <NUM> is in communication with an exhaust outlet of the engine such that exhaust gases from the engine passes through the exhaust channel <NUM> of the hub <NUM>.

At each segment <NUM>, <NUM>, <NUM>, <NUM>, the inner sleeve portion <NUM>, <NUM>, <NUM>, <NUM> is connected to the respective outer sleeve portion <NUM>, <NUM>, <NUM>, <NUM> by means of spoke members 14a, 24a, 34a, 44a-d. In the shown example each segment <NUM>, <NUM>, <NUM>, <NUM> comprises four helical spoke members as best illustrated in <FIG> by the four helical spoke members 44a-d of the rear segment <NUM>. Each spoke member forms an axial section of a turbine blade 7a-d, such that when the segments are assembled, four turbine blades 7a-d are formed in the exhaust channel. In <FIG>, this is best represented by the spoke members 14a, 24a, 34a, 44a which together form the turbine blade 7a. In this manner, the four turbine blades 7a-d together form part of a turbine <NUM>. Upon rotation of the propeller <NUM>, the turbine <NUM> greatly decreases the resistance for the exhaust gases to leave the engine, thereby increasing the efficiency of the engine, increasing acceleration and reducing the fuel consumption.

The hub <NUM> further comprises a gear arrangement <NUM> which is best seen in <FIG> and <FIG>. In these figures the blade has been removed for increased visibility such that only the blade root <NUM> is shown. Further, in <FIG> only one of the four blade roots is shown. The blade root <NUM> is journaled to the outer sleeve <NUM> of the hub <NUM>. For this purpose, the first <NUM> and second <NUM> intermediate sections each exhibits four semi-circular openings 25a-b, 35a-b arranged through the respective outer sleeve portion <NUM>, <NUM>, and mutually facing each other in pairs 25a-35a and 25b-35b. Each blade root <NUM> has a cylindrical portion, the diameter of which corresponds to the diameter of cylindrical opening defined by each pair 25a-35a, 25b-35b of semi-circular openings, such that the blade root <NUM> and the blade <NUM> may pivot about the pivot axis P (<FIG>) relative to the hub <NUM>. Each blade root <NUM> comprises two opposing radially protruding stop members <NUM> each of which is received in a corresponding respective recess <NUM> formed in the outer sleeve portions <NUM>, <NUM> with a clearance. By this means the pivotal movement in both pivotal directions of the blade <NUM> and blade root <NUM> is limited to a maximum pivotal angle defined by the clearance. Preferably the clearance should be selected such as to allow pivoting of the blade <NUM> between a minimum pitch of <NUM>,<NUM> (<NUM> inch) and a maximum pitch of <NUM>,<NUM> (<NUM> inch). In the shown example this corresponds to a maximum pivotal angle of approx.

The gear arrangement comprises interconnecting members <NUM>, <NUM> arranged to mechanically interconnect the blade roots <NUM> for synchronising the pivotal movement of the blades <NUM>. In the shown example, the gear arrangement comprises two different types of interconnecting members <NUM>, <NUM>.

A first type comprises two ring-shaped members <NUM> each exhibiting primary second gear teeth 71a which mesh with primary first gear teeth <NUM> arranged on the stop members <NUM> of all four blade roots <NUM> (only one shown in <FIG>).

A second type of interconnecting members comprises four bevelled cog wheels <NUM> with secondary second gear teeth 72a which meshes with secondary first gear teeth <NUM> arranged at the blade root <NUM>. The secondary second gear teeth <NUM> of each cog wheel <NUM> meshes with the secondary first gear teeth <NUM> of two neighbouring or adjacent blade roots.

Both the first <NUM> and the second <NUM> type of interconnecting members assures that all four blades <NUM> are interconnected and synchronized such that all blades assume the same pitch at all instances. In the shown example, the propeller is provided with both the first and the second type of interconnecting members. In many cases however it suffices to provide the propeller with either the first type or the second type. In cases where the first type of interconnecting members is used the gear arrangement may comprise only one such interconnecting member <NUM>. However, it may be preferable to arrange two such interconnecting members <NUM> for symmetry reasons and for avoiding skewing of the blade root and the interconnecting member caused by non-symmetrical load. The type and number of interconnecting members may be selected depending on i. the power output of the engine, the size of the propeller and the hub and the type of vessel to be propelled by the propeller.

