WO2013034972A1

WO2013034972A1 - Nautical propeller with automatic adjustment of blades pitch in relation to its rotation speed

Info

Publication number: WO2013034972A1
Application number: PCT/IB2012/001728
Authority: WO
Inventors: Massimiliano Bianchi
Original assignee: Max Prop S.R.L.
Priority date: 2011-09-07
Filing date: 2012-09-07
Publication date: 2013-03-14
Also published as: SMP201400039B; SMAP201400039A; WO2013034946A1

Abstract

There is described a propeller (1) of the type comprising an external cylindrical casing (2) coupled directly or indirectly to an engine shaft in a manner rotatable about the axis (X) of the propeller, and at least one blade (3) provided with at least one fluid dynamic surface (4) constrained to a related blade shaft (5), which is in turn constrained to said external cylindrical casing (2) to be driven in rotation about the axis of the propeller. The blade shaft (5) has its axis (Y) which extends in a direction incident to the axis (X) of the propeller and the at least one fluid dynamic surface is driven by the related blade shaft in rotation about the axis of the propeller. The propeller is characterized by comprising at least one guide constraint (11, 12) between the at least one fluid dynamic surface (4) and the respective blade shaft (5), said at least one guide constraint comprising at least one first section (11a) and at least one second section (11b). The at least one first section (11a) is shaped to allow the translation or the roto-translation of the fluid dynamic surface (4) relative to the blade shaft (5), and vice versa, and the at least one second section (11b) is shaped to allow the roto-translation of the fluid dynamic surface (4) relative to the blade shaft (5), and vice versa.

Description

"Nautical propeller with automatic adjustment of blades pitch in relation to its rotation speed"

A "k "k "k FIELD OF THE INVENTION

The present invention relates to a propeller, preferably for nautical use, wherein the variation of the fluid dynamic pitch of the propeller blades takes place automatically in relation to the rotation speed of the propeller.

More in detail, the propeller according to the present invention allows, as a function of the rotation speed of the propeller imparted by the engine, and therefore as a function of the intensity of the centrifugal force acting on the blades, the automatic variation of the fluid dynamic pitch thereof, i.e. the angle of incidence of the fluid dynamic surface of the blades relative to the fluid that strikes them.

BACKGROUND ART

It is known in the art that modification of the fluid dynamic pitch of the blades to adapt to the operating conditions of the propeller is very advantageous and allows high output to be obtained.

For this reason, propellers have been designed that allow continuous variation of the fluid dynamic pitch as a function of the operating conditions of the propeller, and in particular of the forces acting on the fluid dynamic surfaces of the blades. Generally, these propellers comprise a cylindrical propeller casing, on which the blades are pivoted, by means of a related blade shaft, according to a direction transverse to the axis of the same propeller casing, or more in general perpendicular to the drive axis of the propeller, and an engine shaft, coupled coaxially to the propeller casing.

The propeller is also provided with means for transmitting rotary motion from the shaft to the propeller casing, and with a kinematic mechanism for adjusting the rotary motion of each blade shaft about its pivoting axis to the propeller casing, preferably adapted to transform the rotary motion of the engine shaft into a rotary motion of each blade shaft, and therefore of the fluid dynamic surface of the blade integral therewith, about the pivoting axis of the blade shaft to the cylindrical propeller casing. In order to allow operation of the aforesaid kinematic mechanism for transforming rotation of the engine shaft into rotation of the blades, the motion transmission means provide for idle rotation of the engine shaft relative to the propeller casing at least for a predefined angular interval. Idle rotation of the engine shaft in this angular interval, relative to the propeller casing, causes, due to the aforesaid kinematic mechanism for adjustment/transformation, relative rotation of the blade shafts, and therefore of the blades integral therewith, relative to the propeller casing, with consequent modification of their angle of incidence relative to the fluid and therefore modification of the fluid dynamic pitch.

A propeller of this type is described in the patent WO 2008/075187, by Max Prop S.r.l., in which relative rotation of the engine shaft relative to the propeller casing is adjusted by an elastic element interposed therebetween, which allows continuous pitch adjustment during operation.

In particular, the elastic element allows the blades to be arranged at the optimal pitch during operation, balancing the forces acting on the propeller, mainly comprising the drive torque generated by the engine and the drag torque, until reaching a position of balance. The blades can thus be arranged at various fluid dynamic pitches following the relative rotation in said angular interval of rotation of the cylindrical propeller casing relative to the engine shaft, and vice versa.

At the two ends of the angular interval of relative rotation of the engine shaft relative to the propeller casing, the blades will be arranged at two fluid dynamic pitches, i.e.

"limit" pitches, which are established in the design stage.

It must be noted that, in propellers of the type described above, variation of the pitch is obviously linked to the amplitude of the angular interval of relative rotation of the engine shaft relative to the cylindrical propeller casing, and vice versa. In fact the rotation angle determines, at the ends thereof, the minimum and maximum "limit" pitches that can be reached by the blades.

Propellers are also known in the art of the kind wherein the variation of the fluid dynamic pitch occurs as a function of its rotation speed, and therefore as function of the centrifugal force acting upon it, thanks to a weight that is axially movable, under the action of centrifugal force, whose motion is converted into rotation of the blade by means of a helical type coupling between the weight and the blade.

A propeller of this type is described in the document US2,416,541 in which more blade shafts are mounted in a rotatable manner (about their own longitudinal axis) to a corresponding portion of the propeller casing. A weight is installed within each blade shaft that can translate along the longitudinal axis of the blade shaft but cannot rotate relative to it. The weight is coupled by a helical connection to the blade shaft, in fact, the outer surface of the weight is provided with helical grooves adapted to cooperate with protruding guides, which are also helical, formed on the inner surface of the blade shaft chamber wherein the weight is installed.

In doing so, the translation movement of the weight along the longitudinal blade shaft, due to centrifugal force, is converted by the helical connection in rotation motion of the blade shaft, and therefore of the blade constrained thereto, to determine the modification of the fluid dynamic pitch.

The document US 2,547,037 describes a similar propeller wherein each blade is provided with an inner chamber inside which an adjusting device is placed which comprises a cylindrical body provided on its surface of guides in correspondence of which a weight is movable. More in detail, the weight is arranged within the cylindrical body in such a way to be slidable under the action of the centrifugal force due to the rotation of the propeller. In fact, the weight is provided with two projecting fins intended to cooperate with the helical guides of the cylindrical body in order to determine the rotation of the weight during its translation movement within the cylindrical body. The rotational movement of the weight, during its axial sliding, is transmitted to the blade, in fact, the weight is provided with projecting bearings which cooperate with the rectilinear guides arranged on the inner surface of the inner chamber of the blade. In addition, a spring is arranged to counteract axial movement of the weight towards the outside, due to centrifugal force.

In propellers according to the documents US 2,416,541 and US 2,547,037, briefly described above, there is a weight, or more in general an axially movable element (relative to the pivoting axis of the blade to the propeller casing), under the action of the centrifugal force, the axial translation movement of which is converted to the rotational motion of the blade by means of a coupling, preferably of the helical type. The presence of the movable weight inevitably complicates the construction and maintenance process of the propeller that will be subjected to high wear and risk of malfunction.

Even in the propeller described in document FR 733739 the axial translation movement of the movable element (I) determines the rotation of the blade holder element (E), and therefore of the blade coupled thereto. Basically, the coupling of the helical guides (N and L) of the blade holder element (E) with those (O and P) of the movable element (I) transform the translational movement of the movable element (I), along the axis (F-G), in the rotation movement, about the same axis, of the blade holder element (E), and then of the blade constrained thereto.

Whereas, in the propeller described in document FR 1435382 elements or movable weights are not present, but it is the blade itself which, under the action of the centrifugal force acting on it changes its fluid dynamic pitch. More in detail, the propeller comprises tubular support elements, adapted to support the blades, which are provided with a guide intended to cooperate with a projecting element arranged on the underside of the blade. During the rotation of the propeller, the centrifugal force causes the movement of the elements projecting inside the guides, resulting in the modification of the fluid dynamic pitch of the blade.

In propellers described above, and in particular in that according to FR 1435382 there is the drawback that even at low propeller rotation speeds, for example immediately after the cranking, or during maneuvers, and in general in the conditions of use of the engine at a low, or minimum, number of revolutions, the modification of the fluid dynamic pitch of the blades is still determined.

Such modification, in the conditions of use described above, adversely affects the efficiency of the propeller and boat performance.