As best illustrated in <FIG> and <FIG> the suction side area and the pressure side area of the blades are arranged with in a specific manner with respect to the pivot axis P of the blades. <FIG> is a side view corresponding to the view in <FIG> illustrating an exemplifying blade <NUM>' (without the blade root) according to a second embodiment. <FIG> shows the pressure side of the blade <NUM>' <FIG> is a plan view from the front of the propeller showing the suction side of the propeller <NUM>' shown in <FIG>. In both <FIG> and <FIG>, the direction of the propeller centre line C has been schematically indicated for reference purposes.

As in the example shown in <FIG>, the blade comprises a leading edge <NUM>', a trailing edge <NUM>' and a blade tip <NUM>'. The pressure side <NUM>' shown in <FIG> and the suction side <NUM>' shown in <FIG> both extend between the leading edge <NUM>', the trailing edge <NUM>', the blade tip <NUM>' and the not shown blade root arranged proximal to the centre line C. The blade <NUM>' is pivotal about the pivot axis P as described above with reference to <FIG>. Both the pressure side <NUM>' and the suction side <NUM>' surfaces are double curved in such a manner that the suction side area is somewhat greater than the pressure side area. The pivot axis P extends through the blade <NUM>' and is arranged such that a majority i.e. more than <NUM>% of both the suction side area <NUM>' and the pressure side area <NUM>' is arranged at a trailing portion of the blade <NUM>' i.e. between the pivot axis P and the trailing edge <NUM>'. In the shown example approx. <NUM>,<NUM> % of the suction side area and <NUM>,<NUM>% of the pressure side area is arranged between the pivot axis P and the trailing edge <NUM>'. It has proven especially advantageous if more than half and up to <NUM>% of the suction side area and more than half and up to <NUM>% of the pressure side area is arranged between the pivot axis P and the trailing edge <NUM>'.

With such arrangements of the suction side and pressure side areas in relation to the pivot axis and the trailing edge it has been found that the blades automatically will assume an optional or at least advantageous pitch over the entire rpm interval for the propeller and that such advantageous automatic adjustment of the pitch occurs irrespective of the vessel's speed through the water, the torque applied to the propeller and within a large interval of varying diameters of the propeller. By achieving such advantageous automatic pitch adjustment, several advantages in the form of increased acceleration, higher top speed, lower energy consumption and better manoeuvrability of the vessel are gained. With the design of the propeller disclosed herein these advantages are readily achieved in a simple manner grace to the comparatively simple construction of the propeller comprising inly a low number of constituent components. The design and especially the modular construction comprising axially aligned segments of the hub also allows for easy assembling and disassembling of the propeller and thereby that damaged components such as the blades readily may be replaced.

Claim 1:
A self-adjusting variable pitch propeller (<NUM>) for marine use, comprising a central hub (<NUM>) with an axial propeller centre line (C) defining the rotational axis of the propeller and a plurality of blades (<NUM>, <NUM>') extending radially from the hub, wherein
- the hub (<NUM>) exhibits a central bore (<NUM>) arranged to receive a rotating drive shaft (S),
- each blade (<NUM>, <NUM>') is pivotally fixed to the hub (<NUM>) and pivotal about a respective blade pivot axis (P) which extends radially from the hub (<NUM>) through the respective blade (<NUM>, <NUM>'),
- each blade (<NUM>, <NUM>') exhibits a leading edge (<NUM>, <NUM>'), a trailing edge (<NUM>, <NUM>'), a pressure side (<NUM>, <NUM>') exhibiting a pressure side area and a suction side (<NUM>, <NUM>') exhibiting a suction side area,
characterized in that
- the blades (<NUM>) are mechanically interconnected to freely transfer pivotal movement of each blade to all other blades and wherein
- the pivotal axis (P) of each blade (<NUM>, <NUM>') is positioned such that > <NUM>% of the suction side (<NUM>, <NUM>') area and of the pressure side (<NUM>, <NUM>') area is arranged between the trailing edge (<NUM>, <NUM>') and the pivotal axis (P) of the respective blade (<NUM>, <NUM>').