In fact, in propellers known in the art, in some cases, variation of the fluid dynamic pitch of the blades does not allow an "optimum" pitch suitable for the operating conditions to be reached, and therefore it is unable to ensure that the desired efficiency will be obtained in given operating conditions.

In general, it is possible that, in given operating conditions, the engine will be unable to operate the propeller correctly, resulting in unsatisfactory performance and output. These drawbacks can occur in the case in which the propeller to be coupled to the engine is not chosen correctly, or in the case in which, for various reasons, it is necessary to install a propeller having characteristics related to variation of pitch and limit pitches obtainable which are not suitable for the characteristics of power, torque produced and rotation speed of the engine on which it is installed.

In fact, with prior art propellers, in order to reach an "optimal" pitch suitable for forward movement, for example in cruising conditions, the initial fluid dynamic pitch must be very high.

This characteristic entails that an efficient operating condition of the propeller with high output can only be reached following installation thereof on an engine capable of producing high torque values at low rotation speeds (low number of revolutions). In the case in which the engine on which the propeller is installed produces low torque values at low rotation speeds, this causes problems in manoeuvring the boat, making it impossible to perform sudden and quick movements.

These drawbacks are marked in the case of using high powered engines which, unlike engines of more limited dimensions, produce low torque values at low rotation speeds and have relatively steep characteristic curves (which, as known, describe the ratio between torque and rotation speed).

To use prior art propellers with high power engines, and in general with engines that produce low torque values at low rotation speeds, it would be desirable to be able to decrease the fluid dynamic pitch, in such a manner as to be able to arrange the blades at a small initial pitch.

However, it must be noted that, starting from a too small fluid dynamic pitch in order to allow rapid starting and manoeuvring of the boat, it would subsequently not be possible to reach the "optimal pitch" suitable for forward movement.

Consequently, when choosing the propeller, the user of the boat will be obliged to opt, according to specific needs, for characteristics of the propeller more suitable for forward movement, or for characteristics more suitable for start-up with advantages concerning the ease with which the boat is manoeuvred.

For these reasons, in some operating conditions of the propeller, and in particular cases of coupling with some engines, above all with high powers, or which in general produce low torque values at low rotation speeds, there is the need to provide an alternative method of varying the fluid dynamic pitch of the propeller blades, or to provide a wider pitch adjustment interval, between minimum pitch and maximum pitch.

The object of the present invention is to overcome the problems of prior art propellers, discussed briefly above, and to provide a propeller in which adjustment of the fluid dynamic pitch of the blades takes place independently from rotation of the blade shaft relative to the cylindrical propeller casing.

In particular, it is an object of the present invention to provide a propeller wherein the automatic variation of the pitch may take place only when a certain rotation speed of the propeller is overcome, so that below said rotation speed value the fluid dynamic pitch of the blades does not vary and remains substantially fixed at a predetermined value.

Another object of the present invention is to provide a propeller provided with an independent pitch adjustment system, which can be used in alternative or in addition to the pitch adjustment system which provides for rotation of the blade shaft about its axis of pivoting to the propeller casing.

SUMMARY OF THE INVENTION

These and other objects are achieved by a propeller according to claim 1 , while further aspects and characteristics thereof are presented in the dependent claims.

The propeller according to the present invention is of the type comprising an external cylindrical casing coupled directly or indirectly to an engine shaft in a manner rotatable about the axis of the propeller, and at least one blade provided with at least one fluid dynamic surface constrained to a related blade shaft, which is in turn constrained to said external cylindrical casing to be driven in rotation about the axis of the propeller. It must be noted that the axis of the blade shaft extends in a direction incident to the axis of the propeller and that at least one fluid dynamic surface is driven, by the related blade shaft, in rotation about the axis of the propeller.

The propeller is characterized by comprising at least one guide constraint placed between the at least one fluid dynamic surface and the relative blade shaft, said at least one guide constraint having at least a first section and at least a second section. The at least one first section is shaped to allow the translation or the roto-translation of the fluid dynamic surface relative to the blade shaft, and vice versa, and the at least one second section is shaped to allow the roto-translation of the fluid dynamic surface relative to the blade shaft, and vice versa.

The translation motion (in the case allowed by the first section of the guide constraint) and roto-translation motion of the fluid dynamic surface relative to the related blade shaft is caused by the centrifugal force acting on this blade, in turn caused by the rotation of the propeller, and in particular by the rotation of the cylindrical casing, which is imparted by the engine shaft to which it is coupled in rotation.

Obviously it is clear that the translation motion occurs along a radial direction, relative to the rotation axis X of the propeller.

As will be clear to one skilled in the art, the rotation of the fluid dynamic surface relative to the blade shaft, about the axis of the same blade shaft, with the simultaneous translation along the axis of the blade shaft, determines the modification of the angle of incidence with the fluid, and thus the modification of the fluid dynamic pitch.

Advantageously, in the propeller according to the present invention, the variation of the fluid dynamic pitch thus takes place in relation to the rotation speed of the engine, and therefore in relation to the rotation speed of the propeller coupled thereto in rotation.

In fact, as will be seen in more detail below, the second section of the guide constraint is shaped to allow the roto-translation of the fluid dynamic surface relative to the blade shaft, determining consequently the rotation from a first fluid dynamic pitch to a second fluid dynamic pitch.

Furthermore, according to an aspect of the present invention, the guide constraint between the fluid dynamic surface and the blade shaft in the first section shaped for the translation of the fluid dynamic surface does not determine the pitch modification, allowing to maintain unchanged the fluid dynamic pitch at a predetermined value for low values of rotation speed of the propeller, and in any case until reaching a preset value of rotation speed of the propeller. In fact, according to a possible embodiment, the guide constraint between the fluid dynamic surface and the blade shaft is such to initially allow only the translation of the fluid dynamic surface (in the first section of the guide constraint), keeping unchanged the fluid dynamic pitch up to achieve a determined value of rotation speed (and therefore the intensity of the centrifugal force acting on the propeller). Upon reaching this value of rotation speed, the guide constraint between the fluid dynamic surface and the blade shaft allows the modification of the fluid dynamic pitch by the roto-translation of the fluid dynamic surface relative to the blade shaft (in the second section of the guide constraint).

Whereas, in the case in which the first section of the guide constraint is shaped to allow the roto-translation of the fluid dynamic surface, it will allow, as better explained hereinafter, a very limited rotation of the fluid dynamic surface that determines a very limited modification of the fluid dynamic pitch of the blade. It follows that even in the possible embodiment wherein the first section of the guide constraint allows the roto-translation of the fluid dynamic surface, it will be determined a minimum and therefore insignificant variation of the fluid dynamic pitch until the reaching of a determined rotation speed value (and therefore of the centrifugal force intensity acting on the propeller). Upon reaching said rotation speed value, the second section of the guide constraint between the fluid dynamic surface and the blade shaft allows the modification of the fluid dynamic pitch by way of the roto-translation of the fluid dynamic surface relative to the blade shaft (in the second section of the guide constraint). In fact, in the case wherein the first section of the guide constraint is shaped to allow the roto-translation of the fluid dynamic surface relative to the blade shaft, and vice versa, the rotation allowed by the first section is less than the rotation allowed by the second section, at equal translation.

It follows that, in both operation modes, the user of the boat can choose a propeller with characteristics suitable for forward movement even if the motor produces low torque values for low rotation speeds, thus overcoming the problems reported in the use of prior art propellers, in fact, up to the achievement of a determined rotation speed value of the propeller the pitch will remain unchanged, or substantially unchanged (thanks to the first section of the guide constraint) and subsequently may vary within the increase of the rotation speed of the propeller by way of the second section of the guide constraint.

According to a possible embodiment the at least one guide constraint comprises at least one guide surface and at least one slider integral respectively with the blade shaft and with the fluid dynamic surface, or vice versa. The guide surface comprises at least a first section shaped to allow the translation or the roto-translation of the fluid dynamic surface relative to the blade shaft, and vice versa, and at least a second section shaped to allow the roto-translation of the fluid dynamic surface relative to the blade shaft, and vice versa. Preferably, the first section of the guide precedes the second section of the same along the direction of movement, towards the outside, imposed by the centrifugal force. In other words, the first section is in a position close to the axis (X) of the propeller and the second section is in the distal position from the axis (X) of the propeller.

Furthermore, preferably the first section and the second section of the guide are in succession and the second end (final) of the first section corresponds to the first end (start) of the second section of the guide.

According to one aspect of the present invention, the first section of the guide comprises a first and a second end, and the slider is located in correspondence of the first and second end of the first section of the guide, respectively when the fluid dynamic surface is in the initial position and in an intermediate position.

Furthermore, according to an aspect of the present invention, the second section of the guide comprises a first and a second ends, and the slider is located in correspondence of the first and second ends of the second section of the guide, respectively when the fluid dynamic surface is in the intermediate position and in the final position.

In particular, the initial position of the fluid dynamic surface along the blade shaft is in position proximal to the axis of the propeller, while the final position of the fluid dynamic surface along the blade shaft is in distal position from the axis of the propeller, so that the centrifugal force acting on the blade determines automatic shifting from the initial position to the final position, shifting to the intermediate position, as a result of the motion of the fluid dynamic surface relative to the blade shaft in the first and second section of the guide.

In other words, the first section and the second section of the guide are in succession to one another and the end of the first section corresponds to the beginning of the second section of the guide.

According to a possible embodiment the at least one first section is parallel to the axis (Y) of the blade shaft, and the at least one second section is inclined relative to the axis (Y) of the blade shaft.

In doing so, due to the centrifugal force acting on the blade, it will be movable between an initial position and an intermediate position, by determining the single motion of the fluid dynamic surface relative to the blade shaft, by the sliding of the slider in the first section of the guide parallel to the axis Y. The translation motion only does not determine the modification of the fluid dynamic pitch that will remain unchanged until reaching a certain rotation speed of the propeller (centrifugal force intensity). In fact, from the intermediate position wherein the fluid dynamic surface is arranged at a first fluid dynamic pitch, which is the initial one since in the translation movement from the initial position to the intermediate position, the rotation of the fluid dynamic surface has not intervened and likewise modification of the fluid dynamic pitch, it will roto-translate relative to the blade shaft, in the second section of the guide inclined relative to the axis Y of the blade shaft, until reaching a final position wherein the fluid dynamic surface affects the fluid with a second fluid dynamic pitch.

According to a further possible embodiment the at least one first section is inclined relative to the axis (Y) of the blade shaft and the at least one second section is inclined relative to the axis (Y) of the blade shaft. The inclination (al) of the at least a first section relative to the axis (Y) of the blade shaft is less than the inclination (al) of the at least a second section relative to the axis (Y) of the blade shaft.

In doing so, by way of the centrifugal force acting on the blade, it will be movable between an initial position and an intermediate position, causing the translation and at the same time a limited rotation of the fluid dynamic surface relative to the blade shaft, by the slide of the slider in the first section of the guide parallel to the axis Y. Such motion determines a limited modification of the fluid dynamic pitch until it reaches a certain rotation speed of the propeller (intensity of centrifugal force). In fact, from the intermediate position wherein the fluid dynamic surface is arranged at a fluid dynamic pitch, which corresponds substantially to the initial one since in the translation motion from the initial to the intermediate position in the first section of the guide intervenes a limited rotation of the fluid dynamic surface and therefore a limited modification of the fluid dynamic pitch, it will roto-traslate relative to the blade shaft, in the second section of the guide inclined relative to the axis Y of the blade shaft, until reaching a final position wherein the fluid dynamic surface affects the fluid with a second fluid-dynamic pitch.

It should be immediately noted that the inclination relative to the axis (Y) of the blade shaft of the second section of the guide constraint, and optionally also of its first section, is preferably made on the outer cylindrical surface of the blade shaft itself resulting in the formation of a section (and of a constraint) of "helical" type. In other words, the inclination of the first and second section of the guide constraint allows the roto-translation movement of the fluid dynamic surface of the blade relative to the blade shaft, after composition of a rotation motion about, and a translation motion along the axis of the blade shaft.

As is known, a helical trajectory is given by the composition of a rectilinear motion parallel to a straight line, and by the rotation about this straight line. Obviously, besides the guide along which the related slider slides, other means known in the art which allow shifting along an at least partly helical trajectory can be used to constrain in roto-translation the fluid dynamic surface of the blade to the blade shaft. The propeller according to the present invention also comprises elastic means to adjust the motion of the at least one fluid dynamic surface relative to the blade shaft, and vice versa.

More in detail, the elastic means allow the translation, or the translation with limited rotation (depending on the two possible embodiments of the first section of the guide constraint) of the fluid dynamic surface along the respective blade shaft, from the initial position to the intermediate position, only after exceeding a predetermined rotation speed of the cylindrical propeller casing about the propeller axis.

Similarly, the elastic means allow the roto-translation of the fluid dynamic surface along the respective blade shaft in the second section of the guide constraint, from the intermediate position to the final position, after exceeding a predetermined rotation speed of the propeller cylindrical body about the propeller axis.

Obviously, according to possible embodiments, the elastic means may be suitably chosen so as to control in a common or separate way, the movement of the fluid dynamic surface between the original position and the intermediate position in the first section of the guide constraint and its roto-translation between the intermediate position and the final position in the second section of the guide constraint.

Furthermore, the propeller can only be provided with elastic means adapted to control only the motion of the fluid dynamic surface between the initial position and the intermediate position, in the first section, or to control only the roto-translation motion between the intermediate position and the final position in the second section. The elastic means, which according to a possible embodiment can comprise one or more springs, oppose, in a controlled manner the translation and/or roto-translation of the fluid dynamic surface relative to the related blade shaft, in relation to the rotation speed of said cylindrical propeller casing.

This solution, as will be clear to those skilled in the art, allows the fluid dynamic surface of the blade to firstly be induced only to translate or roto-translate with a limited rotation component (depending on the two possible embodiments of the first section), while keeping unchanged, or substantially unchanged, the fluid dynamic pitch, and subsequently be induced to rotate and translate radially about/along the axis of the blade shaft (in the second section) - when the engine shaft and the cylindrical propeller casing is made to rotate - even if this motion is opposed in a controlled manner by the elastic means, i.e. only for certain rotation values of the engine shaft, and therefore only for certain intensities of centrifugal force acting on the blade.

In this manner, the fluid dynamic surface can shift from the initial position to the intermediate position substantially without modification of the fluid dynamic pitch as a result of only the translation motion relative to the blade shaft or roto-translation with a very limited rotation component (in the two embodiments of the first section), and from the intermediate position to the final position, allowing the passage from the first (predetermined) fluid dynamic pitch toward the second fluid dynamic pitch, following roto-translation motion about the blade shaft in the second section, only when it overcomes the resistance to radial rotation and translation thereof exerted by the elastic means, i.e. only when the engine shaft, and therefore the cylindrical propeller casing coupled in rotation thereto, has reached an angular speed such as to cause the centrifugal force, to which the fluid dynamic surface is subjected, would exceed the force exerted by the elastic means. The elastic means can be arranged in such a manner as to be interposed between at least one fluid dynamic surface and the related blade shaft and/or housed at least partially inside the blade shaft.

According to some possible embodiments, the elastic means are housed in at least one seat located between said fluid dynamic surface of the blade and the outer surface of the respective blade shaft.

Furthermore, it will be clear that the elastic means are compressed as a result of the translation and roto-translation of the fluid dynamic surface along the blade shaft, from the initial position to the final position, passing through said intermediate position.

According to a possible embodiment, the propeller also comprises means to stop translation and/or roto-translation of the fluid dynamic surface relative to the related blade shaft, which are preferably selected from limit stops, rings, pins, either fixed or movable in specific seats.

The stop means allow translation of the fluid dynamic surface along the axis of the related blade shaft to be limited, modifying the reaching of the initial position and/or final position and/or intermediate position, and consequently determining a modification of the corresponding first and second fluid dynamic pitch reached by the fluid dynamic surface.

Advantageously, by means of the propeller according to the present invention it is possible to keep unchanged, or substantially unchanged, the fluid dynamic pitch to a first preset value, until the reaching of a certain rotation speed of the propeller, for then automatically vary the fluid dynamic pitch, with increasing rotation speed of the engine, and then of the centrifugal force acting on the blades, on a second fluid dynamic pitch. The fact that the fluid dynamic surface is constrained in a translatable or roto-translatable manner in the first section of the guide constraint and roto- translatable in the second section of the guide constraint, to the related blade shaft, and that therefore there is at least one relative movement between the fluid dynamic surface of the propeller and the related blade shaft, constitutes a separate adjustment device, which can be used in addition or in alternative to prior art automatic pitch adjustment systems, such as the type described in the patent WO 2008/075187, which provides for rotation of the blade shaft relative to the cylindrical propeller casing about its axis of pivoting to the cylindrical propeller casing.

In fact, in the case in which the blade shafts of the propeller are pivoted to the cylindrical casing in such a manner as to be rotatable about its axis, and a kinematic mechanism is also provided coupled to the engine shaft, and/or to the cylindrical propeller casing, and to the blade shafts, for adjustment of the rotary motion of the blade shaft relative to the cylindrical propeller casing about the axis of the blade shaft, the present pitch adjustment system by means of the translation and of the roto- translation constraint between the fluid dynamic surface and the related blade shaft, allows an additional, or alternative, and independent modification of the fluid dynamic pitch to be performed, in relation to the rotation speed of the propeller. According to an advantageous aspect, the propeller according to the present invention, provided with two or more blades, comprises means for synchronizing the rotation motion of the fluid dynamic surface of the blades relative to the respective blade shaft. Since the rotation is rigidly connected to the translation by means of the first inclined section and of the second inclined section of the guide constraint, consequently the synchronization means also make synchronous the translation motion of the fluid dynamic surface relative to the blade shaft.

The synchronism of the translation motion between the various blades can only occur in presence of a rotation of the fluid dynamic surface relative to the blade shaft and therefore only in presence of the first and second section of the guide constraint inclined relative to the axis Y.

Seen that the rotation allowed by the first section is very reduced, to obtain also in this section a synchronism of the translation motion it is necessary that the synchronization means are machined with high accuracy, with high costing results. In certain applications, in the case where said costs are not acceptable from a commercial point of view, however it is possible to obtain satisfactory results by reducing the resulting unbalance of the propeller leaving the first section parallel to the Y axis, but to minimize the length excursion of this section.

According to a possible embodiment, the synchronization means of the translation motion of the fluid dynamic surface of the blades comprise at least one toothed ring which engages with at least one surface integral with the fluid dynamic surface that comprises a plurality of grooves, preferably directed parallel to the axis (Y) of the blade shaft. The toothed ring engages the grooves of the surface integral with the fluid dynamic surface of each blade in such a way that they will result coupled in rotational motion, and therefore in relative translation relative to the respective blade shaft. In doing so, it is possible to avoid that one or more fluid dynamic surfaces of the blades does not commence the roto-translation motion relative to the respective blade shaft upon exceeding a determined value of rotation speed of the propeller, or that the fluid dynamic surfaces of the blades are subjected to roto-translation motion different one from the other.

It should be noted that these synchronization means of the rotation motion of the blades find particular application in the embodiment wherein the first section of the guide constraint allows the roto-translation of the fluid dynamic surface relative to the blade shaft, and vice versa. In fact, in the presence of a component of rotation motion, albeit small, it is possible with the synchronization means, as said with appropriate machining precision, to make synchronous even the translation movement of the blades in the first section of the guide constraint.

BRIEF DESCRIPTION OF THE FIGURES

Further characteristics and advantages of the present invention will be more apparent from the following description, provided by way of example with reference to the accompanying figures, wherein:

• Figure 1 is a perspective view of a possible embodiment of the blade shaft of the propeller according to the present invention;

· Figure 2 shows an enlarged plan view of the guide having a first section parallel to the Y axis of the blade shaft and at least a second section inclined relative to the axis Y of the blade shaft of the propeller according to the present invention;

• Figure 2a shows an enlarged plan view of a further possible embodiment of the guide provided with a first section and a second section inclined relative to the axis Y of the blade shaft of the propeller according to the present invention ;

· Figure 3 is a partial sectional view according to a plane perpendicular to the rotation axis of the cylindrical propeller casing and passing through the rotation axis of the blade shaft, of a first embodiment of the propeller according to the present invention;

• Figure 4 is a partial sectional view of a second possible embodiment of the propeller according to the present invention;

• Figure 5 shows a further possible embodiment of the propeller according to the present invention.

• Figure 6 is a front view partially in section of a propeller blade according to the present invention, provided with means for synchronizing the rotation of the blades; · Figure 6a is a front view partially in section of a propeller blade according to the present invention, provided with two springs for adjusting the motion of the fluid dynamic surface;

• Figure 7 is a schematic view in section along a plane perpendicular to the axis of the blade shaft, of synchronization means of the rotation motion of the blades.

DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE PRESENT INVENTION

Figs. 3-5 show three possible embodiments of the propeller according to the present invention, in partial sectional views according to a plane perpendicular to the rotation axis X of the propeller (illustrated for simplicity only in Fig. 3) and passing through the axis Y of one or more blade shafts 5.

The propeller according to the present invention comprises a hollow external cylindrical casing 2 and an engine shaft operated by an engine, not shown in the figures.

The engine shaft is coupled, directly or indirectly, coaxially to the external cylindrical casing 2, for example by means of a hub, in such a manner as to allow transmission of rotary motion from the engine shaft to the cylindrical casing 2. The propeller also comprises one or more blades 3 (only one blade 3 is shown in Figs. 4 and 5 for simplicity), each of which comprises a fluid dynamic surface 4 adapted to generate the fluid dynamic thrust forces, following the rotation motion of the propeller and the incidence with the fluid in which the propeller is immersed, according to a given fluid dynamic pitch, i.e. in relation to the angle of incidence of the fluid dynamic surface 4 with the fluid that strikes the blade.

Each blade 3 also comprises at least one blade shaft 5 which essentially performs the function of connecting and of constraining the fluid dynamic surface 4 to the cylindrical propeller casing 2.

More in detail, as can be seen in the accompanying figures, each fluid dynamic surface 4 comprises an internal section 4.1 , appropriately shaped to allow insertion therein of at least part of the related blade shaft 5.

In other words, the blades 3 are constrained to the cylindrical propeller casing 2 by means of at least one blade shaft 5 having an axis Y substantially perpendicular relative to the rotation axis X of the propeller, this latter generally coinciding with the rotation axis of the cylindrical casing 2.

The blade shafts 5 can be constrained to the cylindrical propeller casing 2 in such a manner as to be fixed relative thereto, or, according to a possible embodiment which shall be described in more detail hereunder, they can be pivoted to the cylindrical propeller casing 2 in such a manner as to allow rotation thereof about the axis of pivoting, which generally coincides with, or is parallel to, the axis Y of the blade shaft 5 itself.

The propeller according to the present invention is characterized by comprising at least one guide constraint 1 1 , 12 between the fluid dynamic surface 4 and the respective blade shaft, comprising at least one first section 1 1a and at least one second section l ib. The at least one first section 1 1a is shaped to allow the translation or the roto-translation of the fluid dynamic surface 4 relative to the blade shaft 5, and vice versa, and the at least one second section 1 lb is shaped to allow the roto-translation of the fluid dynamic surface 4 relative to the blade shaft 5, and vice versa.

Each fluid dynamic surface 4 is translatable or roto-translatable (depending on the conformation of the first section of the guide constraint) along the respective blade shaft 5 between an initial position and at least one intermediate position and is roto- translatable between said intermediate position and a final position, and vice versa. As will be seen in more detail below, according to a first embodiment of the first section 1 1 a of the guide constraint, the rotation of the fluid dynamic surface 4 is prevented during the translation between the initial position and the at least one intermediate position. While in the second embodiment of the first section 1 la of the guide constraint, it will allow, as will be seen in more detail below, the roto- translation, with very limited rotational component of the fluid dynamic surface, which determines a very limited modification of the fluid dynamic pitch of the blade. Instead, during the roto-translation of the fluid dynamic surface 4 in the second section 1 lb of the guide constraint, simultaneously with the translation motion along the blade shaft 5, and preferably along its Y axis, it rotates from a first fluid dynamic pitch, corresponding to the intermediate position, to a second fluid dynamic pitch corresponding to the final position, and vice versa.

Rotation of the fluid dynamic surface 4 relative to the related blade shaft 5 takes place preferably about the axis Y of the blade shaft 5.

According to a preferred embodiment, the axis Y of the blade shaft 5 extends substantially in a perpendicular manner relative to the rotation axis X of the propeller, which generally coincides with the drive direction of the propeller during forward and reverse motion.

The only translation motion (if allowed by the first section of the guide constraint) and roto-translation of the fluid dynamic surface 4 relative to respective blade shaft 5 are caused by the centrifugal force acting on this blade, which in turn is caused by rotation of the propeller, and in particular by rotation of the cylindrical casing 2 which is imparted by the engine shaft to which it is coupled in rotation.

Due to the centrifugal force acting on the blade, which will obviously vary as a function of the rotation speed of the propeller, the fluid dynamic surface 4 is translatable or roto-translatable (according to the possible conformations of the first section 1 1a) along the blade shaft 5, between an initial position and an intermediate position, and it is also roto-translatable from the intermediate position to the final position in the second section 1 lb, so that simultaneously to the translation, the fluid dynamic surface 4 rotates about the axis of the related blade shaft 5, in such a manner as to shift from a first fluid dynamic pitch toward a second fluid dynamic pitch, and vice versa.

According to a possible embodiment the at least one guide constraint comprises at least one guide surface 1 1 and at least one relevant slider 12 integral respectively with the blade shaft 5 and the fluid dynamic surface 4, or vice versa. The guide surface 1 1 comprises at least one first section 1 1a shaped to allow the translation or the roto-translation of the fluid dynamic surface relative to the blade shaft, and vice versa, and at least one second section 1 lb shaped to allow the roto-translation of the fluid dynamic surface relative to the blade shaft, and vice versa.

According to a possible embodiment the at least one first section 1 la is parallel to the axis (Y) of the blade shaft, and the at least one second section 1 lb is inclined relative to the axis (Y) of the blade shaft.

Figure 1 shows a perspective view of a blade shaft 5 usable in a propeller according to the present invention, provided with a plurality of guides 1 1 , comprising in turn, at least one first section 1 1 a parallel to the Y axis of the blade shaft 5 and at least one second inclined section 1 lb relative to the axis Y of the blade shaft 5.

Figure 2 shows a schematic plan view of the guides 11 of the blade shaft 5 illustrated in Figure 1.

Instead, Figure 2a shows a second possible embodiment in which the first section 1 la and the second section 1 lb are inclined relative to the axis (Y) of the blade shaft 5. Obviously, the guide 1 1 can be produced on the fluid dynamic surface 4 and the related slider 12 on the blade shaft 5, according to alternative embodiments. Moreover, the guide 1 1 and the related slider 12 can be produced directly on surfaces of the fluid dynamic surface 4 and of the blade shaft 4, or on elements or sections integral therewith.

As shown in Figures 1 , 2 and 2a, the first section 1 1 a of the guide 1 1 comprises a first and a second end 13 and 14, and during operation, the slider 12 is in correspondence of the first and second end of the first section 1 l a of the guide 1 1, respectively, when the fluid dynamic surface 4 is respectively in said initial position and in said intermediate position, of its motion along the respective blade shaft 5. The second section 1 lb of the guide 11 comprises a first and a second end 15 and 16, and during operation, the slider 12 is in correspondence with the first and second ends 15 and 16 of second section l ib of the guide 1 1 , respectively, when the fluid dynamic surface 4 is respectively in said intermediate position and in said final position, of its motion of roto-translation along the respective blade shaft 5.

In other words, in the embodiment illustrated in Figures 1 , 2 and 2a, the first section 1 1a and the second section l ib of the guide 1 1 are placed in succession and the second end 14 of the first section 1 1a corresponds to the first end 15 of the second section 1 lb of the guide 1 1.

It should also be noted that in Figure 2 and 2a are illustrated different positions of the slider 12 in the two guides 1 1 in the right part of the figures. In detail, looking at Figures 2 and 2a, the slider 12 is illustrated at a high position during the translation along the first section 1 1a between the ends 13 and 14 (between the initial position and the intermediate position). Immediately below, the slider 12 is shown in an intermediate position, i.e. in correspondence of the end of the first section 1 1a and the beginning of the second section 1 lb.

Still further down, the slider 12 is represented during the sliding in the second section l ib (between the ends 15 and 16, i.e. between the intermediate position and the final position), which causes the roto-translation of the fluid dynamic surface 4.

Preferably, the first section 1 1a of the guide 1 1 precedes the second section l ib thereof along the direction of movement, towards the outside, imposed by centrifugal force.

As shown in Figures 1 and 2, the first section 1 la of the guide 1 1 is arranged parallel to the axis Y of the blade shaft 5, in any case the first section is parallel to the radial direction relative to the propeller rotation axis.

It should be noted that the first section 1 1 a may be replaced with any other constraint means between the fluid dynamic surface 4 and the respective blade shaft 5, adapted to determine only the radial displacement of the fluid dynamic surface 4 relative to the rotation axis X of the propeller, and also such as to prevent rotation about said radial direction of the fluid dynamic surface itself. The second section l ib of the guide 1 1 is inclined relative to a vertical axis, represented by the axis Y' in the plan view in Figure 2, by an angle a2 of approximately 40°. Note that the axis Y' represented in Figure 2 is parallel to the Y axis of the blade shaft 5 and therefore the inclination angles here and hereafter mentioned can be referred to the axis Y of the blade shaft 5. However, it should be noted that according to other possible embodiments said inclination angle a2 of the second section relative to the vertical (i.e. relative to the Y axis) can be suitably modified depending on the constructive requirements, taking into account that said angle determines the rotation of the fluid dynamic surface 4 about the blade shaft as a function of its displacement along the blade shaft 5.

In doing so, as an increase in rotation speed of the propeller occurs, the fluid dynamic surface 4 will be first subjected to a translation motion only (without modification of the fluid dynamic pitch) relative to the blade shaft 5 in the first section 1 1a, and subsequently (exceeded the intermediate position) will be subjected to a roto-translation motion relative to the respective blade shaft 5, in the second section 1 lb, which will result in the modification of the fluid dynamic pitch. As will be clear to a person skilled in the art, the motion of the slider 12 between the ends 13 and 14 of the first section 1 la of the guide does not involve the modification of fluid dynamic pitch since the rotation of the fluid dynamic surface 4 relative to the blade shaft 5 is impeded. In doing so, the fluid dynamic pitch can be maintained at a preset value until it reaches a given value of the rotation speed of the propeller. Instead, the movement between the ends 15 and 16 of second section 1 lb of the guide 1 1 that are achieved by the relative slider 12, determine the attainment by the fluid dynamics surface 4 of the first and second fluid dynamic pitch, as a result of the roto- translation motion about the corresponding blade shaft 5. In other words, a further increase of the rotation speed of the propeller, relative to the one that determines the only translation of the fluid dynamic surface until reaching the second end 14 of the first section (intermediate position) determines the roto-translation movement of the fluid dynamic surface relative to the blade shaft by means of the movement of the slider 12 inside the second section l ib of the guide 1 1 which, as mentioned, also causes the rotation of the fluid dynamic surface 4, and therefore the pitch modification.

In the embodiment represented in Figure 2a, instead, the first section 1 1 a is shaped to allow the roto-translation of the fluid dynamic surface, preferably with a very limited rotation component that determines a very limited modification of the fluid dynamic pitch, which therefore remains substantially unchanged. More in detail, as shown in Figure 2a the first section 1 la of the guide 1 1 is inclined relative to the axis Y of the blade shaft 5 and the second section 1 lb is inclined relative to the axis Y of the blade shaft 5. The inclination al of the first section 1 la relative to the axis Y of the blade shaft 5 is less than the inclination cc2 of the second section 1 lb relative to the axis Y of the blade shaft 5. For simplicity of illustration, as done also in Figure 2, the inclination angles are referred to a vertical axis Y' which is parallel to the Y axis of the blade shaft 5.

In doing so, due to the centrifugal force acting upon the blade, it will be movable between an initial position and an intermediate position, determining the translation, and at the same time a limited rotation, of the fluid dynamic surface 4 relative to the blade shaft 5, by means of the sliding of the slider 12 in the first section 1 la of the guide 1 1 which is parallel to the axis Y. Said motion determines a limited modification of the fluid dynamic pitch until it reaches a certain rotation speed of the propeller (intensity of centrifugal force). As will be clear to a person skilled in the art, the motion of the slider 12 between the ends 13 and 14 of the first section 1 la of the guide will result in a movement of roto-translation, with very limited rotation component since the inclination angle al of the first section 1 1a is very small, preferably equal to a few degrees. It follows that the limited rotation of the fluid dynamic surface 4 will result in a limited modification of the fluid dynamic pitch that will remain substantially unchanged.

In other words, the translation component is the predominant component of rotation in the roto-translation motion in the case in which the first section 1 1 a of the guide 1 1 is inclined relative to the axis Y of the blade shaft 5. In doing so, the fluid dynamic pitch can be substantially maintained at a preset value until reaching a given value of the rotation speed of the propeller and thanks to, albeit small, rotation component, as will be seen better in the following, it will be possible to synchronize the rotation motion of the blades, and therefore also their translation also in the first section 1 1a through appropriate means 51, 52. Instead, similarly to what was said for the embodiment illustrated in Figures 1 and 2, the movement between the ends 15 and 16 of second section l ib of the guide 1 1 illustrated in Figure 2a, which are achieved by the relative slider 12, determine the attainment by the fluid dynamics surface 4 of the first and second fluid dynamic pitch, as a result of the roto- translation motion about the corresponding blade shaft 5.

It should be noted that in general, the angle oil of the first section 1 la must be less than that a2 of the second section 1 1 b, and in particular the first must be very small (very close to the vertical direction of the Y axis) precisely to cause a roto-translation motion with a very limited rotation component. It should also be noted that, according to further possible embodiments, the first and the second sections 1 1 a and l ib may have opposite inclinations relative to the Y axis of the blade shaft 5. For example, the first section 1 la can have positive inclination, while the second section l ib negative inclination relative to the Y axis, and vice versa.

It must be noted that the initial position of the fluid dynamic surface 4 along the blade shaft 5 is a position proximal to the axis X of the propeller, while the final position of the fluid dynamic surface along the blade shaft is a distal position from the axis X of the propeller, so that the centrifugal force acting upon the blade 3 determines automatic shifting from the initial to the intermediate position, as a result of the only motion of the fluid dynamic surface 4 relative to the blade shaft 5, and the further automatic shift from the intermediate position to the final position, following roto-translation motion of the fluid dynamic surface 4 relative to the blade shaft 5. It must also be noted that the number of the guides 11, and of the corresponding sliders 12 adapted to cooperate therewith by sliding, can be varied appropriately.

In the embodiment shown in the figures, several guides 1 1 provided with at least a first section 1 1a and at least a second section l ib are produced on the external surface 5.1 of the blade shaft 5, and the related sliders 12 are produced on the internal surface 4.2 of the fluid dynamic surface 4, on a lower portion thereof.

As already said, the inclined sections relative to the Y axis and made on the outer cylindrical surface of the blade shaft 5 results in helical sections that allow at least partially the roto-translation between the fluid dynamic surface 4 and the respective blade shaft 5.

The propeller according to the present invention also comprises elastic means 20 to adjust the motion of the at least one fluid dynamic surface 4 relative to the blade shaft 5, and vice versa. More in detail, the elastic means 20 allow the translation or the translation with limited rotation (depending on the two possible embodiments of the first section of the guide constraint) of the fluid dynamic surface 4 along the respective blade shaft 5 from the initial position to the intermediate position, only upon exceeding a predefined rotation speed of the cylindrical body 2 of the propeller about the axis X, and/or allow the roto-translation along the second section of the guide constraint of the fluid dynamic surface 4 along the respective blade shaft 5, from the intermediate position to the final position, only upon exceeding a predetermined rotation speed of the cylindrical body 2 of the propeller about the axis X.

The elastic means 20 are interposed between the fluid dynamic surface 4 and the related blade shaft 5, and preferably comprise one or more springs, or in general, elastically deformable elements.

In the embodiment illustrated in Figure 6a, the propeller is provided with two springs 20 and 20' having extension and diameter different one from the other.

According to a possible embodiment, shown in Fig. 3, the elastic means 20 comprising, for example, a metal leaf spring, are housed in at least one seat 22 positioned between the internal surface 4.2 of the fluid dynamic surface 4 and the external surface 5.1 of the related blade shaft 5.

As can be seen in Fig. 3, the elastic means, and in particular the leaf spring 20, is arranged between at least one abutment surface 25, integral with the fluid dynamic surface 4, and at least one abutment surface 26 integral with the blade shaft 5.

According to possible embodiments, the elastic means may, separately or jointly, control the movement of the fluid dynamic surface in the first section 1 1a of the guide constraint and its roto-translation in the second section l ib of the guide constraint, or only one thereof. As the rotation speed of the propeller increases, and therefore ad the centrifugal force acting on the blades increases, the elastic means 20 are compressed by the fluid dynamic surface 4 that tends to translate or roto- translating with a limited rotation component (depending on two possible embodiments of the first section) from the initial position to the intermediate position and/or roto-translate relative to the blade shaft 5 from the intermediate position to the final position, in the second section 1 lb.

According to a further possible embodiment shown in Figs. 4 and 5, the elastic means 20, comprising for example one or more coil springs, are housed at least partially inside the blade shaft 5.

More in detail, as can be seen in Figs. 4 and 5, a coil spring 20 is housed inside a seat 23, substantially cylindrical, obtained inside the blade shaft 5.

Inside the seat 23 there is also arranged a rod 24, constrained to the fluid dynamic surface 4 in such a manner as to be at least partially displaceable and/or at least partially roto-translatable integrally thereto, relative to the blade shaft 5.

The elastic means, and in particular the spring 20, are arranged between at least one abutment surface 25 of the rod 24, and thus an abutment surface integral with the fluid dynamic surface 4, and at least one abutment surface 26 integral with the blade shaft 5, in such a manner as to determine compression of the elastic element following the translation and/or the roto-translation along the blade shaft 5 of the fluid dynamic surface 4, under the action of the centrifugal force generated by rotation of the cylindrical propeller casing.

In general, it must be noted that in the embodiments shown in the accompanying figures and described above, the elastic means 20 reversibly thrust the fluid dynamic surface 4 toward the initial position and/or the intermediate position, and act against shifting thereof toward the final position by means of their compression, following the movement of the fluid dynamic surface 4 about/along the respective blade shaft 5.

In this manner, during operation of the propeller, the fluid dynamic surface 4 of the blade 3 is caused to translate and/or roto-translate radially about/along the axis Y of the blade shaft 5 and this translation and/or roto-translation motion is opposed in a controlled manner by the elastic means 20.

In fact, the elastic means 20 allow the translation of the fluid dynamic surface 4 along the respective blade shaft 5, from the initial position to the intermediate position, only upon exceeding a predetermined rotation speed of the cylindrical propeller casing about the axis of the propeller.

In fact, the fluid dynamic surface 4 can move from the initial position to the intermediate position substantially without modification of the fluid dynamic pitch as a result of only translation motion relative to the blade shaft or of the roto-translation motion with a very limited rotation component (in the two embodiments of the first section), only when it will overcome the resistance exerted by the elastic means 20, i.e. only when the engine shaft, and therefore the cylindrical propeller casing 2 coupled in rotation thereto, has reached an angular speed such as to make the centrifugal force, to which the fluid dynamic surface is subjected, exceed the opposing force exerted by the elastic means 20. Equally, the roto-translation of the fluid dynamic surface 4 from the intermediate position towards the final position as a result of the roto-translation motion about the blade shaft in the second section, and therefore from the first fluid dynamic pitch to the second one, is permitted only for certain values of rotation speed of the motor shaft, and therefore only for certain intensities of centrifugal force acting on the blade.

As already said, the control action performed on the motion in the first section and the second section of the guide constraint by the elastic means 20 may be joint or separate, or can be provided elastic means 20 for controlling the motion only in the first section or only in the second section. As will be clear at this point of the description, when the fluid dynamic surface 4 reaches the final position, and then the second fluid dynamic pitch, any other motion of roto-translation of it relative to the blade shaft 5 is prevented.

Only when the rotation speed of the cylindrical propeller casing 2 decreases, and therefore when the intensity of the centrifugal force acting on the blade decreases, will the elastic means 20 tend to thrust the fluid dynamic surface 4 toward the initial position and/or towards the intermediate position.

It must also be noted that, advantageously, in the embodiments shown in the accompanying figures, the elastic means 20 are housed in seats 22, 23, respectively between the internal surface 4.2 of the fluid dynamic surface 4 and the external surface 5.1 of the blade shaft 5, and/or inside the blade shaft 5, in such a manner that they are not subjected to external agents.

Positioning inside the shaft also makes it possible to prevent the presence of elastic means interposed between the fluid dynamic surface and the blade shaft from causing an increase in the external dimensions of the fluid dynamic surface 4, which would determine a modification of its profile, with a negative influence on the performance and efficiency of the propeller.

Moreover, one or more gaskets can be provided, in the form of rings or the like, to prevent the entry of fluid between the fluid dynamic surface 4 and the blade shaft 5. The propeller according to the present invention also comprises means 31, 32, 33 to stop translation and/or roto-translation of the fluid dynamic surface 4 relative to the related blade shaft 5, which are preferably selected from limit stops, rings 31 , pins 32. The stop means 31 , 32 can be fixed, or can be housed in a movable manner in specific seats 33.

The stop means make it possible to limit translation and/or roto-translation of the fluid dynamic surface 4 about/along the axis Y of the related blade shaft 5, by modifying the reaching of the initial position and/or the intermediate position and/or the final position, consequently determining a modification of the motion in the first section 1 1a until reaching the intermediate position and a modification of the first and second fluid dynamic pitches achieved by the fluid dynamic surface 4 at the intermediate and final position as a result of the movement in the second section 1 lb. In particular, as mentioned above, the fluid dynamic surface reaches the initial and intermediate position, when are achieved the extremes of the first section 1 1 a of the guide 1 1 , and from the intermediate position moves towards the final position roto- translating between the extremes of the second section 1 lb of the guide 1 1.

According to possible embodiments, the stop means act as extremes of the first and second sections 1 la and 1 lb of the guide 1 1 , and thus limiting the movement of the fluid dynamic surface 4 relative to the blade shaft 5.

In the embodiment illustrated in Figure 3 a ring 31, for example an elastic, plastic or metal ring, or a ring of the Seeger type, is installed on the outer surface 5.1 of the blade shaft 5. As a result of the motion in the first and second sections, at least a section of the fluid dynamic surface 4 reaches the contact position with the ring 31 , thus resulting in the achievement of the final position of the fluid dynamic surface 4 in the motion relative to the blade shaft 5. As shown in Figure 3, the abutment 4.3 arranged at the lower section of the fluid dynamic surface 4, and which substantially corresponds to the abutment surface 25 for the elastic means 20, is intended to reach the contact position with the stop ring 31 , as a result of the motion of the fluid dynamic surface relative to the blade shaft 5, in particular carrying out a translation along the blade shaft indicated by the reference Z in Figure 3.

In the embodiment of Fig. 2, in the same manner as described previously with reference to Fig. 3, a ring 31 is integral with the external surface 5.1 of the blade shaft 5, intended to come into contact with at least one abutment 4.3 of the lower portion of the fluid dynamic surface 4.

With reference now to the embodiment of Fig. 5, a pair of pins 32 or a ring, or similar means, are integral with the internal surface 4.2 of the fluid dynamic surface 4, in such a manner as to be able to slide inside a seat 33 arranged on the external surface 5.1 of the blade shaft 5, thereby limiting the motion of the fluid dynamic surface 4 relative to the blade shaft 5.

As said, according to a preferred embodiment, the propeller according to the present invention is provided with two or more blades 3 comprising a fluid dynamic surface 4 bound to respective blade shaft 5. In order to avoid that the propeller blades 3 may be subjected, under certain conditions, at different rotations (and therefore different translations) of its fluid dynamic surface, 4 relative to that of another blade, the propeller can also be provided with means 51 , 52 to synchronize the rotation motion of the fluid dynamic surface of the blades relative to the respective blade shaft.

Figures 6 and 7 show a possible embodiment of the synchronization means 51 , 52 of the rotational motion of the fluid dynamic surface 4 of the propeller blades 3.

It should be noted that for simplicity of illustration, figures 6 and 7 show a single blade 3, however, it is easy to extend what is represented also to the other propeller blades 3, although not visible.

In the embodiment illustrated in Figures 6 and 7, the synchronization means comprise at least one toothed ring 51 which engages with at least one surface 52 integral to the fluid dynamic surface 4 comprising a plurality of grooves 52a. According to a preferred embodiment, the propeller comprises two toothed rings 51 placed stern and forward of the propeller.

It should be noted that the surface 52 can be realized directly on the fluid dynamic surface, or as in the embodiment illustrated in Figures 6 and 7, it can be arranged on a member 53 constrained to the fluid dynamic surface 4.

Preferably the grooves 52a are directed parallel to the axis (Y) of the blade shaft 5. The toothed ring 51 engages the grooves 52a of the surface 52 integral with the fluid dynamic surface 4 of each blade 3. In doing so, all the fluid dynamic surfaces 4 of the propeller blades 3 are coupled into rotation motion, and therefore into translation, relative to the respective blade shaft 5, avoiding that one or more fluid dynamic surfaces of the blades do not start the roto-translation motion relative to the respective blade shaft upon exceeding a determined value of the propeller rotation speed, or that are subject to the roto-translation motion in a different way one from the other, causing unwanted propeller imbalances.

It should be noted that these synchronization means of the blades motion find particular application in the embodiment in which the first section 1 la of the guide constraint allows the roto-translation of the fluid dynamic surface 4 relative to the blade shaft 5, and vice versa. In fact, the roto-translation motion in the first section of the guide constraint determines a component of rotation motion which, although very small (compared to the translation), manages to make synchronous even the translation motion, provided that the synchronization means are machined with high precision. In fact, the roto-translation movement in the first and in the second section is synchronized by means of the rotation of the ring 51 which imposes the rotation of the fluid dynamic surfaces 4 connected thereto. Consequently also the translation motion is synchronized.

Instead, in the case in which the first section of the guide constraint allows only the translation of the fluid dynamic surface relative to the blade shaft, the synchronization of the translation motion will intervene only in the second section of the guide constraint that determines a roto-translation movement because only in said second section is present a component of rotation motion that can be made synchronous between the different blades. More in detail, the teeth 51 a of the ring gear 51 engage with the grooves 52a in such a way as to permit axial translation movement of the fluid dynamic surface and then of the teeth 51a within the grooves 52a of the surface 52. In particular, the translation movement between the initial position and the intermediate position of the fluid dynamic surface, in the first section of the guide constraint, is permitted by the sliding of the grooves 52a of the surface 52, which as said is integral with the fluid dynamic surface 4, relative to teeth 51 aa of the ring 51 that is restrained so as to be rotatable to the propeller casing. In fact, in the first section of the guide constraint not being present a component of rotary motion, the translation motion cannot be made synchronous by the synchronization means described herein.

When the rotation speed of the propeller increases and the fluid dynamic surfaces 4 of the blades roto-translate between the intermediate position and the final position, and vice versa, in the second section of the guide constraint the movement of roto- translation is synchronized by the rotation of the ring 51 which imposes the rotation of the fluid dynamic surfaces 4 connected thereto, consequently determining also a synchronization of the translation motion.

During operation, the first fluid dynamic surface 4 which starts the motion of roto- translation drags, by way of the ring 51 , the other fluid dynamic surfaces 4 of the other blades 3 by transmitting a roto-translation movement by the same amount.

Advantageously, by way of the propeller according to the present invention it is possible to maintain substantially unchanged the fluid dynamic pitch on a predetermined value until reaching a determined value of rotation speed (in the first section of the guide constraint) and subsequently to change automatically (in the second section of the guide constraint), with increasing of the rotation speed of the engine, and then the centrifugal force acting on the blades, the fluid dynamic pitch. Indeed, the fact that the fluid dynamic surface is constrained in a manner translatable or roto-translatable in the first section of the guide constraint and roto-translatable in the second section of the guide constraint, to the respective blade shaft, and that then there is at least a relative movement between the fluid dynamic surface of the propeller and its blade shaft, can constitute a separate adjustment device, which can optionally be used in addition or in alternative to prior art automatic pitch adjustment systems, such as the one described in the patent WO 2008/075187, which provide for rotation of the blade shaft 5 relative to the cylindrical propeller casing 2, about the axis of pivoting of the blade shaft to the cylindrical casing 2.

In fact, according to a possible embodiment of the propeller according to the present invention, the blade shaft or shafts 5 are pivoted to the cylindrical propeller casing 2 and therefore are rotatable relative thereto along its axis Y, which generally coincides, or is parallel, with the axis of pivoting of the blade shaft to the cylindrical propeller casing.

In this case, the propeller usually comprises a kinematic mechanism for transforming the rotary motion of the engine shaft, into the rotary motion of each blade shaft about its axis of pivoting to the cylindrical propeller casing.

More in detail, said kinematic mechanism determines rotation of the blade shafts about their axis of pivoting, thus varying the angle of incidence of the fluid dynamic surface of the blades relative to the fluid (and therefore the fluid dynamic pitch), when the engine shaft rotates in relation to the cylindrical propeller casing by a non zero rotation angle, or vice versa.

The kinematic mechanism for transforming the rotary motion, not completely represented in the accompanying figures, is, for example, of the type comprising a truncated-cone shaped gear pinion 40, integral with the root of each blade shaft 5 (see in particular Fig. 3), i.e. at the end of the blade shaft housed inside the propeller casing.

The engine shaft is provided with a gear wheel integral with a central truncated-cone shaped pinion which permanently meshes the pinions 40 of the blade shafts 5, so that rotation of the central pinion relative to the cylindrical propeller casing 2 causes corresponding rotation of the blade shafts 5 about the respective axes Y of pivoting to the propeller casing, or vice versa.

This rotation of each blade shaft 5, and therefore of the fluid dynamic surface constrained thereto, causes variation of the relative angle of incidence and therefore of the fluid dynamic pitch of the propeller.

The kinematic mechanism described above can naturally be replaced with equivalent means which, by means of relative rotation between the engine shaft and the cylindrical propeller casing, allow variation of the fluid dynamic pitch, transforming the rotation motion of the engine shaft into rotation of the blade shafts about their axis of pivoting, and vice versa.

In the embodiment described above, in which the blade shafts 5 in the propeller are pivoted to the cylindrical casing 2 in such a manner as to be rotatable about their axis Y, and also provided with a kinematic mechanism coupled to the engine shaft, and/or to the cylindrical propeller casing, and to the blade shafts, for adjusting the rotary motion of the blade shaft relative to the cylindrical propeller casing, the constraint of at least partially translation and at least partially roto-translation between the fluid dynamic surface 4 and the related blade shaft 5, according to the present invention, allows an additional, or alternative, and independent variation of the fluid dynamic pitch, in relation to the rotation speed of the propeller and of the centrifugal force acting on the blades.

In other words, the constraint of the fluid dynamic surface 4 of the blade relative to the blade shaft 5 provides an independent adjustment of the fluid dynamic pitch of the blade in addition to that obtainable by means of kinematic mechanisms for pitch adjustment, such as the one described in WO2008/075187, which act by modifying rotation of the blade shaft about the axis of pivoting to the cylindrical propeller casing, as a function of the operating conditions of the propeller, and in particular as a function of the relative rotation of the engine shaft relative to the cylindrical propeller casing, which can also advantageously be controlled by interposing one or more elastic elements, as described in the patent WO2008/075187.

In other words, the guide constraint of the blade allow independent adjustment of the fluid dynamic pitch, and in particular switching from a first fluid dynamic pitch to a second fluid dynamic pitch, in relation to the rotation speed of the propeller.

Optionally, the second pitch reached by means of roto-translation of the fluid dynamic surface 4 relative to the blade shaft 5 corresponds to the base pitch, or initial pitch, of the automatic pitch adjustment interval by means of an adjustment device that acts by controlling rotation of the blade shaft about the axis of pivoting to the cylindrical propeller casing, of the type described in WO2008/075187. In fact, as stated previously, when the fluid dynamic surface 4 reaches the final position of the roto-translation motion relative to the blade shaft, the two elements are integral, and a rotation of the blade shaft relative to its axis of pivoting to the propeller casing would cause integral rotation of the fluid dynamic surface 4 and consequent modification of the fluid dynamic pitch.

Claims

1. A propeller (1) of the type comprising an external cylindrical casing (2) coupled directly or indirectly to an engine shaft in a manner rotatable about the axis (X) of the propeller, and at least one blade (3) provided with at least one fluid dynamic surface (4) constrained to a related blade shaft (5), which is in turn constrained to said external cylindrical casing (2) to be driven in rotation about the axis (X) of the propeller, said blade shaft (5) having its axis (Y) extending in a direction incident to the axis (X) of the propeller and said at least one fluid dynamic surface (4) being driven by said blade shaft in rotation about the axis of the propeller, characterized in that it comprises at least one guide constraint (1 1 , 12) between said at least one fluid dynamic surface (4) and the respective blade shaft (5), said at least one guide constraint comprising at least one first section (1 1a) and at least one second section (1 lb), said at least one first section (1 1a) being shaped to allow the translation or the roto-translation of said fluid dynamic surface (4) relative to said blade shaft (5), and vice versa, said at least one second section (l ib) being shaped to allow the roto- translation of said fluid dynamic surface (4) relative to said blade shaft (5), and vice versa.

2. The propeller according to claim 1, characterized in that said at least one first section (1 la) is shaped to allow the roto-translation of said fluid dynamic surface (4) relative to said blade shaft (5), and vice versa, the rotation allowed by said at least one first section (1 1a) being less than the rotation allowed by said at least one second section (l ib), when the same translation occurs.

3. The propeller according to claim 1 or 2, wherein said at least one guide constraint comprises at least one guide surface (1 1) and at least one relevant slider (12) integral respectively to said blade shaft (5) and said fluid dynamic surface (4), or vice versa, said at least one guide surface (1 1) comprising at least one first section (1 1 a) shaped to allow the translation or the roto-translation of said fluid dynamic surface (4) relative to said blade shaft (5), and vice versa, and at least one second section (l ib) shaped to allow the roto-translation of said fluid dynamic surface (4) relative to said blade shaft (5), and vice versa.

4. The propeller according to claim 3, wherein said at least one first section (1 1a) is parallel to the axis (Y) of said blade shaft (5) and said at least one second section (1 lb) is inclined relative to the axis (Y) of said blade shaft (5).

5. The propeller according to claim 3, wherein said at least one first section (1 la) is inclined relative to the axis (Y) of said blade shaft (5) and said at least second section (1 lb) is inclined relative to the axis (Y) of said blade shaft (5), the inclination (al) of said at least one first section (1 1a) relative to the axis (Y) of said blade shaft (5) being smaller than the inclination (a2) of said at least one second section (l ib) relative to the axis (Y) of said blade shaft (5).

6. The propeller according to any claims 3 to 5, wherein said at least one first section (Ha) comprises at least one first (13) and at least one second (14) end, said slider

(12) reaching said at least one first (13) and at least one second (13) end respectively when said at least one fluid dynamic surface (4) is in the initial position and in an intermediate position.

7. The propeller according to any claims 3 to 6, wherein said at least one second section (l ib) comprises at least one first (15) and at least one second (16) end, said slider (12) reaching said at least one first (15) and at least one second (16) end, respectively, when said at least one fluid dynamic surface (4) is in an intermediate position and in the final position.

8. The propeller according to any preceding claims, characterized in that said at least one first section (1 la) is in position close to the axis (X) of the propeller and said at least one second section (1 lb) is in position distal from the axis (X) of the propeller.

9. The propeller according to any preceding claims, characterized in that it comprises elastic means (20) to adjust the motion of said at least one fluid dynamic surface (4) relative to said blade shaft (5).

10. The propeller according to claim 9, characterized in that said elastic means (20) allow the translation or the roto-translation of said fluid dynamic surface (4) relative to the respective blade shaft (5) in said at least one first section (1 1 a) and/or the roto- translation of said fluid dynamic surface (4) relative to the respective blade shaft (5) in said at least one second section (l ib), only upon exceeding a predetermined rotation speed of the cylindrical propeller casing (2) about the axis of the propeller.

1 1. The propeller according to any one of claims 9 or 10, wherein said elastic means (20) are interposed between said at least one fluid dynamic surface (4) and the related blade shaft (5) and/or are housed at least partially inside said at least one blade shaft (5).

12. The propeller according to any claims 9 to 1 1, wherein said elastic means (20) comprise at least one spring.

13. The propeller according to any one of the preceding claims, characterized in that it comprises means (31, 32, 33) to stop roto-translation of said fluid dynamic surface (4) relative to the related blade shaft (5).

14. The propeller according to claim 13, wherein said stop means are selected from limit stops, or rings (31), or pins (32) movable in specific seats (33).

15. The propeller according to any one of the preceding claims, characterized in that said at least one blade shaft (5) is pivoted to said cylindrical propeller body (2) and is rotatable about its axis (Y).

16. The propeller according to claim 15, characterized in that it comprises at least one kinematic mechanism coupled to said engine shaft, and/or to said cylindrical propeller casing (2), and to said at least one blade shaft (5), for adjusting the rotary motion of said blade shaft (5) relative to said cylindrical propeller casing (2) about said axis (Y) of said blade shaft (5).

17. The propeller according to any preceding claims, characterized in that it comprises two or more blades (3) each with at least one fluid dynamic surface (4) constrained to a respective blade shaft (5) and means (51 , 52) to synchronize the rotation motion of the fluid dynamic surface of said two or more blades (3), relative to the respective blade shaft (5).

18. The propeller according to claim 17, wherein said means (50) for synchronization of the rotation motion of the fluid dynamic surface (4) of said two or more blades (3) comprise at least one toothed ring (51) which engages with at least one surface (52) comprising a plurality of grooves (52a) integral to said fluid dynamic surface (4).

19. The propeller according to claim 18, wherein said grooves (52a) are directed parallel to the axis (Y) of said blade shaft (5).